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Thread: Custom build 1990 Mustang stock injection need help

  1. #1
    Carb and Points!
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    Custom build 1990 Mustang stock injection need help

    Hello all i am new to the site. I didnt know if i should of posted this in the Gm or Ford section but being the injection is from a 1990 mustang i will give this a shot.

    Ok my build. 1984 Pontiac Fiero. Motor is a 1993 Cadillac 4.9 complete from pan to intake. Fuel injection is from a 1990 Ford mustang HO 5.0/302 from throttle body (custom plate made to fit GM intake) down to a new computer system.

    Funny build huh? Well anyhow it works! But I am having a small issue that I want to get rid of. So far all the sensors are brand new and been replaced but the mass air flow. The issue are the idle. It dont like to idle the same every time. Most of the time when I come to a red light or stop sign the idle drops so low it stalls. To keep it from stalling i put it in neutral and when i take off I have to give it a small amount of gas and put into gear. It almost sounds like I put a 480 lift cam in it sometimes carrying on jumping and what not. It never blows black smoke. Also when going down the road it loses power! I know for a fact it has to do with the fuel system because that's what it feels like. It feels it don't get enough fuel some times.
    I think it might be the mass air flow but I don't want to spend $200 and that not be the problem. I have a video on youtube called Ruffy,s V8 fiero throttle body and computer for a small look.

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    wow, that is an odd combination of parts...

    seeing that it's run by the ford computer, this is the correct section.

    you have any way of datalogging it to see what's going on in the near-stall conditions?
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  3. #3
    Carb and Points!
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    No I dont. I wish I had the extra money to get a tool to tell me the error's that's going on.

  4. #4
    Fuel Injected!
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    yeah ditch the EEC and grab a 7730 lmao. jk. ever tried EECtuning.org?

  5. #5
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by Ruffy View Post
    No I dont. I wish I had the extra money to get a tool to tell me the error's that's going on.
    Most auto parts stores will do that for ya...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  6. #6
    Fuel Injected!
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    Some questions. What is your fuel pressure? What injectors? What EECIV manual (A9L) or auto (A9P) or something else? Is it a manual or auto tranny? Do you have a VSS wired in?
    If you are using a manual ECU with an auto tranny and no VSS you will get those stalling issues like you described. I had this issue when I switched over to an auto tranny. I switched to the auto EECIV and it worked good with no VSS. It still idles down pretty far when coming to a stop but doesn't stall. This is on a 5.0 though. How did you get the pip signal from the caddy ignition?

  7. #7
    Fuel Injected! jameslleary's Avatar
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    You can pull codes with a paper clip or jumper wire. You can also use a test light in place of the VOM. This diagram is from the Charles Probst book:
    And, may be a stupid question, but did you modify the Injector harness to acommodate the Caddy firing order? Also, make 100% sure that you have the Hegos on their correct banks? Questions from my past experiences, I started on mustangs. Also, did you pull the system from a mustang, or is it a set up that you bought from someone...there are 2 firing orders for ford 302's.

  8. #8
    Super Moderator Six_Shooter's Avatar
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    Firing order of a 302 won't effect how a Caddy 4.9 runs. ;)
    The man who says something is impossible, is usually interrupted by the man doing it.

  9. #9
    Fuel Injected!
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    Quote Originally Posted by Six_Shooter View Post
    Firing order of a 302 won't effect how a Caddy 4.9 runs. ;)

    even though the EEC has sequential injector pulses?

  10. #10
    Super Moderator Six_Shooter's Avatar
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    Quote Originally Posted by 34blazer View Post
    even though the EEC has sequential injector pulses?
    To me "firing order" is ignition side.

    "Injector order" is different. ;)
    The man who says something is impossible, is usually interrupted by the man doing it.

  11. #11
    Fuel Injected! jameslleary's Avatar
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    Quote Originally Posted by Six_Shooter View Post
    To me "firing order" is ignition side.

    "Injector order" is different. ;)
    Fine, Injector order...nit picker!

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    EFI GearHead ! EagleMark's Avatar
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    The SFI may effect idle or could be turned off, not sure how newer cars work but the LT1 is only SFI in idle very low RPM, then batch fire. Just not enough time to fire each injector at higher RPM with cars of this era.

    Are newer cars sequential at more then idle RPM? I was told that idle emmisions was only reason for this at time, had no impact on drivability or performace cause there's just not enough time to turn on/off injector for each cylinder.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Quote Originally Posted by EagleMark View Post
    The SFI may effect idle or could be turned off, not sure how newer cars work but the LT1 is only SFI in idle very low RPM, then batch fire. Just not enough time to fire each injector at higher RPM with cars of this era.

    Are newer cars sequential at more then idle RPM? I was told that idle emmisions was only reason for this at time, had no impact on drivability or performace cause there's just not enough time to turn on/off injector for each cylinder.
    don't suppose you can throw 2 injector circuits on a scope and confirm this? seems odd that it would switch out. my 95 MC should be SFI at all times, but i don't have a scope to confirm it.

    i made a thread on 60V6 about the differences in single fire MPFI, double fire MPFI and SFI.... it wouldn't bother me one bit if SFI had yet to be invented.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  14. #14
    Super Moderator Six_Shooter's Avatar
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    From many years of SFI discussion it seems that most manufacturers switch between SFI and batch fire at around 3000 RPM.
    The man who says something is impossible, is usually interrupted by the man doing it.

  15. #15
    EFI GearHead ! EagleMark's Avatar
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    There is a Constant in TunerCat $EE I do not have in TunerPro $EE which would tell us when it happens in an LT1 called :

    "Individual Cyl. Fuel Trim Disable %TPS"

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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