Engine Question About Maf And Iac Valve

Discussion in 'Fox 5.0 Mustang Tech' started by Disgruntled3lf, Dec 9, 2013.

  1. How do I do that?
  2. The FMU compensates for the injector size. That's why i say hold off on swapping/buying parts until you read the codes.

    Start from the beginning and see exactly what the ECU doesn't like before throwing parts and money at the problem
  3. Ok. When that scanner comes in should I post here or start a new thread? Should be in 12 Dec. (Thursday)
  4. Clearing codes is correct thing to do first. Then the instinct on just getting that stock maf outta' there is also Top Priority with that power adder....Lol

  5. Well yes. That MAF is not helping either :) It's just way too small and a larger MAF is just added power.
    A5literMan and Grabbin' Asphalt like this.
  6. Start a new thread. Just easier. The scanner is very easy to use.

    Plug it in. Have a buddy sit in the the car, hold clutch pedal in and turn key to on. Then hit the TEST button and let it run through the codes and record them.

    When it's done, have your buddy start the car and still hold the clutch in. The engine running codes should start. Record these. If the car doesn't automatically spit out the engine running codes, turn it off. Restart the car, keep the clutch in and hit the TEST button on the scanner. It should enter test mode and start to spit out the codes to you now.

    When no more codes are displayed, have your buddy blip the gas 1/2 way for a second. This starts the cylinder balance test. let it run through it's think and it will display a number. Write that down.

    Then come back here, start a thread and post up the numbers.
  7. Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

    Dumping the computer diagnostic codes on 86-95 Mustangs

    Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

    Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

    Here's the way 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. You watch the flashing test lamp or Check Engine Light and count the flashes.

    Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

    Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
    Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.



    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.


    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

    89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.


    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

    WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

    What to expect:
    You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

    Some 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.

    Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

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

    Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
    See AutoZone Part Number: 25886 , $10

    Alternate methods:
    For those who are intimidated by all the wires & connections, see Actron® 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 www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader (3145It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
  8. Buy a maf that is calibrated for 30# injectors.
  9. I was under the impression that the FMU only made a difference under boost. It also needs to be calibrated for the injector size. I'd be worried that if the MAF isn't calibrated that the FMU isn't either...
  10. J if you did get a nickel every time you had to post this you'd be rich!! Great info here OP
    Grabbin' Asphalt likes this.
  11. I agree. I share your concerns as well.

    But knowing what codes are stored might help troubleshoot this a bit better. We still need to know more about his combo as well.
    A5literMan likes this.