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

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    Fuel Injected!
    Join Date
    Mar 2017

    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.

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

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