4.7, MPG, short fuel trim data, O2 Voltage Data - JeepForum.com
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post #1 of 20 Old 04-05-2021, 08:36 PM Thread Starter
Sciencediet66
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4.7, MPG, short fuel trim data, O2 Voltage Data

Hey y’all, still trying to track down the MPG drain on this new to me 2006, 4.7 WK. so far I’m from 8.5 MPG Highway right out of the used lot to about 12.5-13, mostly mixed city Highway. It has had the top end sea foamed and cleaned out, it got quieter after the cleaning, running fresh oil, new Spark Plugs, Champs gaped to .40. New Injectors with 12 ports (The one from MartinBuilt YouTube video). I have been checking the last few components which could be bad on the car which can cause MPG to drop. I just did the suspension, it’s 2 wheel drive with new struts and shocks, running Cooper, mildly aggressive 245,65 R17s. And to my Knowledge it has the factory 3.73. I have it hooked up to Vacuum Inches of Mercury gauge,I have tracked down all the leaks I can Find, it pulls 17-21 inches of Mercury at Idle, and steady 17 in drive, both Measured with AC off since it creates a small amount of vacuum leak. My next idea was Bad 02 sensors so I have gathered some data, I’m not a Mechanic and I’m still learning so I’m hoping someone can tell me what I’m looking at. To me, the two banks do not seem to be behaving the same, again don’t know much, any guidance would be appreciated, this is my daily driver in Miami for work, 25 miles each day at about two gallons is rough.... 5abf9897-cb3c-4ae6-9bc2-4744c4b96c83_1617676607184.jpg

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post #2 of 20 Old 04-05-2021, 10:22 PM
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focusing on B1S1 - Why am seeing several graphs, are you snapping throttle, changing RPM ?

When I see the price of OEM I think aftermarket.
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post #3 of 20 Old 04-05-2021, 10:32 PM
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Short term fuel trim data doesn't tell much without long term fuel trim data. The short term fuel trim is just the instant adjustment to whatever long term fuel trim has been made over time. So, to say it has +10% short term trim means one thing if the long term trim on the same bank is +15% (that bank is really running lean), but it may mean nothing if the long term trim is at or near zero (short term fuel trim up to +/- 10% isn't totally out of the ordinary and probably not significant in the absence of any long term trim). And it may mean something very different if the long term trim is -20% (that bank has been way too rich, and is now too lean, it could mean whatever was causing the rich condition which led to the -20% LTFT has gone away and the PCM is now trimming back towards neutral trim).

O2 sensors are highly unlikely to be responsible for poor fuel economy. Yours all look to me like they are responding appropriately, but it's hard to tell in such short snapshots with varying scales, where it doesn't look like the throttle is constant. It looks like your catalytic converters are in reasonably good shape, I guess.

The '06 2wd 4.7's were only rated for 14 city, 18 hwy, 15 combined. Your mileage isn't far off, especially if it involves stop and go on the highway.

Also, what is the original tire size on the placard attached to your driver's door post? A lot of them came with 235/65R17's, while 245/65R17's were part of several packages. If your Jeep originally came with 235's and hasn't been updated to the current size, your vehicle is slightly underestimating your speed and distance, which would affect the economy it calculates. However, the difference between those two sizes probably wouldn't amount to 1mpg. Speaking of tires, one of the best ways to destroy fuel economy is run underinflated. Have you made sure your tires are fully inflated? I assume you've checked your air filter.


As far as the injectors, no idea why you would change them since you haven't said what was supposedly wrong with them, but if you're going to reference something like a video as a reason for something rather than explain the reason yourself, at least link the video rather than expect someone trying to help you to go track down some random YouTube video and watch it to understand what has been done and why. Just my two cents.


Edit: Ok, I went and watched
. Any mod that requires you grind off most of the lip on the fuel rail that the injector retaining clips engage would be a non-starter for me. If you did that, keep a close eye (and nose) out for fuel leaks. And the fact that he mentioned those were the third or fourth set of injectors he's put on that Jeep is also a little intriguing. He claims his fuel economy shot way up after installing those injectors, but he never explained exactly how replacing injectors would cause a major jump in fuel economy. Unless he had an injector (or several) that were leaking fuel, it just doesn't make any sense. The PCM will adjust the injector pulse of whichever injector it's connected to (as long as the injector coil is compatible with the PCM) to achieve the proper A/F mixture. Unless an injector is incapable of spraying the proper amount of fuel (either can't spray enough, or can't spray little enough within the acceptable pulse width), the same amount of fuel is getting injected per volume of metered air, regardless of the injector. If you put a higher volume injector in, the computer will just shorten the injector pulse until it achieves the A/F mixture it wants. The only time to replace an injector is if it's malfunctioning. And then, replace it with the same. The only time to change to a different injector would be if you're somehow introducing a lot more air into the cylinders (i.e. forced induction) and the existing injectors can't inject enough fuel fast enough.

