'91 5.0 no go. Help!

Discussion in 'Fox 5.0 Mustang Tech' started by txstang347, Aug 9, 2007.

  1. Ok, so I decided to rule everything else out before I deal with how I'm going to take out the TFI for testing. I tested the TPS with an analog meter (all I have at the moment) and I got a reading of 5volts. This is obviously over the 3.7 voltage limit. So what next? Should I replace the TPS or is there a way to recalibrate? Tighten or loosen the screws?

    Waiting on the edge of my seat,
    Joe :eek:
  2. Sure you didn't tap the orange/black wires? thought they got 5v constant from orange wire. If not then ya tps is toast heh
  3. Nope, I tested the green wire. The green wire gave me 5 volts. The other wire gave me a constant 12 volts as expected. I didn't depress the pedal, open the throttle or anything though.

    Should the readings be between .98-.99 volts like I've read on some Mustang sites? Is that the desired voltage and it is just non-operable after going above 3.7 volts? It seems like a big difference from .98 - 3.7 volts.

  4. Just for review...

    Setting the TPS: you'll need a good Digital Voltmeter (DVM) to do the job. Set the TPS voltage at .5- 1.1 range.
    Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere
    between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal
    point on cheap DVM’s is probably fantasy. Since the computer zeros out the TPS voltage every time it powers up,
    playing with the settings isn't an effective aid to performance or driveablity. The main purpose of checking the
    TPS is to make sure it isn't way out of range and causing problems.

    The Orange/White wire is the VREF 5 volts from the computer. You use the Dark Green/Lt green wire (TPS signal)
    and the Black/White wire (TPS ground) to set the TPS. Use a pair of safety pins to probe the TPS connector from
    the rear of the connector. You may find it a little difficult to make a good connection, but keep trying. Put the
    safety pins in the Dark Green/Lt green wire and Black/White wire. Make sure the ignition switch is in the Run
    position but the engine isn't running.

    Here’s a TPS tip I got from NoGo50

    When you installed the sensor make sure you place it on the peg right and then tighten it down properly.
    Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can
    move it just a little in very small increments. I wouldn’t try to adjust it using marks.

    (copied from MustangMax, Glendale AZ)

    A.) Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can
    and get it nice and warm.

    B.) When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the
    lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and
    the other to ground.

    C.) Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull
    the battery lead for 10 minutes.

    D.) The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed

    If the TPs won't adjust below 1 volt, turn the ignition off and measure resistance between the black/white
    wire and battery ground. You should see less than 2.0 ohms More than that is a wiring/bad connection.

    If the resistance test pasess, replace the TPS.
  5. Ok, so I bought a digital volt meter and the TPS tested fine. The analog meter I had wasn't accurate enough.

    The TFI also tested fine at the auto parts store.

    I bought a node light set and there is no flash/injector pulse.

    I put it all back together and tried to start again. Same thing. Fires while starting fluid is in and then dies when it dries up.

    I came to the conclusion that the computer took a crap on me because I've basically tested everything else. I pulled the computer to get the serial # computer code (A9P) and I noticed a relay above the computer. I was told once that there was a relay above the computer and under the drivers seat that control fuel deliver. I've already replaced the relay under the seat so I decided to switch the old relay (assuming it wasn't bad and I don't think that it was because the fuel pump primed and never turned off) with the one above the computer and had the same result, no start.

    So now I'm left with the decision on whether to buy a used computer off of Ebay/junk yard, a refurbished Ford, or a new No name brand from the auto parts store. Anybody have any thoughts on which to buy?

    Is there anyway that the PIP could be the problem and if so how do I test the PIP? Also, I never checked the starter solenoid or the ignition switch since the car starts with starting fluid. Should these be checked before I buy the computer?
  6. TX, I'd re-read the checklist again. It's helpful to step back after diagnostics and do this. I find that I tend to get tunnel vision and miss things when I test on the fly.

    Do your injectors receive constant KOEO 12 volts?

    Was the TPS static reading acceptable (not WOT)?

    If you have spark, your PIP should be ok.

    The relay above the EEC is the EEC relay. It supplies all the engine management systems with VPWR. It sounds like you have spark so yours should be ok (at least part of the VPWR circuit is ok).

