Engine Car Wont Rev Past 4/4.5k

Discussion in 'Fox 5.0 Mustang Tech' started by omarimoe, Jul 6, 2014.

  1. A bad TPS does not cause a high speed miss any more that eating green grapes will make your hair purple. The two are not related.
    #41 jrichker, Jul 17, 2014
    Last edited: Jul 17, 2014
  2. You may need a new distributor soon. From looking at the pics of the inside of the distributor cap..it looks like the shaft/pip may have some play causing the spark to bounce around at high rpm.
  3. If you take the cap in your hand and hold it upside down so that you see the contact points, you then take the rotor and hold it upside down and put the center tang against the center button on the cap and look at how far away the rotor tip is to the dist. contact point. It should be less than 1/4" away. If it is further away than that, then the rotor is wrong. I doubt you have this issue what with having purchased 2 new units. It would b e hard to buy the wrong parts twice.
  4. to check the gap i would smash some bubble gum or clay in there and see whats up. looks like too much volts to me. what do your plugs look like? jrich.. how do these cars controll dwell / starting voltage?
  5. The red/blue wire comes from the starter circuit and connects to the TFI. When it the TFI sees voltage on the red/blue wire, it increases dwell time to make a more intense spark. When the engine starts and the key returns to the Run position, the voltage on the red/ blue wire drops and the TFI uses the normal dwell time built into it.
  6. ok i have a weird update. i decided to grab an injector to replace the one i found missing the needle. i ended up grabbing a whole new set from a newer v8 explorer from my buddy (4 holes instead of one). i redid all the vacuum lines and put the intake back on. i started the car and for a while it was surging. come to find out the egr baffle thing must have been leaking aswell because when i disconnected it from vacuum and plugged the line the idle smoothed right out. my problem still did not go away but seems much better. the weird part is now when sitting in neutral if i mat the gas it will rev up past 4k but then comes back down and acts like it's on a 2 step set at 4k. when i take the car out on the road and put it under heavy load i can get past 4k but the second i go wot it does the 2 step thing again. im now thinking this problem may be computer related. im going to see if i can test another computer and see what happens. any other ideas? the only thing left in the ignition system to replace is the pip in the dizzy. i also think im returning my ford racing wires and ordering another set because i got a nice shock when i went to turn the dizzy to adjust the timing. im thinking one of the wires may be arcing off somewhere other than the cap and plug. Also is it normal for one tailpipe to be hotter than the other? Neither are super hot but the drivers side pipe def feels warmer than the other. Has has a cheap sve o/r h pip. The drivers side pipe also feels like it has a tad more flow/pressure. Dont know if im thinking to far into it or not but figured it was worth mentioning.
    #46 omarimoe, Jul 18, 2014
    Last edited: Jul 18, 2014
  7. Dump the codes again and see what you get. There may be some new surprises that weren't there before.
  8. Ill check tomorrow. Today i have a long overdue appointment with the gun range and I dont feel like being irritated with the car lol.
  9. Just a general question because you said the car loses its guts after 4k. Have you done a fuel filter recently cause a clogged one could be a source of your problems.
  10. Car has a brand new driveworks fuel filter that has less than 70 miles on it. I did however notice when I went to move the car today the fuel pump didnt prime when I went to start it. The car started and ran fine while I moved it out of the garage (had to get the mower out). But when I shut it off the pump was making a priming noise and I heard a relay going nuts clicking. Def didnt sound like it was the relay under the seat. Under further inspection I found it to be the relay on the passenger side fenderwell under the cai where the maf is located. Anyone know what this relay is for?
  11. Just an observation but it appears that when you are driving in your video your voltage is running way low at all rpm ranges. I have under drive pullies on my fox body and my car voltage is low at idle then jumps up to well above 13 volts while driving.. Your's didn't move. Not sure how that low voltage would effect your computers ability to adjust parameters but It might be something.. Also.. You changed injectors? Did you have the MAF calibrated properly for the correct injectors you have installed?