Last edited by Rick_H; 04-05-2021 at 11:43 PM. Reason: Went and found the video.
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post #4 of 20 Old 04-06-2021, 07:14 AM Thread Starter
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Short term fuel trim data doesn't tell much without long term fuel trim data. The short term fuel trim is just the instant adjustment to whatever long term fuel trim has been made over time. So, to say it has +10% short term trim means one thing if the long term trim on the same bank is +15% (that bank is really running lean), but it may mean nothing if the long term trim is at or near zero (short term fuel trim up to +/- 10% isn't totally out of the ordinary and probably not significant in the absence of any long term trim). And it may mean something very different if the long term trim is -20% (that bank has been way too rich, and is now too lean, it could mean whatever was causing the rich condition which led to the -20% LTFT has gone away and the PCM is now trimming back towards neutral trim).

O2 sensors are highly unlikely to be responsible for poor fuel economy. Yours all look to me like they are responding appropriately, but it's hard to tell in such short snapshots with varying scales, where it doesn't look like the throttle is constant. It looks like your catalytic converters are in reasonably good shape, I guess.

The '06 2wd 4.7's were only rated for 14 city, 18 hwy, 15 combined. Your mileage isn't far off, especially if it involves stop and go on the highway.

Also, what is the original tire size on the placard attached to your driver's door post? A lot of them came with 235/65R17's, while 245/65R17's were part of several packages. If your Jeep originally came with 235's and hasn't been updated to the current size, your vehicle is slightly underestimating your speed and distance, which would affect the economy it calculates. However, the difference between those two sizes probably wouldn't amount to 1mpg. Speaking of tires, one of the best ways to destroy fuel economy is run underinflated. Have you made sure your tires are fully inflated? I assume you've checked your air filter.


As far as the injectors, no idea why you would change them since you haven't said what was supposedly wrong with them, but if you're going to reference something like a video as a reason for something rather than explain the reason yourself, at least link the video rather than expect someone trying to help you to go track down some random YouTube video and watch it to understand what has been done and why. Just my two cents.


Edit: Ok, I went and watched
. Any mod that requires you grind off most of the lip on the fuel rail that the injector retaining clips engage would be a non-starter for me. If you did that, keep a close eye (and nose) out for fuel leaks. And the fact that he mentioned those were the third or fourth set of injectors he's put on that Jeep is also a little intriguing. He claims his fuel economy shot way up after installing those injectors, but he never explained exactly how replacing injectors would cause a major jump in fuel economy. Unless he had an injector (or several) that were leaking fuel, it just doesn't make any sense. The PCM will adjust the injector pulse of whichever injector it's connected to (as long as the injector coil is compatible with the PCM) to achieve the proper A/F mixture. Unless an injector is incapable of spraying the proper amount of fuel (either can't spray enough, or can't spray little enough within the acceptable pulse width), the same amount of fuel is getting injected per volume of metered air, regardless of the injector. If you put a higher volume injector in, the computer will just shorten the injector pulse until it achieves the A/F mixture it wants. The only time to replace an injector is if it's malfunctioning. And then, replace it with the same. The only time to change to a different injector would be if you're somehow introducing a lot more air into the cylinders (i.e. forced induction) and the existing injectors can't inject enough fuel fast enough.
This car has not had any codes, but out of curiosity I wanted to see if the fuel rail had pressure, when I pressed the valve on the rail, there was no pressure. When I removed the file line, all 8 had drips, no code, I looked at them when I got the car because it smelled of a rich condition and I was already doing spark plugs. You are right, I did notice today driving to work my MPG seems to be very close to factory now, as far as long term trip, and the random snap shots, I can’t upload a video directly but I’ll see if I can on another platform and link it, my concern was if the O2 sensors were bad. I don’t know enough but I had seen voltage jumps which in retrospect you can not see on the snapshot. As for cutting metal off, I did not, I simply did not use the clips and they are pressure fit snug, no issues the last 500 miles. I added the snapshot of the comparison of bank 1 and 2 downstream with the vehicle speed and throttle position. From what Iv seen the voltage is flat, but high for bank 1 and then irregular for bank 2. I understand without live data it’s difficult to gauge anything
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post #5 of 20 Old 04-06-2021, 07:15 AM Thread Starter
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post #6 of 20 Old 04-06-2021, 09:54 AM Thread Starter
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Quote:
Originally Posted by Rick_H View Post
Short term fuel trim data doesn't tell much without long term fuel trim data. The short term fuel trim is just the instant adjustment to whatever long term fuel trim has been made over time. So, to say it has +10% short term trim means one thing if the long term trim on the same bank is +15% (that bank is really running lean), but it may mean nothing if the long term trim is at or near zero (short term fuel trim up to +/- 10% isn't totally out of the ordinary and probably not significant in the absence of any long term trim). And it may mean something very different if the long term trim is -20% (that bank has been way too rich, and is now too lean, it could mean whatever was causing the rich condition which led to the -20% LTFT has gone away and the PCM is now trimming back towards neutral trim).

