The Check Engine Light That Makes Me Lose Sleep At Night

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by oldslow89, Jul 4, 2014.

  1. I am new to the forums so please bare with me..

    I have a 1989 Mustang LX 5.0 Convertible 5 speed with 90k original miles. It is my daily driver and the love of my life. Anyways, recently I have had a check engine light that just won't go away. It turns on at start up and stays on until I accelerate a little. If I have my foot on the accelerator, the light goes away, but as soon as I lift it comes back on. Also, up in the higher RPM's (past 4k) the car starts to bog and make noises that downright make me nervous. It sounds like an exhaust rattle from hell. But the exhaust is fine. No leaks or cracks or holes of any kind. It's just a loud chatter.

    Any ideas what could be my problems guys? It just started happening out of nowhere.

    ~old stang

    Attached Files:

  2. If your light is on check the codes, will give you some idea where the problem is. Use the search function, type in dump codes. All you need is a jumper wire or paperclip. Might even be a sticky for this subject.
  3. Do yourself a favor, spend 30 bucks and get yourself an OBD I code reader. great investment and you don't need to wrack your brain counting the bloody flashes.
    90lxwhite, larrym1961 and cdurbin like this.
  4. I have an Innova digital Ford OBD I Code Reader I bought from JC Whitney for about $30. I believe these are an invaluable tool for any EFI Fox Mustang owner.

    jRichker posted about it once and I bought it, great tool to have.
  5. Did you get one?
  6. sounds like your cats are breaking apart and clogging and id replace your o2 sensors also
  7. No but i really should. lol
    90lxwhite likes this.
  8. Here's the answer - cost you 2 cents for a paper clip....

    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 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.