    Just throwing my .02 cents out there trying to help...
  12. The voltage guage has never worked since I got the car. Its stuck in that position all the time even when the car is off. The injectors are still 19lb injectors just a newer 4 hole design so the stock maf should not need to be recalibrated. Plus the car has actually run better since the injector upgrade.
  14. On an 89 Mustang with the original factory wiring, the relay under the MAF is the WOT (Wide Open Throttle) relay. It shuts off the A/C compressor when you go WOT.
  15. Since I dont have any of the ac stuff on the car that should not matter correct? Any ideas as to why the fuel pump came on and off a few times after I shut the key off rather then coming on once when I turned the key on? Ignition switch related?
  16. The WOT relay can be ignored if you don't have A/C.

    If the ignition switch is going bad, things like the radio, wipers, turn signals or heater don't work or work intermittently.
    There was a FREE recall on Ford ignition switches. They overheat and sometimes catch fire. That burns up the steering column and sometimes the car interior. Since this is very old information, you may not be able to get the switch replaced for free anymore. The auto parts stores sell the switches for $13-$15.




    Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly

    Read your way through the fuel pump troubleshooter test path. If the ignition switch isn't going bad, the answer is in there...

    Fuel Pump Troubleshooting for 87-90 Mustangs

    Revised 10-Aug-2012 to update fuel pump run time on initial startup

    Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 1-3 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the upper LH corner to ground.



    Turn the ignition switch on when you do this test.

    If the fuse links are OK, you will have power to the pump. Check fuel pressure – remove the cap from the Schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

    No fuel pressure, possible failed items in order of their probability:
    A.) Tripped inertia switch – press reset button on the inertia switch. The hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch

    B.) Fuel pump power relay – located under the driver’s seat in most Mustangs built before 92. See the diagram to help identify the fuel pump relay wiring colors. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.
    C.) Clogged fuel filter
    D.) Failed fuel pump
    E.) Blown fuse link in wiring harness.
    F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect
    for fuel escaping while pump is running.

    The electrical circuit for the fuel pump has two paths, a control path and a power

    The control path consists of the inertia switch, the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the inertia switch (red/black wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (tan/ Lt green wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.

    The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). Notice that pin 19 on the computer is the monitor to make sure the pump has power. The fuel pump has a black wire that supplies the ground to complete the circuit.

    Remember that the computer does not source any power to actuators, relays or injectors, but 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.


    Now that you have the theory of how it works, it’s time to go digging.

    All voltage reading are made with one voltmeter lead connected to the metal car body unless otherwise specified

    Check for 12 volts at the red wire on the inertia switch. No 12 volts at the inertia switch, the ignition switch is turned off or faulty or there is no power to the ECC (computer ) power relay. To be sure look for good 12 volts on the red wire on any fuel injector:
    good 12 volts mean the ECC relay is working. No 12 volts and the ECC wiring is at fault.
    Look for 12 volts on the red/green wire on the ignition coil: no 12 volts and the ignition switch is faulty, or the fuse link in the ignition power wire has blown. No 12 volts here and the ECC relay won’t close and provide power to the inertia switch. Check the Red/black wire on the inertia switch, it should have 12 volts. No 12 volts there, either the inertia switch is open or has no power to it. Check both sides of the inertia switch: there should be power on the Red wire and Red/Black wire. Power on the Red wire and not on the Red/Black wire means the inertia switch is open. Push the button on the side of it to reset it, and then recheck. Good 12 volts on one side and not on the other means the inertia switch has failed.

    Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring, bad ignition switch or ignition switch wiring or connections. There is a mystery connector somewhere under the driver’s side kick panel, between the fuel pump relay and the fuse link.

    Turn on the key and jumper the fuel pump test connector to ground as previously described. Look for 12 volts at the Light Pink/Black wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed, or there is a broken wire in the relay control circuit.

    Pump wiring: Anytime the ignition switch is in the Run position and the test point is jumpered to ground, there should be at least 12 volts present on the black/pink wire. With power off, check the pump ground: you should see less than 1 ohm between the black wire and chassis ground.


    The yellow wire is the fuel tank sender to the fuel quantity gage. The two black wires are grounds. One ground is for the fuel tank sender and the other is the fuel pump. The ground for the fuel pump may be larger gauge wire that the fuel tank sender ground wire.

