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post #1 of 11 Old 05-15-2019, 02:09 PM Thread Starter
FergiesJeep
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LS Swap question

So i did a 5.3 vortec swap last summer and was getting 23mpg for the first 3 months now it has dropped off to 14mpg and has lost some of its power any one else have similar problems or thoughts on what is going on. It has a 5.3 vortec 4l60e and np246.

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post #2 of 11 Old 05-16-2019, 04:59 AM
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Originally Posted by FergiesJeep View Post
So i did a 5.3 vortec swap last summer and was getting 23mpg for the first 3 months now it has dropped off to 14mpg and has lost some of its power any one else have similar problems or thoughts on what is going on. It has a 5.3 vortec 4l60e and np246.
MIL light on? Do you have a scanner? Thats going to be the best way to see what your engine is doing. You can get a bluetooth OBD2 scanner for cheap and get the torque app or some other scanner app on your phone. I would start trouble shooting there.

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post #3 of 11 Old 05-16-2019, 05:14 AM
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Originally Posted by FergiesJeep View Post
So i did a 5.3 vortec swap last summer and was getting 23mpg for the first 3 months now it has dropped off to 14mpg and has lost some of its power any one else have similar problems or thoughts on what is going on. It has a 5.3 vortec 4l60e and np246.
MIL light on? Do you have a scanner? Thats going to be the best way to see what your engine is doing. You can get a bluetooth OBD2 scanner for cheap and get the torque app or some other scanner app on your phone. I would start trouble shooting there.

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post #4 of 11 Old 05-16-2019, 08:56 AM
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If you figure this out, please let me know. Mine has never even gotten 14mpg and I can't find anything wrong with a scantool or OBD bluetooth scanner. 12-13mpg is about what I get on average and I'm not aggressive on the throttle. I was trying to diagnose this for a while but after several "fixes" I've kinda given up and surrendered to the thought of "I just have to pay to play". I've changed O2 sensors, MAF sensor, and put the air intake right behind headlight to get the coolest air temps possible.

I have thought about going to a dyno but it just seems silly to me to dyno tune a stock engine on a stock ECU in hopes of getting a few extra mpg. I figured that even if I managed to gain 50% more mpg, it would take me 2-3 years to recoop the dyno cost in fuel at the rate I drive my jeep.


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post #5 of 11 Old 05-17-2019, 10:47 AM Thread Starter
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I have used my scan tool it never shows any problems. i put a diablo tuner on it didnt notice much of a difference. i have tried a a few things almost wondering if my Torque convert is not working properly, i did notice going in and out of 4L weather park or neutral it grinds like the trani is still in gear.
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post #6 of 11 Old 05-17-2019, 12:08 PM
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Originally Posted by FergiesJeep View Post
I have used my scan tool it never shows any problems. i put a diablo tuner on it didnt notice much of a difference. i have tried a a few things almost wondering if my Torque convert is not working properly, i did notice going in and out of 4L weather park or neutral it grinds like the trani is still in gear.
The transfer case doesn't have synchros so that's not that uncommon. As for gearing... Look at http://www.grimmjeeper.com/gears.html and figure out what your rpms should be at your given tire size and gear ratio. Don't be lazy... go measure your rear tires from the ground to the center of your axle. My 35" tires measure 17.75" from ground to axle center so when they're loaded, they are rotating as if it's a 33.5" tire. For the sake of diagnosis, you need that kind of accuracy. The difference between your 4L60E in a locked converter and unlocked converter is about 100-150rpms depending on speed and gear.

I just made this form so you can see and you really need a nice straight section of road and a bluetooth OBD readout or maybe your scan tool can give you that info so you can get a nice clean digital signal. This is the 4L60E and the charts on the left are a fully locked torque converter and the one on the left is a non-functioning or non-locked torque coverter. You may be able to use your scan tool to get information on the torque converter lock up signal as well but it depends on the capability. My scan tool doesn't directly tell me that the torque converter is locked but it will tell me the relative rpm difference between the input shaft and output shaft. If those two numbers are more than 0-2 rpms, I know my torque converter isn't locked.


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post #7 of 11 Old 05-17-2019, 03:22 PM
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Quote:
Originally Posted by Waternut View Post
If you figure this out, please let me know. Mine has never even gotten 14mpg and I can't find anything wrong with a scantool or OBD bluetooth scanner. 12-13mpg is about what I get on average and I'm not aggressive on the throttle. I was trying to diagnose this for a while but after several "fixes" I've kinda given up and surrendered to the thought of "I just have to pay to play". I've changed O2 sensors, MAF sensor, and put the air intake right behind headlight to get the coolest air temps possible.

I have thought about going to a dyno but it just seems silly to me to dyno tune a stock engine on a stock ECU in hopes of getting a few extra mpg. I figured that even if I managed to gain 50% more mpg, it would take me 2-3 years to recoop the dyno cost in fuel at the rate I drive my jeep.

Dyno isn't cheap, $500 but my fuel / air was way off, (stock tune) and since having it done, jeep runs alot better and now watching the MPGs . was able to fine tune the trans shifting too... was worth it...

23mpgs? i'm skeptical...
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post #8 of 11 Old Yesterday, 07:41 AM Thread Starter
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according to the rpm site my tack is way off so either engine is running to fast or stock tach signal is different, I am guessing it is the latter.
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post #9 of 11 Old Yesterday, 02:44 PM
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according to the rpm site my tack is way off so either engine is running to fast or stock tach signal is different, I am guessing it is the latter.
LS engines run off a typical 4 cylinder tach signal. 2 pulses per revolution.


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post #10 of 11 Old Yesterday, 08:02 PM
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23mpgs? i'm skeptical...
MPG is tightly related to BTUs and “watts” of power required to move “x” mass at Y velocity. So often I see high mileage claims after this or that “upgrade” but when the reality is, say, a 10% change in /efficiency/ between motor ‘a’ and motor ‘b’ and the mileage increase claim is 40% increase I’m always skeptical because all else being equal: you don’t just get hp/watts/energy for free.

[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #11 of 11 Old Today, 05:58 AM
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If you have a catalytic converter, it could be failing and restricting exhaust. Have you chacked the air filter lately? Fuel blend can make a difference although 9 mpg is high. Have you confirmed that the odometer is measuring mileage accurately? Changed tire size or gears since last summer? Is the transmission still shifting into OD? Is the torque converter clutch locking?

Assuming you don't find any actual problems, a good next step might be to look at the data from the engine computer. There are a number of free apps that you can use with either a bluetooth OBDII reader or an OBDII cable. You can't adjust timing externally on an LS so after checking for codes you could watch the O2 sensor for proper activity, check for lean or rich operation, and check to see if the ecm is in Power Enrichment mode during regular driving. Depending on your ecm number there may be free software available that will allow you change the programming yourself. If you're not comfortable making the changes there are a number of tuners that can view data recorded while you drive to make changes to your calibration. Then you can use the free software and the OBDII connection to write the changes into the ecm. This process will take more time than driving to a tuner's shop and driving away with a completed vehicle, but it is likely to be cheaper.
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