94 cobra run rough, cuts off, but runs a little better with MAF unplugged

Discussion in '1994 - 1995 Specific Tech' started by webshot, Mar 23, 2013.


  1. toyman

    toyman SN Certified Technician

    Joined:
    Jul 20, 2007
    Messages:
    1,839
    Likes Received:
    41
    Trophy Points:
    49
    Location:
    Vernon BC
    Let's assume it's fuel related. First you need to test for fuel pressure and if it's not to spec possible causes are: bad fuel pump, clogged filter or a failed regulator. Do the easiest first. Filter, replace if you don't know how long it's been in use. FPR, remove the vacuum line. If there is any hint of gasoline it needs to be replaced. To confirm the fuel pump the first two possible causes need to be verified as being good. Fuel pump needs to be tested KOEO and KOER. KOEO should be about 40 psi. KOER about 35 psi.
     
    #21
  2. webshot

    webshot Member

    Joined:
    Sep 11, 2005
    Messages:
    729
    Likes Received:
    0
    Trophy Points:
    17
    Location:
    Yay Area, California
    Thanks Toyman, I will test fuel pressure tomorrow. I gotta run out and grab a fuel pressure gauge (and look up a how to to do this as well). I have a couple questions about the next couple items fuel filter and FPR. Mainly where will I find them on the car.

    Thanks man
     
    #22
  3. webshot

    webshot Member

    Joined:
    Sep 11, 2005
    Messages:
    729
    Likes Received:
    0
    Trophy Points:
    17
    Location:
    Yay Area, California
    You wouldnt happen to have a write up on checking fuel pressure? Searching now but cannot find one.
     
    #23
  4. revhead347

    revhead347 I have face herpes.

    Joined:
    Jun 14, 2004
    Messages:
    6,615
    Likes Received:
    286
    Trophy Points:
    124
    Location:
    Acworth, GA
    There is a schraeder valve on the passenger side front of the fuel rail. You hook a fuel pressure gauge in there when the car is running. Should be around 35-38 psi at idle. As long as it's close the car should run fine. If it's like 60 psi you have a problem.

    Kurt
     
    #24
  5. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

    Joined:
    Nov 30, 1999
    Messages:
    8,439
    Showcase:
    9
    Albums:
    1
    Likes Received:
    1,225
    Trophy Points:
    174
    Location:
    a van down by the river
    or 20 LOL
     
    #25
  6. webshot

    webshot Member

    Joined:
    Sep 11, 2005
    Messages:
    729
    Likes Received:
    0
    Trophy Points:
    17
    Location:
    Yay Area, California
    I was reading where some folks where taking a pressure reading when starting the car too. Do I need to do a reading when cranking? Also the only real way the car stays running is with the MAF unplugged. Is it ok to test that way?
     
    #26
  7. revhead347

    revhead347 I have face herpes.

    Joined:
    Jun 14, 2004
    Messages:
    6,615
    Likes Received:
    286
    Trophy Points:
    124
    Location:
    Acworth, GA
    Once you turn the key to the on position and hear the fuel pump it should come right up to pressure. It actually isn't necessary to start it up.

    Kurt
     
    #27
  8. toyman

    toyman SN Certified Technician

    Joined:
    Jul 20, 2007
    Messages:
    1,839
    Likes Received:
    41
    Trophy Points:
    49
    Location:
    Vernon BC
    Well it is important to check the pressure while running so as to ensure the pressure is being maintained.
     
    #28
  9. 02 281 GT

    02 281 GT Active Member

    Joined:
    Feb 3, 2009
    Messages:
    396
    Likes Received:
    25
    Trophy Points:
    39
    Location:
    Kusel, Germany
    This is going to sound silly, but did the previous owner install an SCT switch chip? I have on installed on my car. When I took it to the body shop, it somehow got switched to one of the non-running positions and behaved exactly as you describe (turns over, barely cranks up, requires heavy gas pedal application to stay barely running). Turned it back to one of the tune positions and it ran perfect.
     
    #29
  10. revhead347

    revhead347 I have face herpes.

    Joined:
    Jun 14, 2004
    Messages:
    6,615
    Likes Received:
    286
    Trophy Points:
    124
    Location:
    Acworth, GA
    Yeah that's true, but if you can't get it running that's a start.

    Kurt
     
    #30
  11. earleys94gt

    earleys94gt Active Member

    Joined:
    Aug 31, 2003
    Messages:
    1,217
    Likes Received:
    16
    Trophy Points:
    49
    Location:
    Ashley, Ohio
    Code 564 is low fan circuit relay, check the relay as well as the grounds in the engine bay...sometimes a wire brush can clean all the crap off of the grounds.

    You said before the car has been sitting, and that got me to thinking if something like bad gas could/is the problem or adding to it??
     