O2 sensors are highly unlikely to be responsible for poor fuel economy. Yours all look to me like they are responding appropriately, but it's hard to tell in such short snapshots with varying scales, where it doesn't look like the throttle is constant. It looks like your catalytic converters are in reasonably good shape, I guess.

The '06 2wd 4.7's were only rated for 14 city, 18 hwy, 15 combined. Your mileage isn't far off, especially if it involves stop and go on the highway.

Also, what is the original tire size on the placard attached to your driver's door post? A lot of them came with 235/65R17's, while 245/65R17's were part of several packages. If your Jeep originally came with 235's and hasn't been updated to the current size, your vehicle is slightly underestimating your speed and distance, which would affect the economy it calculates. However, the difference between those two sizes probably wouldn't amount to 1mpg. Speaking of tires, one of the best ways to destroy fuel economy is run underinflated. Have you made sure your tires are fully inflated? I assume you've checked your air filter.


As far as the injectors, no idea why you would change them since you haven't said what was supposedly wrong with them, but if you're going to reference something like a video as a reason for something rather than explain the reason yourself, at least link the video rather than expect someone trying to help you to go track down some random YouTube video and watch it to understand what has been done and why. Just my two cents.


Edit: Ok, I went and watched
. Any mod that requires you grind off most of the lip on the fuel rail that the injector retaining clips engage would be a non-starter for me. If you did that, keep a close eye (and nose) out for fuel leaks. And the fact that he mentioned those were the third or fourth set of injectors he's put on that Jeep is also a little intriguing. He claims his fuel economy shot way up after installing those injectors, but he never explained exactly how replacing injectors would cause a major jump in fuel economy. Unless he had an injector (or several) that were leaking fuel, it just doesn't make any sense. The PCM will adjust the injector pulse of whichever injector it's connected to (as long as the injector coil is compatible with the PCM) to achieve the proper A/F mixture. Unless an injector is incapable of spraying the proper amount of fuel (either can't spray enough, or can't spray little enough within the acceptable pulse width), the same amount of fuel is getting injected per volume of metered air, regardless of the injector. If you put a higher volume injector in, the computer will just shorten the injector pulse until it achieves the A/F mixture it wants. The only time to replace an injector is if it's malfunctioning. And then, replace it with the same. The only time to change to a different injector would be if you're somehow introducing a lot more air into the cylinders (i.e. forced induction) and the existing injectors can't inject enough fuel fast enough.
This car has not had any codes, but out of curiosity I wanted to see if the fuel rail had pressure, when I pressed the valve on the rail, there was no pressure. When I removed the file line, all 8 had drips, no code, I looked at them when I got the car because it smelled of a rich condition and I was already doing spark plugs. You are right, I did notice today driving to work my MPG seems to be very close to factory now, as far as long term trip, and the random snap shots, I can’t upload a video directly but I’ll see if I can on another platform and link it, my concern was if the O2 sensors were bad. I don’t know enough but I had seen voltage jumps which in retrospect you can not see on the snapshot. As for cutting metal off, I did not, I simply did not use the clips and they are pressure fit snug, no issues the last 500 miles. I added the snapshot of the comparison of bank 1 and 2 downstream with the vehicle speed and throttle position. From what Iv seen the voltage is flat, but high for bank 1 and then irregular for bank 2. I understand without live data it’s difficult to gauge anything

