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Thread: 5.7L running too lean (very high NOx), won't pass state emissions

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  1. #1
    Fuel Injected!
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    5.7L running too lean (very high NOx), won't pass state emissions

    I have an 89 Jeep Wrangler with a 95 Chevy 5.7L TBI crate motor mated to a 700R4 trans. The computer (1227747), wiring harness and all sensors are out of a 92 chevy truck. Since the 700R4 is non-electronic, it has the 1227747 computer. This setup was installed in 2000 but it only has about 8,000 miles on it since the vehicle was primarily used for off-road. The main problem is NOx are very high around 1300 (max allowed is about 800). California does emissions testing at 15mph and 25mph which is about 1600rpm on this vehicle - so part throttle. High NOx means the combustion chamber is running way too hot because the engine is running too lean. I had a certified mechanic check it out a few months ago. He thoroughly checked the EGR components, no vacuum leaks, TPS and other sensors, timing, replaced O2 sensor, replaced coolant temp sensor (the one that feeds the ECM), new catalytic convertor, switched fuel canister & purge system from Jeep to Chevy, etc. Engine starts right up, idles fine, and has plenty of power. Also, replaced P/N switch and wired it with a new starter relay so ECM B10 get a ground if shifter in P or N. So, I purchased the Moates Extreme ALDL hardware and cables and TunerPro RT (using $42-1227747-V5.2.adx). Data is streaming fine and I have attached my XDL file which shows cold engine through normal operating temperature (about 200 degrees). I am new to reading the TunerPro RT results, but it looks to me like the ECM goes into closed-loop mode when the coolant reaches about 115 degrees, BLM holds pretty steady around 128 but occasionally goes into low 130's. I did notice that once fully warmed up and at part throttle, the O2 sensor output seems to be quite low (100mv or less) and the Rich/Lean parameter pretty much stays Lean - event hough the BLM remains steady at 128. I don't quite understand this. So, can someone take a close look at my attached XDL file and perhaps explain what is going on? I haven't measured the fuel pressure since it is a pain to get to the metal line under the rear of the throttle body with the engine crammed in a Wrangler.

    Lee
    Attached Files Attached Files
    Last edited by bigmac; 03-10-2017 at 06:47 PM.

  2. #2
    Fuel Injected! uncabob's Avatar
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    Hi bigmac:
    Just curious about your O2 sensor: Is it a heated sensor? Is it located in or near the manifold or collector? Do you have headers or cast iron manifold?
    What size exhaust pipes and are they dual going into a Y or crossover? One cat or two?
    Bob

    ps Didn't look at your .xdl.
    Last edited by uncabob; 03-09-2017 at 07:54 AM.
    Don't force it, get a bigger hammer!

  3. #3
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    O2 is single wire (non-heated). It is located in the rear of the passenger side ceramic header (just above the collector area). Driver side exhaust connector pipe runs under oil pan to a y-collector on passenger side. A single 3" diameter exhaust pipe runs from the y-connector to a new cat then to a muffler then over the rear Dana60 axle terminating under the bumper.

    Lee

  4. #4
    Fuel Injected! uncabob's Avatar
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    May not be getting hot enough? If nothing else is obvious you may want to go to a heated sensor.

    Bob
    Don't force it, get a bigger hammer!

  5. #5
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    Thanks Bob. I will look into converting to a heated O2 sensor.
    Lee

  6. #6
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    If the 02 sensor was cooling off the engine would run rich, not lean. I would check your base timing and make sure it is set for TDC or 0*BTDC. Also check the base fuel pressure the engine is running at. These engines like to be in the 12-13 psi range even with a stock engine. Maybe as much as 14 psi with a higher flowing intake/exhaust setup. Finally check your injectors to make sure that you have the 61 lb/hr injectors, not the 46s or 55s from a 4.3 or 350. I would also suggest that dropping the coolant temp will help prevent the formation of NOx emissions. A 180*F thermostat will drop the numbers some as well.
    Last edited by Fast355; 03-09-2017 at 10:48 AM.

  7. #7
    Fuel Injected! De-stroker's Avatar
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    I cant open your file so im just stabbing, that engine is gonna run cold if the air gets under it, my 5 speed trucks' oil got so cold that it lost a rod bearing it was always at 1500-2000 when it was running I don't think you have a computer issue, U will be able to tell if the injectors are firing right. does it spray consistently through the rpm? Not saying that's an easy issue you have.
    Last edited by De-stroker; 04-11-2017 at 06:49 AM.

  8. #8
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    I don't think this is part of my problem as the engine actually runs on the hot side - probably because it is mounted in a Jeep Wrangler, I live in a warm climate, and don't go 4wheel'n in the snow during the winter months. But I will check the injectors spray pattern across RPMs.

  9. #9
    Carb and Points!
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    There is a lot more experience in this thread than I have, but I will toss something out I ran into.

    My suburban started running bad and I could see it in the data log it was running extremly lean and it was obviously much worse than yours is. I finally traced it down to one of the injectors being badly clogged and it wasn't flowing enough fuel. It was so bad you could see that one side wasn't like the other side. Both injectors were probably dirty and running lean, just one was really bad! I bought two new units and that fixed mine, if the chip doesn't fix that you might have dirty injector(s).

  10. #10
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    Lack of fuel would definitely cause it to run lean. As soon as I get my computer back, I will carefully check the spray pattern. Moates is replacing the 24 pin socket and soldering in a new 28 pin socket. Once I get it back, I will drop in the ARJU (California) chip then check everything out.

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