    If wanting to toss another puter in, one from a friend's car is always nice. Otherwise, I'd get a J/Y puter.

    Just MHO.
    Good luck.
  7. Do all the injectors not flash the noid light? If so, it is unlikely that the computer is the problem.
    The failure mode for the computer injector circuit is that one or two injectors quit working.

    The one common element to all injectors is the injector power.

    Fuel injectors inoperative, one or more injectors either on all the time or will not squirt.

    Tools needed: Noid light, Multimeter (volts & ohms), 10 MM socket &
    extension, & ratchet.

    Note: Do all of the steps and do them in order. The results of the
    subsequent tests are based on the prior tests being successfully passed.

    1.) Use an ohmmeter set on the low resistance scale and measure the resistance of
    each injector across the two contacts inside the electrical connector. You should
    see between 11-16 ohms. More or less than that is a bad injector. Next measure
    between either one of the contacts and the metal on the injector body. You should
    see greater than 100,000 ohms. Don’t hold the metal probe tips with your bare
    hands when you make this measurement. It will give incorrect results if you do.

    Some basics about the computer:
    Remember that the computer does not supply power for any actuator or
    relay. It provides the ground necessary to complete the circuit. That
    means one side of the circuit will always be hot, and the other side will go
    to ground or below 1 volt as the computer switches on that circuit.

    2.) Get a noid light form AutoZone or other auto parts store, or even better
    a set of them
    This set is from http://www.toolking.com/ProductInfo.aspx?productid=12492 and costs $12.

    3.) Use the noid light to determine that the injector pulses and isn’t
    stuck in the on position. It you have a set of them install all of them and
    compare the pulse intensity. Install the noid lights, turn the ignition switch to
    Run and crank the engine. A light that doesn’t pulse and stays on has a
    short to ground in the computer side of the circuit. That can be either a
    wiring fault or a failed computer. If this is the case, remove the passenger
    side lick panel and disconnect the computer connector. There is one 10
    MM bolt holding it in place. Pull the connector all the way out of the
    computer so that you can see the computer side pins.

    Use the list from the graphic below to find the fuel injector pins for the
    injectors that didn’t turn the noid light off.


    4.) Set the multimeter to low scale Ohms and measure between the
    computer ground located below the computer and the suspect fuel injector
    pins. You should see greater than 100 K Ohms resistance. If you see less
    than 100 Ohms, the wiring between the injector and the computer has a
    short to ground and needs service. Check the harness and look for damage,
    kinks or frayed spots.

    5.) A single noid light that never turns on is either a wiring fault, or a
    failed computer. Either the injector has no DC power or the computer has
    failed and cannot switch the injector circuit to ground. Determine if the
    injector has power by using the multimeter to check for 12 volts on the red
    wire on the suspect injector connector. No 12 volts and you have a wiring fault.
    Check the harness and look for damage, kinks or frayed spots. Check the 10
    pin salt & pepper shaker connectors for bent pins, corrosion and damage.

    If none of the noid lights flash and you have 12 volts at each injector, check
    to see that you have good spark. Before you even think about replacing the
    computer, see step 6.

    Next Check the fuel injector wiring end to end. Each fuel injector has a red
    wire (power) and an non-read wire (computer controlled ground). Set the
    multimeter to low ohms and measure each non red fuel injector wire from
    the fuel injector connector to the matching pin on the computer connector.
    You should see less than 2 Ohms. More than that means a bad connection
    or bad wiring.

    See the graphic for the location of the 10 pin connectors:

    See the graphic for the 10 pin connector circuit layout.

    Once you have determined that the suspect injectors have good power and
    good wiring, the computer is the likely suspect, since a ground is required
    to complete a circuit and make it function. The computer provides the
    ground: if doesn’t, then the noid light will not flash.

    6.) If you have gotten this far, then the problem is likely ignition
    related. Remember the noid test using all of the noid lights? All of them
    were supposed to be equally bright. Since you have already tested all the
    electrical side of the fuel injector circuit, the one remaining common item is
    the pip sensor inside the distributor. A failing pip sensor, damaged shutter
    wheel or bent distributor shaft could all cause the pulse delivered to the
    injectors to be faulty. A bad pip sensor will cause all the injectors not to fire
    and you will have no spark. Dumping the codes will show a code 14.