Your reasoning makes a lot of sense as to why introducing the new injectors is not logical, I admit I had seen a comparison where the original four port “spray” more in a liquid sense and the ones he used “atomize” and have a larger distribution. Weather I bet on the wrong horse or injector is not so much my concern, the MPG did shoot up to almost stock after the plugs and injectors were replaced, the plugs were original from 2006 with .40 clearance, the gap was correct so I took a logical leap and changed the injectors as well. Like I said I’m not a mechanic I’m just trying to make it run as best as I can with my limited but growing understanding.
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post #7 of 20 Old 04-06-2021, 10:49 AM
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post the ECT, and LONG as well as short fuel trims.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 20 Old 04-06-2021, 11:56 AM
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Originally Posted by Sciencediet66 View Post
This car has not had any codes, but out of curiosity I wanted to see if the fuel rail had pressure, when I pressed the valve on the rail, there was no pressure. When I removed the file line, all 8 had drips, no code, I looked at them when I got the car because it smelled of a rich condition and I was already doing spark plugs. You are right, I did notice today driving to work my MPG seems to be very close to factory now, as far as long term trip, and the random snap shots, I canít upload a video directly but Iíll see if I can on another platform and link it, my concern was if the O2 sensors were bad. I donít know enough but I had seen voltage jumps which in retrospect you can not see on the snapshot. As for cutting metal off, I did not, I simply did not use the clips and they are pressure fit snug, no issues the last 500 miles. I added the snapshot of the comparison of bank 1 and 2 downstream with the vehicle speed and throttle position. From what Iv seen the voltage is flat, but high for bank 1 and then irregular for bank 2. I understand without live data itís difficult to gauge anything
If Iím understanding the part Iíve bolded in the quote above, are you saying you did not reinstall the injector retaining clips to the fuel rail before reinstalling it? If thatís the case, the only thing holding those injectors in your fuel rail against the constant 58 p.s.i. fuel pressure (and the higher pressure intermittent pulses) in the rail is the friction fit between the o-ring and rail port, and the two fuel rail hold-down bolts on each side clamping down on them. This is a really, really, bad idea. If one of those injectors does manage to be pushed out of its bore, even if not all the way but just enough to leak, a huge volume of raw fuel may be sprayed all over your hot engine. And it will keep spraying at high volume (thatís what your fuel pump was designed for) until you shut off the ignition. This is a perfect recipe for a catastrophic engine fire.

I thought the modification the guy did in the video was a bad idea because he removed so much of the lip on the rail ports the the retaining clip holds onto so he could rotate the injectors in their bores. But what youíve done makes that seem safe by comparison, at least he put the clips back on the diminished lip. I cannot stress enough how strongly I encourage you to get those retaining clips installed. Even if it requires reinstalling the factory injectors or getting new ones, get the retaining clips on those injectors!

As far as your last data graph, itís unusual to ever see a flat line on an O2 sensor output, and that wasnít the case in your previous graphs. It should also throw a code. The most useful chart would be one with only Bank 1, sensors 1 & 2 (preferably on the same voltage scale, but that may be automatically selected by your app and beyond your control) and another with only Bank 2, sensors 1 & 2, and both on a longer time scale. Iím not familiar with the app youíre using, but on the one I use, if I rotate my phone to landscape it will give me a wider graph and basically keeps compressing the time scale to keep the entire recorded stream on one page, and therefore show a longer time period with lower time resolution. Will yours do the same? That way you could capture a graph over say, 30 seconds, to see how sensor 1 is switching and how sensor 2 shows the converterís effectiveness. You shouldnít be seeing flatlines with the engine running.
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post #9 of 20 Old 04-06-2021, 12:36 PM Thread Starter
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Quote:
Originally Posted by Sciencediet66 View Post
This car has not had any codes, but out of curiosity I wanted to see if the fuel rail had pressure, when I pressed the valve on the rail, there was no pressure. When I removed the file line, all 8 had drips, no code, I looked at them when I got the car because it smelled of a rich condition and I was already doing spark plugs. You are right, I did notice today driving to work my MPG seems to be very close to factory now, as far as long term trip, and the random snap shots, I can’t upload a video directly but I’ll see if I can on another platform and link it, my concern was if the O2 sensors were bad. I don’t know enough but I had seen voltage jumps which in retrospect you can not see on the snapshot. As for cutting metal off, I did not, I simply did not use the clips and they are pressure fit snug, no issues the last 500 miles. I added the snapshot of the comparison of bank 1 and 2 downstream with the vehicle speed and throttle position. From what Iv seen the voltage is flat, but high for bank 1 and then irregular for bank 2. I understand without live data it’s difficult to gauge anything
If I’m understanding the part I’ve bolded in the quote above, are you saying you did not reinstall the injector retaining clips to the fuel rail before reinstalling it? If that’s the case, the only thing holding those injectors in your fuel rail against the constant 58 p.s.i. fuel pressure (and the higher pressure intermittent pulses) in the rail is the friction fit between the o-ring and rail port, and the two fuel rail hold-down bolts on each side clamping down on them. This is a really, really, bad idea. If one of those injectors does manage to be pushed out of its bore, even if not all the way but just enough to leak, a huge volume of raw fuel may be sprayed all over your hot engine. And it will keep spraying at high volume (that’s what your fuel pump was designed for) until you shut off the ignition. This is a perfect recipe for a catastrophic engine fire.

I thought the modification the guy did in the video was a bad idea because he removed so much of the lip on the rail ports the the retaining clip holds onto so he could rotate the injectors in their bores. But what you’ve done makes that seem safe by comparison, at least he put the clips back on the diminished lip. I cannot stress enough how strongly I encourage you to get those retaining clips installed. Even if it requires reinstalling the factory injectors or getting new ones, get the retaining clips on those injectors!

