car runs like crap when mass ir plugged in

Discussion in 'Fox 5.0 Mustang Tech' started by fastford91, Aug 15, 2006.

  1. i hope someone might be able to help me with this! i have a 91 mustang lx that was stock up untill a little while ago! some of the changes i have made are bored out 30 over to 306, pistons, edelbrock heads , edlebrock upper and lower intakes, cobra svo roller rockers 1:6,75 mm proflow mass air, 70 mm edlebrock throttle body,long tube headers,2 1/2" stainless flow masters,diablo super chip ! the injectors are still stock 19pnds could this be the problem? should i get bigger injectors and recalibrate the mass air and computer ?are the 19lbs injectors to small for this set up ? ive seen cars with less done to them running bigger injectors? ive already tried cleaning the mass air wire with cleaner and it didnt help at all! still ran like **** !! it runs fine when the mass air is unplugged! i know i can pick even more power if the mass air was plugged in,will running it while the mass air is unplugged hurt the motor ? any help here would be welcome ! thank you James
  2. Id step the injectors and mass air meeter up and take it for a tune to get the most efficiency out of the combo..
  3. Unpluggin the MAF should send the computer into Open Loop (the O2's input is not used, and the engine runs on tables).

    You are simply forcing the computer to take a "limp" strategy.

    You need to start by pulling the codes.
    Search here for some posts by JRichker, he has a writeup on how to pull codes without a reader/scanner.
    Or go to AutoZone and they will pull your codes for free.

    It could be that the O2's are shot, or maybe ACT, ECT. I think those are the likely culprits at this point.

  4. Diagnose the problem first, then narrow down the number of things you have to check.

    Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

    Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.


    IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

    Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

    Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

    For those who are intimidated by all the wires & connections, see for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

    Or for a nicer scanner see – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

    Wal-Mart may now have the LCD display scanner for less than $35
  5. step the mass air ?

    the mass air is 75 mm its already steped you think i should go bigger ? i know i should go bigger with the injectors ! but the mass air to?
  6. James-
    Your MAF should be just fine.
    There is a problem however, and that should be fixed as soon as you can.
    I wouldn't bother buying new parts or getting a dyno tune until you have the current setup working well.

    Is the chip you are running setup for all the mods you have? Have you added anything to the car since you bought the chip?

    Pull the codes as JRichker described and let us know what they are.
    There are some very good diagnosis procedures written here.

    Good Luck,
  7. ok ive pulled the codes ! key on engine off test i got 66c, 67c,67o ! key on engine on test 12r , 42 relay and solenoid test 11 everything ok! cylinder balance test 90 everything ok!
  8. oh one other thing when building the motor i used the idle air bypass gasket supplyed with my kit and blocked the idle bypass holes ! could this have anything to do with these problems ?
  9. IF the IAC ports are blocked then the computer has no way of controlling the idle. If the idle setting just happened to be correct then it would just idle a little rough. If the idle setting was off, the car probably wouldn't idle at all.

    Maybe I misunderstood what kit you are talking about, but it seems this is not right.

    Code 42 indicates a rich condition from the right O2 sensor.
    The sensor may be bad or an injector could be stuck open.
    I am not sure how to narrow that down.

    Actually, try swapping the O2 Sensors and clearing out the memory on the computer.
    If the rich condition moves to the other side of the engine, then the O2 sensor is suspect.
    If the rich condition stays on the right side then look for an injector problem.

  10. the kit im talking about was the head gaskets and upper and lower intake gaskets! they came with an idle air by pass plugs to block the holes! i dont know why i put them in and i had doubts before doing it and have had trouble since! it ran fine before i did all the mods and ran great with the mass air plugged in ! but since doing the work and putting those idle air bypass plugs in it wont run good while mass air plugged in! runs fine while unplugged!
  11. Well, the fact that the car runs better with the MAF unplugged does not indicate a problem with the MAF.
    It only indicates that there is a problem with closed loop running.

    Open up the holes in the IAC so that the IAC is functional again.
    Then try swapping the O2's to see if the problem moves to the other bank.
    I think you will make a lot of diagnosing progress that way.
    good luck
  12. ok im going to take the upper & lower intake off and take the plugs out of the idle air bypass and see if that makes a difference! and also put in new o2 sensors! and see what happens
  13. Uh-oh, we may be talking about 2 different things.
    You shouldn't need to remove the upper/lower intake to get to the IAC. Or were you pulling the intake for something else?

    Let us know how things work out for you

  14. I think hes talking about the EGR ports. The EGR not working could cause a lean condition at cruise but I doubt it would effect your idle.
  15. ya we might be talking about 2 different things! when i built the motor the gasket kit for the intakes came with a flat gasket to block the idle air bypass holes in the intake! if my memory serves me correct there were 2 on each side! ( i think ) anyway it hasnt run right since ive done that! so im going to go in there and take them out button it back up and see if that helps! if not ill try the o2's if still not it ill borrow my buddies mass air and plug his in and see if it helps! anyway .... ill let you guys know what happens! its a crappy rainy day here today so im sure ill start it today while im still on vacation! James :SNSign:
  16. You are talking about the EGR ports not your IAC. The EGR ports you blocked would normally channel exhaust gasses into the upper intake and the EGR valve on the back of the EGR spacer would open at cruise. The AIC is that cylindrical thing that sits at an angle on the front side of the throttle body and controls the idle speed.
  17. yes it was the egr ports i was talking about ! i blocked them and thought that this might be the cause of all my problems ! but i took it all apart and low and behold it didnt make a difference! then when i put it back together i found i had an oil leak! so then i took it all apart again and put those egr covers back in ! cause i dont need them cause mine has no polution control on it anyway! but now im back to square one as to what make this thing run like **** when my mass air is plugged in! it ran fine before the mods! im thnking bad mass air! i keep getting a code #66c which says mass air flow sensor fault below minimum votage ? how do you correct this problem? maybe this is the cause for all my stangs heart ache!!!! lol i need to cure her! :bang:
  18. I think it could very well indicate a MAF problem... at startup your car doesn't go into closed loop rigth away. If he gets a good idle /w no maf before it warms up and it idles like poo /w the maf then I would clean or replace the MAF befor anything else.

    I may have missunderstood though, is this a problem that only occurs after the car warms up?
  19. is the MAF calibrated to the right size injectors?
  20. i got the same problem with my 89 lx /w 347 stroker.....plug in mass air flow runs like ****......