    7.) Spark plugs indicate one or more cylinders not firing: use the
    multimeter to measure the resistance of the spark plug wires. The wires
    should measure 2000 ohms perfoot of length. A 2 foot wire would be 4000
    ohms and a 3 foot wire would be 6000 ohms. Some Taylor and Accel wires
    have metal cores and will measure much less: that’s OK.
    Next examine the spark plug wires very carefully for burn spots, cracks and
    damaged insulation. One good thing to try is to start the engine while the
    car is a very dark area, open the hood and look for sparks or blue glow.
    They indicate the electricity is leaking out of the spark plug wires.

    Thanks to Tmoss & Stang&2birds at www.veryuseful.com/mustang/tech/engine/ for some of the graphics

    Thanks also to www.fordfuelinjection.com for some of the graphics.
  8. I have your answer!!!!!!!

    I just had the same exact problem. I too have a 91 convertable 5.0. Everything you tried i did. I did some research and come to find out the computer is what gives you injectors pulse. You have a bad computer. If you replace it your problem will be solved but make sure you get the computer that matches the same exact numbers as what is on the one in your car because there are two different. I just picked one up at AutoZone for $97.00 and there was no core so that isnt bad. My car is an LX so my computer number is E9ZF-12A650-CA. I just wish someone had an answer for me when I went through this. Also your fuel pump will work properly after change the computer. Isnt it nice spending all that money when it was the computer the whole time? I know I was pissed!!!!
  9. You would throw $100 or more at the problem for a computer and not $12-$15 for test
    tools and a hour's worth of time? There is something wrong with that picture...
  10. That's my biggest issue. I don't like throwing money and parts at my car only to have it laugh at me and go back to sleep. Although it is nice to know I'm not the only one that the computer has died on msisk14. The biggest problem is that the car is parked 300 miles away at my Dad's and I've been relaying all this info and he's been doing most of the work. I've only been able to go down once to work on it. I know he's about ready to kill me and push the car into the ocean with me in the trunk. :eek:

    I feel like I'm almost there though or should I say "we"...as in everyone who has helped me on this site. Alright I'm not gonna get to congratulatory yet, it still hasn't fired up. I, well I guess I mean my Dad should be able to get to the further computer/injector testing this weekend.

    Oh and we tested two injectors at the time and neither one of them flashed the node light while cranking. More than one of the injectors were tested for power and it was there. There is spark because the car starts and runs strong until the starting fluid dries up. So I'm pretty sure it's the computer, but I've come this far so I might as well run these tests so I can be 100% positive or as close to it as possible.

    *The rest of the injectors were not tested for pulse of voltage because they are really hard to get to without removing the intake.

  11. I understand your point!

    I understand what you are saying about the test equipment but I have already been through this situation and done all the test. He described his problem to the T as to what I had. The only thing that controls the injector pulse is the computer. Even certified mechanics said that they couldnt believe that ended up being the problem. I was just trying to save the guy the time and the money.
  12. She starts!!!!

    Ok, I finally got the car running after all that testing and ruling out parts I only threw one part (fuel pressure regulator) at it before I decided to stop wasting money and figure out what was wrong before I replaced another part.

    I went through jrichker's 6 step checklist and came to the conclusion that it HAD to be the computer. So I decided to go with an Autozone remanufactured Ford because of the one year warranty (Thanks for that little bit of info msisk14). Considering it was only $30 more than what they were going for on Ebay that's not a bad deal.

    Thanks to everyone who reply to this thread over the past couple of months!!!!

    Special thanks to jrichker, HISSIN50, and msisk14.

    Now on to the '90 Bronco II that won't start...haha. Thankfully it sounds like the fuel relay or pump and not electrical/EEC related.

  13. Not sure if this has been checked or if someone already mentioned it ( I scanned the posts and didnt quickly see it ) sorry if it has been mentioned but..........

    Sounds like the distributor module. these are notorious for causing these problems. :mad:

  14. distributor module? pickup coil? sorry you lost me
  15. great thread