As far as your last data graph, it’s unusual to ever see a flat line on an O2 sensor output, and that wasn’t the case in your previous graphs. It should also throw a code. The most useful chart would be one with only Bank 1, sensors 1 & 2 (preferably on the same voltage scale, but that may be automatically selected by your app and beyond your control) and another with only Bank 2, sensors 1 & 2, and both on a longer time scale. I’m not familiar with the app you’re using, but on the one I use, if I rotate my phone to landscape it will give me a wider graph and basically keeps compressing the time scale to keep the entire recorded stream on one page, and therefore show a longer time period with lower time resolution. Will yours do the same? That way you could capture a graph over say, 30 seconds, to see how sensor 1 is switching and how sensor 2 shows the converter’s effectiveness. You shouldn’t be seeing flatlines with the engine running.
I had not realized that much pressure was directly against the ports, absolutely I’ll be buying the originals if I can’t find clips that do fit.

I’ll try and make those graphs today. Yes that green line is static and high, I have read the voltage for the Dow streams should be around 4.5 and move slowly up and down. Not rapidly like the other downstream in red. Thank you again for the help and safety warning.
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post #10 of 20 Old 04-06-2021, 02:34 PM Thread Starter
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I was able to gather data one Bank 1 and 2 the first image is down streams comparing both banks with long term fuel and the second is up streams compared and long term fuel trim
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post #11 of 20 Old 04-06-2021, 06:28 PM
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I believe either your pictures got posted in the opposite order, or you've mixed up your descriptions. The graph showing the O2 sensors switching high to low and back would be your upstream (sensor 1) sensors, this is your PCM switching your A/F mixture from slightly rich to slightly lean to supply the catalytic converters with unburned oxygen they need to do their job. The downstream O2s (sensor 2) should show a fairly stable O2 level at steady throttle, assuming the converters are working properly.


Also, the ECT @jtec has been asking for is your engine coolant temp. It's important to know, the PCM won't start adjusting fuel ratios based on the O2 data until the vehicle has warmed up and reached a certain temperature and gone into "closed loop". You don't necessarily have to graph it, but at least make a note of what it is when you begin recording data. Presumably, it won't change much during the recording.


Your long term fuel trim is all over the place, and changing much more more frequently and radically than I think it should. It would be better to have graphs with Bank 1 short term and Bank 1 long term fuel trim on one graph, and Bank 2 short term and Bank 2 long term fuel trim on another graph.


Long and short term fuel trims are additive. In other words, your PCM has a program that says "at such and such atmospheric pressure, temperature, and intake air volume, etc. I should fire the injector on each cylinder for X milliseconds to inject exactly the right amount of fuel to mix with the volume of air entering that cylinder, to achieve complete combustion." So, when you first start your vehicle and until your O2 sensors and engine have warmed up enough, your PCM uses that base program to calculate its fuel injector pulse. Once the vehicle goes into "closed loop", it begins monitoring how much unburned oxygen is going out the tailpipe via the O2 sensors. Too much indicates the mixture is too lean, too little means it's too rich. It then uses a variable called "short term fuel trim" to adjust that mixture. If it reads that there is too much oxygen, it needs to increase the amount of fuel it's injecting. So, it pulses the injector for just slightly longer. This is positive short term fuel trim. It's adding fuel to the mixture above what it's baseline program says should be needed given conditions. If it detects the mixture is too rich, it does the opposite and subtracts fuel from the mixture. This is negative short term fuel trim. Short term fuel trim is meant to enable the PCM to respond correctly to temporary conditions which may affect combustion efficiency.


If the PCM sees after a while that this new short term fuel trim seems to be necessary to maintain proper combustion, it will slowly shift it over to what is called the Long Term fuel trim. This gets written as kind of an addendum to the factory programming, and will be remembered and included on every drive cycle. The long term fuel trim (positive or negative) will automatically be added to (or subtracted from) the baseline program fuel program until the PCM sees that it needs to be changed. It becomes essentially the defacto "baseline" fuel program, although if you reset the fuel trims, it would go away and the PCM would return to it's factory baseline program.


