[Uberjeep]

Hey all.
I have been dialing in my homebuilt 4.6l stroker after 2500 kms, and needed a way to figure out if it is running rich or lean as I make adjustments. Not knowing anyone with a wideband o2 meter, and not wanting to spend the money on one for myself, I opted for the poor mans version. I ordered a LCD voltmeter off e-bay for $15 and wired it up to a power source, and tapped off the o2 sensors output to the ECM. Ten minutes of running wires and I now have a gauge that I can switch on at any time to see what is going on in the exhaust pipe. Super handy for making adjustments to my MAP sensor adjuster without having to get out a multimeter, and so much safer than trying to read a miltimeter on the floor at WOT.

As I have been tuning the 4.6l motor I have gotten up to around 18mpg so far which is actually better than the 14mpg I was getting out of the four banger I pulled!!! Who would have thunk doubling the power under the hood would save gas?

Next step is the OBD1 to PC connection. Anyone do this for a 91 inline 6 yet?

[ctm]

Dale B did some work like that years ago for 83+ CJ, link is under Diagnostic Tool:

http://home.sprynet.com/~dale02/list.htm

87-90 YJ has similar diagnostics.

I have used a cheap Summit air/fuel gauge for tuning as well. Tuned the mix so the gauge bounces between min and max (0 and 1 volt), with a good number of bounces per minute (BPM??? ha). I did this for idle and 2500 rpm, and easily passed what was MA emissions testing at the time, they only test ODBII 96+ now.

I'm not sure that the 83-90 "computers" are OBDI ; are they pre-ODB? I think your post is in regards to a 91 engine(fuel injection?) .

So anyway I hope this helps in some way, if not at least for informational purposes.

[the_mork]

As far as I'm concerned these blinky light o2 meters are a waste of money. o2 outputs are non-linear and fluctuate so a momentary reading from a gauge is useless.

The only way to use the narrowband o2 for any sort of tuning is to log the data coming from it in realtime with other engine data such as rpm, injector duty cycle, airflow, etc. I would suggest logging a 4th gear pull all the way to redline then read the data on a graphing display.

If you have an obd1 output check out pocketlogger.

[Uberjeep]

Originally Posted by the_mork

As far as I'm concerned these blinky light o2 meters are a waste of money. o2 outputs are non-linear and fluctuate so a momentary reading from a gauge is useless.

The only way to use the narrowband o2 for any sort of tuning is to log the data coming from it in realtime with other engine data such as rpm, injector duty cycle, airflow, etc. I would suggest logging a 4th gear pull all the way to redline then read the data on a graphing display.

If you have an obd1 output check out pocketlogger.

Of course you can't reprogram fuel curves or anything really usefull on a stock ECM, but when I am working with non-stock fuel injectors, a bored-out throttle body, port matched intake, and upped fuel pressure, the stock ECM is having fun trying to keep up. The O2 reading just points me in the right direction for getting adjustments done.
So far I have built a connector for wiring in to the ALDL under the hood, but no one so far has pointed me to a program that they have used on a PC to log data. I will have a look at pocketlogger though,thanks for the tip!

[Uberjeep]

Originally Posted by ctm

I'm not sure that the 83-90 "computers" are OBDI ; are they pre-ODB? I think your post is in regards to a 91 engine(fuel injection?) .

So anyway I hope this helps in some way, if not at least for informational purposes.

This is indeed a 91 motor (ecm/harness too) bolted into an 89 YJ that had a 2.5l before I got ambitious. All the digging I have done says that the ECM is OBD-1, and I have found the ALDL connector next to the ECM under the hood. My issue comes with what software will let me plug in the laptop and have a chat with the ECM...

[the_mork]

In order to have a chat with the ecm what you really need is a proper cable.

The problem is that you will need a cable that connects to a serial or Com port with a built in translator. Once you've found the proper cable I can point you to all the software that you could need for logging and perfecting your tune.

If the stock ecm is running into problems with the bigger injectors (I don't see how it couldn't) then what are you using to tune it?

Actually I guess the first question is what airflow system does the stock ecm use? I'm assuming it is speed density since I've never seen an MAF on a Jeep. Beyond that then how are you controlling those injectors and how much bigger are they than stock? If you're counting on the o2 sensor feedback to tell the ecm what the injectors are doing and to warn you of danger then I think you are asking for some trouble.

I guess I don't have much of an idea on how you tune Jeeps but I have enough experience tuning Kardon type systems and I understand speed density tuning well enough to know what is going on.

Assuming you know what you're doing I'm really not criticizing you I'm just looking for enough information to understand what I see as potential problems and perhaps enough to guide me along the right path if I feel the need to start modifying fuel systems.

BTW AEM is having a wideband sale and I managed to snatch one up for $205 shipped and I've seen them all over ebay for $218 shipped.

You should be able to use an SAFC to subvert your incoming airflow signal and modify your entire fuel curve that way.

[Uberjeep]

Originally Posted by the_mork

In order to have a chat with the ecm what you really need is a proper cable.
You should be able to use an SAFC to subvert your incoming airflow signal and modify your entire fuel curve that way.

