No Get Up And Go (help)

Discussion in 'Fox 5.0 Mustang Tech' started by 90GTFIVO, Feb 24, 2014.

  1. I have a 93 GT that I'm trying to get ready to sell. It's been sitting in my garage and has not been driven hardly at all outside of starting it up and driving it around the block just to knock some dust off.

    Saturday, I finished a tune up (plugs, wires, cap and rotor). Car starts up fine, takes a minute to warm up before it'll idle on it's own. Took it out for a test drive and everything is fine up until between 2500 and 3000 rpm. The car just won't go... acts like it's tied to a tree and really struggles to climb the rpms from 3000 on. I'm at a loss. I was having the problem before the tune up... decided to try the easy inexpensive fix first and it did not solve the problem.

    Here are a few things done to the car before I noticed the problem:
    New clutch and flywheel
    New u-joint
    New starter

    The car does have an MSD ignition box and coil on it. I'm wondering if it's gone bad
    The car also has a battery drain issue, but I don' think that would relate to this issue I'm having
    Old plugs did seem to have quite a bit of gas on them outside of maybe 1 or 2?

    Could it be bad gas? The gas left in the tank is obviously old. Could this be a timing issue? Lastly, I thought I read about a similar problem on here one time and somebody recommended replacing the TFI.

    Any help would be greatly appreciated. Thanks!
    #1 90GTFIVO, Feb 24, 2014
    Last edited: Feb 24, 2014
  2. Pull codes first
  3. 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.
  4. Thanks jrichker!
  5. Bought the digital code reader, hope to have some codes up here this evening.
  6. Wanted to follow up on this thread.

    I tried the code reader, but could not get it to throw anything. The battery may not have been fully charged... not sure if that would have made a difference or not?

    My neighbor is friends with a Ford mechanic that lives a few minutes away. He came over one night to take a look and he ended up adjusting the timing some. I took it down the road and noticed immediate results. Since then I've put a new fuel filter on and with some fresh gas (car has been sitting quite a long time), I think she'll be running pretty good. A few more tweaks here and there by the future owner and I think they'll have a fun Foxbody with some giddy-up!
  7. Bad timing and a clogged fuel filter Will do it.
  8. Try dumping the codes again. If it won't dump the codes, you have a definite problem.

    Computer will not go into diagnostic mode on 91-95 model 5.0 Mustangs

    How it is supposed to work:
    The grey/red wire (pin 46) is signal ground for the computer. It provides a dedicated ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self-test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1 ohm when measured from anyplace on the engine harness with the battery pigtail ground as the other reference point for the ohmmeter probe.

    What sometimes happens is that the test connector grey/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60.

    The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering it to power can produce unknown results, including damage to the computer. The ohm test simply verifies that there are no breaks in the wiring between the test connector and the computer input.

    How to test the wiring :
    With the power off, measure the resistance between the computer test ground (grey/red wire) on the self- test connector and battery ground. You should see less than 1 ohm.


    If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the grey/red wire and pin 46 on the computer wiring connector: it should be less than 1 ohm. More than 1 ohm is a wiring problem. If it reads 1 ohm or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1 ohm. More than that and the computer’s internal ground has failed, and the computer needs to be repaired or replaced.

    See for Joel5.0’s fix for the computer internal signal ground.

    If the first ground check was good, there are other wires to check. Measure the resistance between the STI computer self-test connector (red/white wire) and pin 48 on the computer main connector: it should be less than 1.5 ohms. More than 1 ohms is a wiring problem

    The following is a view from the computer side of the computer wiring connector: it is for an A9L, A9P computer.


    Diagram courtesy of Tmoss & Stang&2birds

    Check out the diagram and notice all the places the grey/red wire goes. Almost every sensor on the engine except the MAF is connected to it.
    91-93 5.0 Mustangs

    Complete computer, actuator & sensor wiring diagram for 94-95 Mass Air Mustangs

    See the graphic for the 10 pin connector circuit layout.

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
    (website host) for help on 88-95 wiring
    #8 jrichker, Jun 7, 2014
    Last edited: Jun 7, 2014
    90GTFIVO likes this.
  9. Thanks again jrichker!