From the new "baseline" (long term trim) program, which is the factory fuel program + (or -) the long term fuel trim, the PCM continues to monitor the combustion efficiency via the O2 sensors. Suppose that your vehicle has settled in to a long term fuel trim of +8%. It will automatically fire the injectors long enough to inject its factory baseline fuel amount + 8% forever, unless it sees that this is no longer resulting in the desired combustion efficiency. If it suddenly sees that there is once again not enough oxygen in the exhaust, indicating a lean condition, it will attempt to adapt to the current conditions. But, since it doesn't know if these new conditions are just temporary or the new normal, it doesn't just immediately change the long term fuel trim. It uses the short term fuel trim, and adjusts it to add more fuel. Say, for example, it adds +5% short term fuel to achieve the results it wants. So, what is the total fuel trim now? Well, it's the factory baseline program, plus +8% in the long term trim, plus the +5% short term fuel trim. So, it's now adding +13% over the factory program. If it needs to add this additional 5% short term trim long enough, it slowly begins shifting this additional short term trim over to the long term fuel trim, which will eventually reach that 13%, until the vehicle is running at the desired combustion ratio with little to no short term fuel trim (it's all in long term).


Ideally, a vehicle shouldn't have much long term fuel trim (positive or negative). If it does, it can indicate somethings amiss. For example, a lot of positive long term trim would indicate the PCM is compensating for an ongoing lean condition, which is often a vacuum or intake leak. A vehicle will often have some small and varying amount of short term trim (up to about 10% +/-) and that usually isn't worth chasing, it's just the PCM doing what it's supposed to, and adapting to the instantaneous conditions. It's ordinary.


Your vehicle seems to be showing quite a bit of long term negative fuel trim, which indicates it taking fuel away from the mixture. Quite a bit of fuel at times. Depending on what the short term trim is doing at the same time, massive amounts. The first thing that springs to my mind is if those injectors are dumping considerably more fuel per millisecond of injector pulse, and the PCM is still trying to figure out how much pulse it needs to trim to achieve the proper A/F ratio. Or if possibly one or more of them is sticking open intermittently? I'd think you would have a miss if that were the case. But what I don't understand is why it's bouncing around so much. Long term trim doesn't usually bounce around like that, that is the short term trim's job. That's why it would be nice to have the short term trim overlayed on the long term trim for each bank. The short term trim should always lead the long term trim. Judging by how crazy your long term trim looks, I'd really like to see the short term trim. The PCM must be having an absolute freak out with it. The fact that both banks are kind of crazy makes me doubt it's down to a defective O2 sensor.






Edit to add: Keep in mind, the factory baseline fuel program is based on exactly the injectors specified by the engineers that designed the system. Any other injector which doesn't behave in exactly the same manner is going to require the PCM to make adjustments to its baseline program via fuel trims, just to try to achieve what it would be getting at 0% fuel trim with the factory injectors. I wish the guy that made that video had shown his fuel trims after that swap, before suggesting to people they just randomly yank out their factory injectors and swap them with a totally different spec. But after watching him grind the retaining tabs on the fuel rail down, I suspect he has no idea what fuel trims are, or that he's ever even checked them. That's probably why he said he thought those Bosch injectors he randomly stuck in there first were "screwing with his computer". It probably couldn't compensate for the difference in flow rate between them and the OEM injectors.

Last edited by Rick_H; 04-06-2021 at 06:39 PM.
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post #12 of 20 Old 04-06-2021, 09:49 PM Thread Starter
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Originally Posted by Rick_H View Post
I believe either your pictures got posted in the opposite order, or you've mixed up your descriptions. The graph showing the O2 sensors switching high to low and back would be your upstream (sensor 1) sensors, this is your PCM switching your A/F mixture from slightly rich to slightly lean to supply the catalytic converters with unburned oxygen they need to do their job. The downstream O2s (sensor 2) should show a fairly stable O2 level at steady throttle, assuming the converters are working properly.


Also, the ECT @jtec has been asking for is your engine coolant temp. It's important to know, the PCM won't start adjusting fuel ratios based on the O2 data until the vehicle has warmed up and reached a certain temperature and gone into "closed loop". You don't necessarily have to graph it, but at least make a note of what it is when you begin recording data. Presumably, it won't change much during the recording.


Your long term fuel trim is all over the place, and changing much more more frequently and radically than I think it should. It would be better to have graphs with Bank 1 short term and Bank 1 long term fuel trim on one graph, and Bank 2 short term and Bank 2 long term fuel trim on another graph.


Long and short term fuel trims are additive. In other words, your PCM has a program that says "at such and such atmospheric pressure, temperature, and intake air volume, etc. I should fire the injector on each cylinder for X milliseconds to inject exactly the right amount of fuel to mix with the volume of air entering that cylinder, to achieve complete combustion." So, when you first start your vehicle and until your O2 sensors and engine have warmed up enough, your PCM uses that base program to calculate its fuel injector pulse. Once the vehicle goes into "closed loop", it begins monitoring how much unburned oxygen is going out the tailpipe via the O2 sensors. Too much indicates the mixture is too lean, too little means it's too rich. It then uses a variable called "short term fuel trim" to adjust that mixture. If it reads that there is too much oxygen, it needs to increase the amount of fuel it's injecting. So, it pulses the injector for just slightly longer. This is positive short term fuel trim. It's adding fuel to the mixture above what it's baseline program says should be needed given conditions. If it detects the mixture is too rich, it does the opposite and subtracts fuel from the mixture. This is negative short term fuel trim. Short term fuel trim is meant to enable the PCM to respond correctly to temporary conditions which may affect combustion efficiency.