First off I am far from an expert on any of this, so I greatly appreciate all opinions and info, good or bad. I have just been doing a lot of research into it mostly because I am one of those guys who loves to go thru the pain of building everything myself. Secondly I will apologize for the length of this reply, I have a feeling it is going to be big!
I have a custom cable done with a 9 pin rs-232 that is going to plug into an old laptop that is useless for anything else. So far as I have found out, the Chrysler/Jeep SCI type diagnostic port on the 91 harness puts out a signal which can be "read" by various programs, as well as requesting signal data from sensors and the ECM. I can only seem to find one of two things - programs that use OBD2, or programs that are $400 and up. Lol. I will keep digging.

Stock injectors run 19lb/hr @ 39psi high ohm resistance, the replacements are ford slim 26lb/hr(calculated) @ 39psi high ohm. I am running a cold air intake, but even the stock airbox/intake had no MAF or density sensors, so I am super limited in where I can interrupt signals. The fuel delivery is usually controlled by the MAP sensor (along with throttle position sensor, crank position sensor, and manifold temperature sensor), so I am modifying the input voltage to the MAP sensor. Stock is 5.0v I have upped it to 5.1V and got a corresponding change in the O2 sensor voltage at WOT. It was running uberlean at stock voltage (about .17v at WOT) and the bump of .1v brought it closer to ideal (about .35v at WOT) I am continuing to tweak at .01v increments. Before adjusting the input voltage, the new motor would "cycle" at idle. Rpms would creep up by a few hundred, then the air idle control would try to reduce idle speed by closing off, I would hear the whistling in the throttle body, the manifold vacuum would shoot up, causing the MAP sensor to read high vacuum and in turn try to richen the mix, rpms would drop to almost stalling(with super rich smelling exhaust), then the process would repeat. Too lean - too rich - too lean - too rich. Flip the switch to turn on the MAP adjuster and it purrs like a kitten. The stock ECM has adaptive memory as well, so the last 50 warm starts are all used to "adjust" things to compensate for less than ideal conditions. Maybe I shouldn't use the word tuning and should call it re-calibrating with what I am doing. I am not aiming for great 1/4 mile times, I am just wanting to get the ECM to stop fighting the sensors and run as clean and smooth as is possible.
Hopefully that gives a better idea of what I am up to.

[the_mork]

AHA! The program part is easy but I'm going to be late getting out the door.

It also sounds as though the Jeep does indeed use Speed Density, I'll do some searching but I think this can be properly tuned with a few pieces of relatively inexpensive equipment.

I assume that your cycling has a lot to do with the o2 sensor actually being well outside the limits of accuracy.

What you will need to do for the moment I think is focus on bringing your LTFT back to 100%, this should give you a relatively workable street tune.

[the_mork]

Alright, there are a couple of possibilities that I would suggest for logging.

With an RS232 interface you should be able to purchase a palm pilot and use either pocketlogger or the TMO logging software (check google or I can probably find the site for you if you run into trouble). A palm pilot will usually run you about $10-$25 on ebay and will be a much more convenient tool for on the road use.

This is an extremely common setup used for 1g DSMs (eclipse, talon, laser) which are obd1 Chrysler vehicles so it should be about the same as for the Jeep.

There are a number of other pieces of logging software out there but these are tried and true useful programs that will also let you pull trouble codes.

[Uberjeep]

Originally Posted by the_mork

This is an extremely common setup used for 1g DSMs (eclipse, talon, laser) which are obd1 Chrysler vehicles so it should be about the same as for the Jeep.

There are a number of other pieces of logging software out there but these are tried and true useful programs that will also let you pull trouble codes.

Sweet! Light at the end of tunnel! Thanks for the pointers on software, and good call on the palm. The O2 sensor had an unfortunate incident about 2 weeks ago (a sizeable stick poked the O2 wire harness hard enough to yank the wires out of the sensor) so a new sensor was installed.

Now that we are getting into the colder months, I will have lots of time to play with OBD stuff.
Cheers!

[the_mork]

A quick google search also leads me to believe that speed density is indeed tuneable with an SAFC. This cool little device will allow you to select several point along the rpm band and make a custom correction to the airflow at that range with two data sets (high load and low load). At the rpm ranges between your data points it extrapolates a weighted average. They usually cost about $150 used but they might be worth it to have a solid well-tuned setup. Let me know if you have any questions about it or if you want to pick one up. I have one that I would sell and I can point you to a lot of places where they are often found used. It is entirely useless until you get a datalogger though.

[the_mork]

I did a bit more reading and it looks like you may need a more Jeep specific logging program. I'm not sure what you can use but there must be something out there. If you cannot find something then consider the cost of the new o2 sensor you are buying and the cost of your entire engine and consider getting a wbo2 before you do any serious throttle mashing. A new AEM wbo2 is about $210 right now and will give you everything you need to properly tune your system (though without a proper logger it will be a more drawn out pain in the *** process). A narrowband o2 sensor is what? $60 $80? that makes the wbo2 significantly more affordable if you deduct the o2 sensor cost.