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

  1. #16
    Fuel Injected! jim_in_dorris's Avatar
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    What BCC is in the ECM? 92 could have been a 305 bin which would run lean all the time. I know from experience, I fought it for years until I figured out a PO had swapped out the 305 for a 350. Just a thought.
    Square body stepsides forever!!!

  2. #17
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    Quote Originally Posted by jim_in_dorris View Post
    What BCC is in the ECM? 92 could have been a 305 bin which would run lean all the time. I know from experience, I fought it for years until I figured out a PO had swapped out the 305 for a 350. Just a thought.
    The 92 G20 Van I had also did not have a 7747 in it. Had a 299' ECM in it. Almost every 92 I have run across truck/van/suburban/etc had a 299.

  3. #18
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    Also there is always a chance the 7747 does not have a stock chip in it. Could have something from someone like TBI Chips that has ZERO clue what they are doing.

  4. #19
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    I pulled the ECM and took pictures of the label and the prom itself (see attached). The BCC is an ANLW and the exact number is 86ANLW K182590103. My research says this cross references to a prom id of 66 ($42) 91-92 truck 5.7L TBI "K" LO5 w/0 4L80E. Sounds like the right computer for my setup since I have a 700R4 transmission. However, I think it does have a custom prom which is in a socket with a hand written label: HED 350 STK 4-22-04. Please see the attached pictures. I am going to load the ANLW 89 C-G-K-R-V Truck 5.7TBI 700r4 with 2.73 gears.bin file into my TunerPro RT.

    Lee
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    Last edited by bigmac; 03-11-2017 at 10:48 AM.

  5. #20
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    Quote Originally Posted by bigmac View Post
    I pulled the ECM and took pictures of the label and the prom itself (see attached). The BCC is an ANLW and the exact number is 86ANLW K182590103. My research says this cross references to a prom id of 66 ($42) 91-92 truck 5.7L TBI "K" LO5 w/0 4L80E. Sounds like the right computer for my setup since I have a 700R4 transmission. However, I think it does have a custom prom which is in a socket with a hand written label: HED 350 STK 4-22-04. Please see the attached pictures. I am going to load the ANLW 89 C-G-K-R-V Truck 5.7TBI 700r4 with 2.73 gears.bin file into my TunerPro RT.

    Lee
    Definately has a reprogrammed prom chip in it. No telling what changes were made from stock. If you can get your hands on an OEM PROM, I would try running it first after double checking your base timing. I would start with ASDU myself. Does this engine have a smog air pump?

  6. #21
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    No air pump. I will set the base timing later today. Any suggestions on sources for purchasing an ASDU chip? I see a 1227747 ECM with ASDU chip on eBay for $85.
    Lee

  7. #22
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    Quote Originally Posted by bigmac View Post
    No air pump. I will set the base timing later today. Any suggestions on sources for purchasing an ASDU chip? I see a 1227747 ECM with ASDU chip on eBay for $85.
    Lee
    Local junkyard would be my first pick. Look in a 1990+ 350 TBI 1500 truck.

  8. #23
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    I ordered a known good used 1224747 ECM with original factory ASDU chip (see picture below). Should arrive in a few days.

    In the meantime, I attempted to check the base timing. Originally, I didn't see an existing timing pointer so I purchased the Moroso pointer and bolted it to existing timing cover bolts (pain in the butt to install). Only then did I see the existing notched pointer in the center of the timing cover (actually, I could barely see only the right end - the big V notch). I also purchased the nifty device that you screw into the No 1 spark plug hole then tightened the inner screw so the top of the piston will contact it as it comes up on the power stroke. I put a piece of tape around the damper wheel and placed a black line all the way across where the factory line is. I then turned the engine by hand and placed marks where the piston hit the special screw device. I made marks for both the original pointer and the new Moroso pointer. NOTE: the Moroso pointer is about 2 inches to the right of the original V notched pointer. Attached is a picture of the two pointers - you have to look closely to the left of the black Moroso pointer to see the rusty original V notch pointer. And now the fun part: one of the attached pictures shows the comparison of the black marks on the two tapes that were on the damper (the upper tape shows the marks for the original pointer and the lower tape for the new Moroso pointer. Not only are the Moroso marks considerably further to the right, but the distance between the black marks is about twice as wide on the upper tape (original pointer) than the lower tape (Moroso pointer). How can this be? I know the piston was hitting the screw because in addition to me feeling it with the socket wrench on the crank pulley - I had a helper put his fingers on the screw in the spark plug hole and he could feel the it tighten). Also, I marked the half way point between the black marks with a silver line that should represent TDC. Both tapes would indicate that the base timing is way off (maybe 20 degrees). Note, the battery is disconnected so this was a purely mechanical test. Can someone explain which pointer is correct? I think the silver line in the upper tape says the engine is way too advanced, and the silver line in the lower tape way too retarded. I really look forward to someone explaining this mystery to me.