If the PCM sees after a while that this new short term fuel trim seems to be necessary to maintain proper combustion, it will slowly shift it over to what is called the Long Term fuel trim. This gets written as kind of an addendum to the factory programming, and will be remembered and included on every drive cycle. The long term fuel trim (positive or negative) will automatically be added to (or subtracted from) the baseline program fuel program until the PCM sees that it needs to be changed. It becomes essentially the defacto "baseline" fuel program, although if you reset the fuel trims, it would go away and the PCM would return to it's factory baseline program.


From the new "baseline" (long term trim) program, which is the factory fuel program + (or -) the long term fuel trim, the PCM continues to monitor the combustion efficiency via the O2 sensors. Suppose that your vehicle has settled in to a long term fuel trim of +8%. It will automatically fire the injectors long enough to inject its factory baseline fuel amount + 8% forever, unless it sees that this is no longer resulting in the desired combustion efficiency. If it suddenly sees that there is once again not enough oxygen in the exhaust, indicating a lean condition, it will attempt to adapt to the current conditions. But, since it doesn't know if these new conditions are just temporary or the new normal, it doesn't just immediately change the long term fuel trim. It uses the short term fuel trim, and adjusts it to add more fuel. Say, for example, it adds +5% short term fuel to achieve the results it wants. So, what is the total fuel trim now? Well, it's the factory baseline program, plus +8% in the long term trim, plus the +5% short term fuel trim. So, it's now adding +13% over the factory program. If it needs to add this additional 5% short term trim long enough, it slowly begins shifting this additional short term trim over to the long term fuel trim, which will eventually reach that 13%, until the vehicle is running at the desired combustion ratio with little to no short term fuel trim (it's all in long term).


Ideally, a vehicle shouldn't have much long term fuel trim (positive or negative). If it does, it can indicate somethings amiss. For example, a lot of positive long term trim would indicate the PCM is compensating for an ongoing lean condition, which is often a vacuum or intake leak. A vehicle will often have some small and varying amount of short term trim (up to about 10% +/-) and that usually isn't worth chasing, it's just the PCM doing what it's supposed to, and adapting to the instantaneous conditions. It's ordinary.


Your vehicle seems to be showing quite a bit of long term negative fuel trim, which indicates it taking fuel away from the mixture. Quite a bit of fuel at times. Depending on what the short term trim is doing at the same time, massive amounts. The first thing that springs to my mind is if those injectors are dumping considerably more fuel per millisecond of injector pulse, and the PCM is still trying to figure out how much pulse it needs to trim to achieve the proper A/F ratio. Or if possibly one or more of them is sticking open intermittently? I'd think you would have a miss if that were the case. But what I don't understand is why it's bouncing around so much. Long term trim doesn't usually bounce around like that, that is the short term trim's job. That's why it would be nice to have the short term trim overlayed on the long term trim for each bank. The short term trim should always lead the long term trim. Judging by how crazy your long term trim looks, I'd really like to see the short term trim. The PCM must be having an absolute freak out with it. The fact that both banks are kind of crazy makes me doubt it's down to a defective O2 sensor.






Edit to add: Keep in mind, the factory baseline fuel program is based on exactly the injectors specified by the engineers that designed the system. Any other injector which doesn't behave in exactly the same manner is going to require the PCM to make adjustments to its baseline program via fuel trims, just to try to achieve what it would be getting at 0% fuel trim with the factory injectors. I wish the guy that made that video had shown his fuel trims after that swap, before suggesting to people they just randomly yank out their factory injectors and swap them with a totally different spec. But after watching him grind the retaining tabs on the fuel rail down, I suspect he has no idea what fuel trims are, or that he's ever even checked them. That's probably why he said he thought those Bosch injectors he randomly stuck in there first were "screwing with his computer". It probably couldn't compensate for the difference in flow rate between them and the OEM injectors.
Tomorrow morning I’ll compare the Trims per bank as you asked. I did put the. Jeep into Quick learn mode after the process, what your saying makes a lot of sense and is exactly what he described, a higher volume of fuel which now it would make sense why so much is being cut back and leaned out from the mixture (after your explanation. The cats work, I have 780F degrees or so at Idle and 1350F when moving around town. No knock, no Codes, that 4.7 has been running really well with those injectors which is why I did not at first look for any data on fuel trim. I actually noticed more power in the car and thought I may have a rich condition and it was why I had a lower combined MPG.