    #31
  12. webshot

    webshot Member

    Joined:
    Sep 11, 2005
    Messages:
    729
    Likes Received:
    0
    Trophy Points:
    17
    Location:
    Yay Area, California
    02 281

    I am not sure what that is, how do I check that?

    Hey guys it was raining pretty tough over here and with the holiday I have not had a chance to check into the fuel pressure. But let me ask you this. I got in contact with Pro-M and explained my MAF sensor issue with their CAI kit. ANd they guy told me that there is no OEM replacement MAF for 24lb injectors? Basically he said I will need to buy a new kit, which is this http://www.promracing.com/mass-air-meters/75mm-plastic-bullet-un-flanged.html . Does that sound correct?

    This is the replacement MAF I purchased.
    http://www.autozone.com/autozone/pa...48upZ9gsmv?itemIdentifier=267297_298837_4995_
     
    #32
  13. 02 281 GT

    02 281 GT Active Member

    Joined:
    Feb 3, 2009
    Messages:
    396
    Likes Received:
    25
    Trophy Points:
    39
    Location:
    Kusel, Germany
    Remove the passenger side kick panel (panel in front of the door, just below the dash). You'll see the PCM (engine computer) mounted underneath it with the connector on the top side slightly out of view. On the bottom side of the PCM will be a test port with a small plastic cover. If there is a wire protruding from the test port, then the PO likely installed a switch chip. A switch chip is basically just a chip with different engine tunes burned onto it which is installed into the test port connector. Which tune is currently active is controlled by a small 8-position rotary switch connected to the chip at the PCM via a long cable. Positions 1 through 3 are usually the tune positions, 4 is the stock tune, and all others are usually non-running positions.

    They're technically correct in that there is no Mustang-specific stock 24lb injector MAF sensor. The Cobra-specific computer compensates for the 24lb injectors. All 1994-1995 Mustangs had the same MAF sensor; it was also found on a lot of other Ford vehicles. Check out this post for a list of which vehicles: http://www.stangnet.com/mustang-forums/threads/need-help-with-maf-coversion.823903/#post-8294825
     
    #33
  14. webshot

    webshot Member

    Joined:
    Sep 11, 2005
    Messages:
    729
    Likes Received:
    0
    Trophy Points:
    17
    Location:
    Yay Area, California
    ok tested the fuel pressure 38lbs with key on, 38 when car is idling.
     
    #34
  15. webshot

    webshot Member

    Joined:
    Sep 11, 2005
    Messages:
    729
    Likes Received:
    0
    Trophy Points:
    17
    Location:
    Yay Area, California
    I hate to start throwing parts at this thing, but after some research I am seeing some people reporting issues like mine. This is not the same year but I have a similar issue.

    "

    I had a run condition just like yours with a 92 . It would not idle with the mass air conected and if you pedaled it it would pop and miss fire in the intake . Tried everything from mass air to computor . Pulled a vac line and it ran better but still crappy . Turned out to be an injector problem . I think one or more were stuck open . When the mass air was pulled the limp mode would let it lean a bit an run . It might not be the problem but something else to look at .

    "

    How do you test injectors? Mine is doing the same thing with the MAF plugged in.
     
    #35
  16. toyman

    toyman SN Certified Technician

    Joined:
    Jul 20, 2007
    Messages:
    1,839
    Likes Received:
    41
    Trophy Points:
    49
    Location:
    Vernon BC
    You can test if they are firing with a node light. As to flow they may need to be pulled. Before doing that I would run some injector cleaner through them first. Also there is a system that allows you to clean injectors without removing them. Some shops will have the equipment to do this.

    Anyone notice that the avatars are upside down today. Must be an April 1st thing.
     
    #36
  17. webshot

    webshot Member

    Joined:
    Sep 11, 2005
    Messages:
    729
    Likes Received:
    0
    Trophy Points:
    17
    Location:
    Yay Area, California
    Ok I will look into testing my injectors as well as running some injector cleaner through them. Also I forgot to mention that I have a ton of powder coated parts under the hood (upper/lower manifold, valve covers, accessory brackets..). It was recommended that I check the grounds too. I will be doing that this week as well. Will report back....

    Also quick question, the "node light" you speak of is that a normal test light? I am guessing I will touch the terminal on the top of each injector, turn the car on and see if it lights up? Sorry most of this i have never done before. Does anyone have a write up for doing this?

    Thanks
     
    #37
  18. Venom351R

    Venom351R Founding Member

    Joined:
    Apr 27, 2002
    Messages:
    13,944
    Likes Received:
    36
    Trophy Points:
    98
    Location:
    MAINE
    111 is a system pass code. 564 is an electro fan drive circuit fault.
     
    #38
  19. toyman

    toyman SN Certified Technician

    Joined:
    Jul 20, 2007
    Messages:
    1,839
    Likes Received:
    41
    Trophy Points:
    49
    Location:
    Vernon BC
    Just google it for instructions/video. You can make the node light using a LED bulb.
     
    #39

Share This Page