    Lee
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  9. #24
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    I think I maybe figured this out. The piston must be on the Exhaust/Intake stroke instead of on the Compression/Power stroke. I will retest today.
    Lee

  10. #25
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    Quote Originally Posted by bigmac View Post
    I think I maybe figured this out. The piston must be on the Exhaust/Intake stroke instead of on the Compression/Power stroke. I will retest today.
    Lee
    Simce the cam turns 1/2 speed of the crank, TDC is TDC regardless of which stroke you are on.

  11. #26
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    I just did the retest, first turning the engine so top of the piston went around one full revolution before retesting the marks. Now, this comes out near perfect. It looks to me like base timing is about 2 degrees advanced. See attached picture). I assume the computer can make up for this amount. When I get the new computer with the ASDU (should arrive by Friday this week), I will take a new TunerPro log file and post it.

    Lee
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  12. #27
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    I can't follow what you are doing with the piston stop by your description and tape. The stop doesn't stop the engine at TDC so touching the stop and making a mark means nothing by itself.

    You put the stop in and rotate the engine clockwise until it touches and make a mark. Then, rotate the engine counterclockwise until it touches and make another mark. TDC is in between these 2 marks.

    The computer does not compensate for the timing. 2* advanced means the timing is always 2* advanced compared to the programmed timing curves.


    Quote Originally Posted by Fast355 View Post
    If the 02 sensor was cooling off the engine would run rich, not lean.
    When I learned the 1-wire O2 doesn't work in the collector of long tube headers, the engine went badly lean at idle. It would start working correctly again once the rpm's were brought up to the 1500+ rpm range.

    The engine also tended to run a little lean at cruise in the 1500-2000rpm range, but that was a lack of adjusting the loop for the headers since it still occurred with a heated O2 sensor. At cruise I could hear the engine pitch slightly change every time the O2 sensor voltage went low. Some integer delay and O2 switching point adjustments were required to fix it.

  13. #28
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    The procedure you described is exactly what I did. The two silver marks in my picture were the piston stop points. The line I labeled TDC is the halfway point. The other wider black line is the one on the damper. I just guessed that the difference between those two lines is about 2 degrees. Sorry, I didn't make this clearer in my previous description. You make a good points regarding the O2 sensor and the INT adjustments. After I install the new ECM with the ASDU chip later this week, I will retest and see where things stand. If still running lean, then my next plan is to switch the single wire O2 to a 3-wire heated to perhaps compensate for the headers like you stated. If it still is running too lean, then I will probably have to make adjustments to the tables. I will need help doing that but will post the latest log file you to look at first after the above changes. Thanks for the suggestions, I really appreciate them.

    Lee

  14. #29
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    Quote Originally Posted by lionelhutz View Post
    I can't follow what you are doing with the piston stop by your description and tape. The stop doesn't stop the engine at TDC so touching the stop and making a mark means nothing by itself.

    You put the stop in and rotate the engine clockwise until it touches and make a mark. Then, rotate the engine counterclockwise until it touches and make another mark. TDC is in between these 2 marks.

    The computer does not compensate for the timing. 2* advanced means the timing is always 2* advanced compared to the programmed timing curves.




    When I learned the 1-wire O2 doesn't work in the collector of long tube headers, the engine went badly lean at idle. It would start working correctly again once the rpm's were brought up to the 1500+ rpm range.

    The engine also tended to run a little lean at cruise in the 1500-2000rpm range, but that was a lack of adjusting the loop for the headers since it still occurred with a heated O2 sensor. At cruise I could hear the engine pitch slightly change every time the O2 sensor voltage went low. Some integer delay and O2 switching point adjustments were required to fix it.
    2* advanced is 2* advanced over whatever has been programmed into the chip. The chip itself probably has additional advance over stock.

    My experience was exactly the opposite with an unheated o2 sensor in a long tube. The o2 voltage would fall when the sensor cooled off, driving the Integrator and BLM up to their limits. It would run so rich it would actually blow black/grey smoke until the revs came up and the 02 sensor started working.

  15. #30
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    Once I receive the ECM and its stock ASDU chip and get it installed along with a new heated O2 sensor, I will set the timing to 0 degrees (with the ECM wire disconnected). Then I will run the TunerPro software and create a new log and post it here.
    Lee

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