Edit: the temp Holds 199.4 most of the day. Running Highway 204 max on idle for long periods no airflow I have seen 207. I made sure to tune in the temps, I know this motor is know for dropping seats and lifter issues
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post #13 of 20 Old 04-07-2021, 02:09 PM Thread Starter
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This chart is short and long trim for bank 1 and under the same set up for bank 2. I can only run 4 graphs so vehicle speed and throttle have not been added. This was between 10-60 miles at times. There was really not much time for any time of consistent speed driving, Miami Highways are just stop and go streets with bigger speed limits...
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post #14 of 20 Old 04-07-2021, 02:33 PM Thread Starter
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Bank 1 short and long with speed and throttle
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post #15 of 20 Old 04-07-2021, 09:06 PM
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The good news is, since your short term trims are fairly neutral, going both above and below zero, your PCM has apparently been able to lean out your A/F ratio enough to get the proper mixture. It's pulled a lot of fuel out in the long term trim to do it. If both your long term and short term trim was staying very negative all the time, it would make me think that those injectors are spraying so much fuel that the PCM cannot compensate enough, and you'd be running rich all the time. That would definitely hurt your fuel economy, and probably eventually burn up your cats. But that isn't the case in these graphs, your short term trim is often adding fuel to offset some of the negative long term trim. But then I look back at the graphs you posted a couple of days ago, and both trims are consistently negative. I just don't get your fuel trims at all.

I'm still puzzled by how much your long term fuel trim jumps around. It's based on a lot of different inputs, so the fact that these graphs reflect a lot of varying throttle positions, speeds, engine loads, is going to contribute a lot of fluctuation. But yours seems kind of wild to me. One thing is for sure, it's always between about -5% and -25%, so it's seeing a considerably more fuel being burned than it expects to, which to me points directly back to those injectors.

It would be nice to see O2 graphs set up just like you had those fuel trim graphs set up. Bank 1, sensors 1 & 2 on one graph and Bank 2 sensors 1 & 2 on another to compare both banks simultaneously and to see if both upstreams are switching and both downstreams are stable. Then if you could do each bank over a graph with RPM and throttle position. Of course, the vehicle needs to be fully warmed up first. For these graphs, it would actually be good if there were a couple of short, wide throttle accelerations included along with some steady throttle.

I don't think the replacement injectors are necessarily hurting anything, including your mileage, because the PCM seems to have been able to reduce fuel delivery via fuel trim enough to find the right A/F mixture (even though it looks pretty chaotic). But I also absolutely don't think they're improving anything, including your mileage. I doubt there's anything wrong with your O2 sensors, but a clearer graph of them would be nice to see. Those you've posted generally look OK to me.

If it were my Jeep, given those fuel trims after 500 miles of driving on the replacement injectors, I would likely put the OEM injectors (or exact equivalents) back in it and get the retaining clips back on them. Especially since it seems like the PCM is having to use up a lot of its fuel trimming ability just to find equilibrium (it can only go up to +/- 30%). On the other hand, I don't think those injectors are going to blow your Jeep up, so if you don't want to yank them, so be it. I still shudder at the thought of no retaining clips on them, though. It would also be interesting to see how many of them stay in the head rather than come out with the rail, if you pull it again.

You mentioned you thought some of the original injectors were leaking, and that would definitely be worth checking before buttoning everything back up. If you had an injector(s) leaking, it would definitely hurt your fuel economy and possibly cause other damage, if it continued to leak when the vehicle was off. I think you said the reason you suspected it was that you pressed the valve on the fuel line and there was no pressure. There are other things than leaky injectors that could cause that, like a bad check valve at the pump allowing fuel to drain out of the line back into the tank when the vehicle is shut off. That can cause long cranking startups, but shouldn't hurt your fuel economy. Putting a fuel pressure gauge on the line and watching it after shutting the vehicle off to see if it holds pressure would be one way to see if you're bleeding off pressure. They can be had pretty cheaply.

Overall, I think your fuel economy isn't far out of whack, considering it sounds like you're doing mostly stop and go driving on the highway in a two ton V8 SUV. My 5.7 will average around 16mpg in mixed city driving and maybe 20 on the highway (MDS), but it only gets about 5-6mpg while accelerating moderately from a stop up to highway speed. You're doing that over and over and over again all the way to work and back. That absolutely murders your average fuel economy. I doubt it would have been much better when the truck was brand new, and I bet you'd see much better economy if you were to go on an extended non-stop highway drive. Heck, just reset your avg fuel economy while holding a steady highway speed and see what kind of immediate reading you get, I imagine it'll be in the upper teens.
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