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  1. #1
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    Brian Rota
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    Default BAD o2? new maf cold air still running rough

    hello
    After dealing with some things last year I put the car away.
    I noticed my original air intake was leaking so I added an ebay air intake kit with a new delphi maf because I was having MAF issues last year.

    The car feels to be running a little rough almost didnt stay running but figured it was learning the maf.
    I checked for codes because the light came on for few with a code 44.
    I did run scan9495 and it appears my MAF is not dumping fuel like the defective maf I had last year.

    The check engine light went off after a little but I didnt check if the code was still there.
    Will a bad O2 sensor make it run rough? I assume 44 is the drivers side? I replaced with a bosch a couple of years ago. Are those o2 sensors good can they go bad with like 1000 miles on it?

    I have attached my scan csv incase anyone can take a look at it and see if something jumps out.
    https://black55chevy-my.sharepoint.c...5nJTQ?e=fLdpl2

    Thank you
    Brian
    Last edited by brota; 05-01-2018 at 10:32 AM.

  2. #2
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    Default

    DTC 44 = Bank 1 (driver side) O2 sensor lean. Could be a faulty sensor, faulty sensor wiring, or could actually be the result of the driver side of the engine running lean.

    What do the long term fuel trims look like for BOTH Bank 1 and Bank 2? I'll look at the log later but don’t have time right now? By looking at both banks, it tells you if there really is a problem only on Bank 1 (indicating a problem that only affects Bank1), or if it’s a problem affecting both banks, but Bank 2 isn’t quite bad enough to set DTC 64 as well.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  3. #3
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    Default

    Capture.PNG

    This is from right when the service engine light came on with car idling

  4. #4
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    Surprised you didn’t get a code for both sides. The LTFT's are maxed out, adding 25% extra fuel to keep it from running lean. Faulty MAF calibration, low fuel pressure, huge vacuum leak, or leak between the MAF and the throttle body, etc.

    Do you have (or have access to) a fuel pressure test gauge? What was the MAF flow in grams/second when code set? Are you sure the rubber connectors for the inlet elbow are tight on the MAF and the throttle body ends?

    I'll try and run through the data log tomorrow morning.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  5. #5
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    Default

    The air pump hose may have been off when I was running the scan.
    I have the new plastic delphi MAF.
    I can test fuel pressure but it was fine last time I tested
    I can verify the tubes are tight. I dont hear I leak I did with factory air inlet that is why I changed it.

    What is the datalogger is that available online?

    Thank you

  6. #6
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    The AIR pump supply hose connects to the inlet air ducting before the MAF. Disconnected hose would pull in unfiltered air, but it would still pass thru the MAF.

    Not sure what you are asking about a “datalogger”. You attached a data log file from Scan9495.... what you called the “scan csv”.
    Last edited by Injuneer; 05-02-2018 at 07:29 AM.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  7. #7
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    Default

    Sorry I misread what you wrote, I thought you said you would run it through a datalogger. I was hoping some software out there that you can parse the log through and tell you what was wrong.
    I do appreciate you looking at this.

  8. #8
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    Never saw a data log with the fuel this screwed up. The problem seems to be worse at low RPM and low engine loads (low LTFT cells).

    On Cell 16 (idle cell), the LTFT's are 160/160 and the STFT's are 194/197 in a typical frame of data. Since the fuel trims are multipliers, in series, the PCM is adding ~89% extra fuel, beyond what it would normally supply = almost DOUBLE. And still the Bank 1 O2 sensor is staying below 200 millivolts. When it stays below that level for 50 seconds, DTC 44 sets. The only reason DTC 64 isn't setting is because the Bank 2 O2 sensor creeps above 200 mV once in a while.

    Either the "new" MAF sensor does not match the the grams/second vs. MAF output frequency (Hz) table in the PCM, or there is a huge amount of air bypassing the MAF. At idle, the MAF (at the end of the log) is reading 4.0 - 4.5 grams/second. The engine is idling at 850+ RPM vs. a target idle speed of 650 RPM in neutral. IAC is fully closed and still can't bring down the RPM. Air is getting there through another path. The MAF reading would typically be a lot higher (as much as DOUBLE) under those conditions.

    The 160/160 LTFT's with high STFT's are still present in Cells 5 and 6. Cell 10 the LTFT's drop to 153/155 with STFT's around 128. When you get on the throttle, and the PCM enters power enrichment mode, Cell 15 LTFT's are only 134/134 (+4.7% fuel) and with the STFT's locked at 128 because its in PE mode, the O2 are reading in the 880 mV range.... a bit lower than you would normally see with stock tuning, but not seriously lean for PE.

    Whatever is causing the problem, the "miscalibration" or the "leak" is limited to lower engine load and throttle positions. I'm still wondering if there is a leak between the MAF and the throttle body. A tear in the rubber coupling, or the coupling being rolled under and not fully on the bottom of the throttle body still seems possible. The leak volume is somewhat limited, possibly even closing up at high air flows.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  9. #9
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    Default

    Another thought - is the hole in the elbow for the IAT fully sealed by the IAT sensor? Do you have a hole in the coupling for the air supply to eh 95's vented Opti system, and is the blue 90-deg elbow in place?

  10. #10
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    Default

    I will look at the sensor maybe that is loose.
    I had to put a small hole in the silicone to for the opti vacuum.

    I know back in the day you could spray gumout to find a vacuum leak is that still true on fuel injected?

    I will go run some more on it

    Thank you

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