    Make sure that the power is off the circuit before making any resistance checks. If the circuit is powered up, your resistance measurements will be inaccurate.

    You should see less than 1 Ohm between the black wire(s) and ground. To get some idea of what a good reading is, short the two meter leads together and observe the reading. It should only be slightly higher when you measure the black wire to ground resistance.

    The Tan/Lt Green wire provides a ground path for the relay power. With the test connector jumpered to ground, there should be less than .75 volts. Use a test lamp with one side connected to battery power and the other side to the Tan/Lt Green wire. The test light should glow brightly. No glow and you have a broken wire or bad connection between the test connector and the relay. To test the wiring from the computer, remove the passenger side kick panel and disconnect the computer connector. It has a 10 MM bolt that holds it in place. With the test lamp connected to power, jumper pin 22 to ground and the test lamp should glow. No glow and the wiring between the computer and the fuel pump relay is bad.

    Computer: If you got this far and everything else checked out good, the computer is suspect. Remove the test jumper from the ECC test connector located under the hood. Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer and everything else is connected. Turn the ignition switch to the Run position and observe the fuel pressure. The pump should run at full pressure.
    If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad.
    If it does run at full pressure, the computer may have failed.

    Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn the key to the Run position. This can sometimes fool you into thinking the computer has died. Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin. With the ignition switch Off, jumper the computer into self test mode like you are going to dump the codes. Turn the ignition switch to the Run position. The light will flicker when the computer does the self test routine. A flickering light is a good computer. No flickering light is a bad computer.
    Remove the test jumper from the ECC test connector located under the hood.

    Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the Tan/Lt Green wire has shorted to ground. In extreme ghetto cases, the pump relay may have been bypassed. Remove the fuel pump relay from its socket. Then disconnect the computer and use an ohmmeter to check out the resistance between the Tan/Lt Green wire and ground. You should see more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t jumpered to ground.
    If the wiring checks out good, then the computer is the likely culprit.

    Prior to replacing the computer, check the computer power ground. The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next to the starter solenoid where the wire goes into the wiring harness

    If all of the checks have worked OK to this point, then the computer is bad. The computers are very reliable and not prone to failure unless there has been significant electrical trauma to the car. Things like lightning strikes and putting the battery in backwards or connecting jumper cables backwards are about the only thing that kills the computer.

    See the following website for some help from Tmoss (diagram designer) &
    Stang&2Birds (website host)



    #56 jrichker, Jul 21, 2014
    Last edited: Jul 21, 2014
  17. I borrowed a known working dizzy today and got no change when I swapped them out. The fuel pump thing ended up being a screwy relay so I replaced it and all is well with regard to that. So the list of new and or tested parts are fuel pump, fuel filter, afpr, newer injectors, plugs, wires, cap, rotor, tfi, dizzy, coil, injector o rings, fixed vacuum lines. I cant seem to find anymore wireing problems so the only thing left i can think of is the computer. I didnt get the car with one so I grabbed an a9l from the junkyard. Has anyone ever heard of a computer crapping out in this way? Im about ready to just give up on this car, I have never had any vehicle give me this kind of headache before and its quickly becoming very frustrating.

    This is what the car now does at wot in neutral. You can see as long as I dont have it at wot it revs fine but the second I mat the pedal it acts retarded.

    View: http://youtu.be/-g85Byno3Hg
    #57 omarimoe, Jul 22, 2014
    Last edited: Jul 22, 2014
  18. Video no workie. Did you follow jrichkers advice in his last post?
  19. I think that was in regard to my previous question about the fuel pump priming at funny times. It only happened a few times and went away after I changed the relay. Ill see what f'ed up with the video.
  20. Ran the codes again today. The car is 5spd and has no smog stuff and egr is not connected to anything (just bolted to tb and plugged in).
    85. 94
    85. 44
    12. 33
    From what I can tell non of those codes have anything to do with my problem. It also passed the cycl balance test. Any other ideas? Unfortunately I think I may have to suck up my pride and send it to the stealership or another garage and let them see if they can figure it out.