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  1. #16
    14 PSI Boost Cellos86SVO's Avatar
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    SVO's: 1986 SVO
    I did that before I recorded the video and it holds the pressure no problem. Additionally, when Charlie rebuilt the turbo, he checked it as well and said the actuator was fine. (The turbo has only seen a handful of miles since the rebuild.)
    1986 Mustang SVO
    1988 Mustang GT 'vert

  2. #17
    OVER-BOOST!! GAboySVO's Avatar
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    Acworth, GA
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    SVO's: 2 - 9Ls
    Does it hold pressure over a long period of time? Mine did the same thing. It ended up leaking out of the pinch seam of the diaphragm canister. The small leak is like the bleed port on the manual boost controller and therefore the boost would creep.
    Mike S

    '86 SVO 9L Leather
    '86 SVO 9L Road Warrior
    '96 300ZXTT

  3. #18
    14 PSI Boost Cellos86SVO's Avatar
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    SVO's: 1986 SVO
    What's a long period of time? It seemed to hold pressure fine for about a minute or so.
    1986 Mustang SVO
    1988 Mustang GT 'vert

  4. #19
    OVER-BOOST!! GAboySVO's Avatar
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    SVO's: 2 - 9Ls
    If it holds the same pressure for more then 5 minutes, then I think you can eliminate the WG as the issue.
    Mike S

    '86 SVO 9L Leather
    '86 SVO 9L Road Warrior
    '96 300ZXTT

  5. #20
    14 PSI Boost Cellos86SVO's Avatar
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    SVO's: 1986 SVO
    It's been awhile since I've updated but I decided to live with the boost creep problem for now as I've developed another problem:

    In diagnosing the boost creep problem I was always driving the car at >50% throttle and mainly going around the block. However, in driving it around town at partial throttle (25%-50% throttle), I seem to have some kind of misfire and/or bogging that starts at 2000 rpm but goes away around 3000 rpm. If I press the throttle lightly (<25%) and let it build rpm slowly I don't get the misfire. If I WOT, I don't get the misfire either. Driving around town at WOT, it feels and pulls great. This also only happens when the car is warm. When it's cold there is no misfire/bogging whatsoever. I even recorded a video: https://youtu.be/KjaSYxEI3cc

    I checked for codes but nothing showed up. I checked the TPS and found a dead spot around 3.5 volts so after spending a week tracking down a NOS Motocraft replacement, I replaced it but the issue did not go away. (Before anyone asks, I checked this NOS unit for dead spots and it was good, I installed it and set voltage to 0.95v). I then checked the VAM, no dead spots when sweeping the air volume sensor and the temp sensor read ~3ish volts at 65*. The VAM was a bit dirty so I cleaned it with electronic parts cleaner. I put that back on and no change, if anything it idles a bit smoother now. The plugs, wires, cap, and rotor have been replaced roughly a couple hundred miles ago. The O2 sensor has been replaced with one from NGK. Other than that, I replaced the EGR valve control solenoid about a year ago.

    At this point I'm at a loss of what it could be. Any other suggestions would be welcome at this point. Thanks!
    1986 Mustang SVO
    1988 Mustang GT 'vert

  6. #21
    14 PSI Boost Cellos86SVO's Avatar
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    SVO's: 1986 SVO
    FWIW, I was able to trace the issue to the EGR system. I may have mixed up the vacuum lines at the junction between the EGR solenoid and the signal line to the valve. I've disconnected it for now and it appears to be running great.
    1986 Mustang SVO
    1988 Mustang GT 'vert

  7. #22
    OVER-BOOST!! GAboySVO's Avatar
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    SVO's: 2 - 9Ls
    Glad you figured it out.
    Mike S

    '86 SVO 9L Leather
    '86 SVO 9L Road Warrior
    '96 300ZXTT

  8. #23
    OVER-BOOST!! svono50's Avatar
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    Streamwood, IL
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    SVO's: 86 1C
    Glad you found the issue and reported back too! The EGR system can certainly be the culprit in a lot of driveability issues, but for some reason it is forgotten about and not diagnosed.

    For 'fun' I have transcribed some EGR system info out of the Probst book on Ford fuel injection for reference below. You can see how/when the EGR system can kick in and cause problems, just something to keep handy for future troubleshooting, enjoy.

    ---------------------------------------------------------------------------------------------

    5.1 Exhaust Gas Recirculation (EGR)
    EGR recirculates a small amount of exhaust gas (5 to 15% of intake flow) into the engine through the intake manifold. This dilutes he intake air/fuel mixture and so lowers combustion chamber temperatures (undiluted, as hot as 2500 deg F) to minimize emission of Nitrogen Oxides (NOx) at part throttle.

    The exhaust gasses also warm the incoming mixture, reducing its density and therefore the power output. On some engines, including 1981-85 5.0L, an EGR cooler circulates engine coolant through a spacer between the EGR valve and the intake manifold to reduce mixture temperature.

    The control module only allows EGR when it could not seriously interfere with engine operation. No exhaust gas is recirculated:

    At idle, because NOx formation is minimal and EGR could cause a rough idle.
    During warm-up, because a cold engine is less likely to form NOx, and NOx can interfere with driveability.
    During Wide Open Throttle (WOT), because exhaust gas causes loss of power. Few drivers use WOT for long periods, except perhaps in mountain country.

    The control module operates the EGR valve only when it receives all of the following input signals:

    Warm engine signal from ECT.
    Part-throttle signal from TPS.
    Part-load signal from MAP.
    Time since start, from timer in control module.

    EGR take the place of some of the oxygen in the mixture. So when exhaust gas is flowing, the control module changes fuel delivery and spark timing.
    Ted
    86 SVO Mustang
    17 Cooper S Clubman ALL4

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