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Thread: Mystified

  1. #1
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    Mystified

    My son's car has me mystified. Some pertinent background:

    1. Car had fully built motor installed, 19Ts and ran great.
    2. After some turbo issues, converted to 16Gs (IPS MHI kit).
    3. During the 16G tune, the tuner noted "all the sensors are jumping all over the place, like the car has bad grounds." Even with MSD coils and HKS DLI, the most boost he could get without ignition break up was 19 psi. But the car made 565 AWHP on pump and seemed to run well other wise. We completely re-worked the battery ground and installed additional ground wires. Car ran reasonably well, no major issues.
    4. When the weather started to heat up, the car began to surge at idle and would often die. It also intermittently "ran like s**t". It also began to surge while driving at low loads.
    5. Yesterday we installed a new stock coil pack, new NGK BKR7E plugs (gapped at .024"), new NGK plug wires and a different PTU.
    6. No help. Starts okay, runs a bit high (1700 or so) at first, then drops to 1100. AF ratio is about 14 for a few seconds. Then it starts to miss, surge from 700 to 1400 RPM and will die if left alone. Because the engine is missing, the wide band reads lean (O2 from mixture not firing). All other indicators (fuel smell, exhaust smoke, etc, etc) say the car is rich.
    7. Now the mysterious part. If I take fuel away by adjusting the fuel pressure regulator down to 24-28psi from the 34psi it should be, the surging all but stops, the miss all but stops and the car will idle without dying. AF stabilizes about 14. Opening the BISS also helps. Both of these make me think the problem is too much fuel.
    8. I left the car with fuel pressure at 28 psi and the BISS one full turn further open than it was when the tuning was done. Car ran "pretty good" on the 5 mile trip from my house to my son's house. He didn't boost it out of concern for fuel delivery.
    9. My wife's car has essentially the same set up and will act up when it's REALLY hot out and the AC is on. But nothing like my son's car. We've previously swapped AEMs and every sensor between the two cars, as well as intake plenums and TBs with no change in either car. His car still runs the same with my pieces and my wife's car runs fine with his pieces.
    10. My car has PTE 660s. His has either PTE 720s or 780s (not sure, P/N is 55598). Could that be the problem?
    Any/all help would be greatly appreciated.

  2. #2
    Twin Turbo verified Feedback Score 5 (100%) GTOJOE's Avatar
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    Sounds like the only thing you haven't swapped is the injectors.
    1990 JDM GTO TT with Vi-PEC plug-in V44 EMS, TD04-13T's, 3SX Downpipe, MP Hi-flow cat, ARC SMIC's, Aeromotive Stealth 340LPH pump, Fuelab 515 FPR, Ninja Performance 75amp hotwire kit, oohnoo fuel loop & rail adapters, Nylon braided ethanol fuel line, NGK AFX Wideband, K&N FIPK, Iridium plugs, HKS Twin Power DLI, Turbo XS racing BOV, 3SX poly mounts, Custom 280km/h speedo.

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    Injector Dynamics 725cc Injectors.

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  3. #3
    Now with more poop-smear Not Verified Feedback Score 8 (100%) IPD's Avatar
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    if it is injectors, you can try using the 720's i've got at my place, milt. that's one quick way you could test it.

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    Thank you for the offer. I'm only wondering if something is failing/has failed and we just haven't thought of it?

    Quote Originally Posted by IPD View Post
    if it is injectors, you can try using the 720's i've got at my place, milt. that's one quick way you could test it.

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    No other thoughts? Anybody?

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    Member verified Feedback Score 0 DocWalt's Avatar
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    Are you sure the fuel pressure gauge is accurate?
    R135
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  7. #7
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    Good question. Short answer: no. But it seems to track. Already changed one Walbro, thinking maybe had a bad pump because fuel pressure dropped under boost. I think the next step is to install a different FPR with a mechanical gauge for comparison. If pressure still drops under boost, then change the other pump.

    Quote Originally Posted by DocWalt View Post
    Are you sure the fuel pressure gauge is accurate?

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    Do you have the O2 feedback on and setup correctly?

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    One day....it will be on 4 wheels. supporter Feedback Score 2 (100%)
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    Stupid question....caps in one of the various ECU's around the car not going?
    Building a House, Car Mods on hold!
    1996 GTO, Owner since 2003.

  10. #10
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    Unless the O2 settings can change on their own they are correct. The car has an AEM standalone, so I don't think there are any caps issues. If all else fails, I'll probably send the AEM back for inspection/repair. But we've swapped out the AEM with the one in my car and the problem stays with my son's car.

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