1992 Mustang LX 5.0 cranks but won't run...??

Discussion in 'Fox 5.0 Mustang Tech' started by Toddstang LX, Sep 4, 2008.

  1. I drive my car every day and I've never had problems with it cranking or running...until about a week ago. One morning I went to crank it up and it died just as soon as it started...and at the same time the check engine light came on (it has never came on before). I tried over and over to drive it, and it will idle sitting still but dies when I try to drive off. So I can crank it up...and it will just sit and idle as long as it's sitting still. I can get it to drive sometimes for about a block then it will throw a check engine light and just die.

    The weird thing is... I figured out that the car will kind of run without the spout connector in place. When I removed the spout connector the car cranks, but backfires and sputters while I'm trying to drive down the road. AND to make things even more weird... After driving the car while backfiring and sounding like it's running on 4 cylinders for about 15 mins. while the check engine light constantly coming on and going off... the car will all the sudden start to drive like it's supposed to...??? How this happens is beyond my understanding. It has done this over and over as I have had to drive it the past week. I'm afraid that I will destroy my engine or permanently break something if I continue to drive it like this.

    I took it into a shop yesterday and had a diagnostic ran to see why the check engine light came on.

    Here is the list of codes it had stored in the memory:

    I have no idea what these codes mean because the guys couldn't help me and rushed me out of the shop.

    What do the codes mean...and does anyone have a clue what might be wrong with my mustang??

    I'm really frustrated at this point and really don't know where else to turn!

    Any help would me MUCH appreciated!!!
  2. I found my Haynes manual and the codes mean:
    -18:Spout circuit open. <---I know why this one is here.
    -66:No mass air flow sensor signal. <--- Is this bad?
    -87:Fuel pump circuit.<----What does this mean?
    -91:Oxygen sensor problem, fuel pressure out of spec. range.
    -96:Fuel pump circuit.<---Once again??.. Why is there two of them?

    So I know why it's kicking code 18 (because I pulled the spout to be able to drive it) and code 91 is due to the fuel pump circuit problem...I think--> (whatever a fuel pump circuit is??)

    It says in the Haynes manual that a home mechanic can't fix a fuel circuit problem, and I need to take it to a certified mechanic to fix it. Once again.. what exactly is a fuel pump circuit???

    Will the car run with a bad mass air flow sensor? And what exactly is the function of the MAF sensor? And finally...is it important/needed?
  3. Looking at the code dump, it seems like you have fuel pump electrical problems. The pump itself may be OK, but it is losing power. The fuel pump relay and the socket wiring are suspect.

    Code 18 - SPOUT out or wiring fault - look for short to ground in SPOUT wiring going back to the computer. Possible bad TFI.

    The SPOUT enables the distributor to advance the timing beyond the base setting. Without a working SPOUT, you are locked down to the timing you set with the timing light.

    Code 66 MAF below minimum test voltage.
    Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

    There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables.

    The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

    Changes in RPM causes the airflow to increase or decease, changing the voltage output.. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow. Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

    At idle = approximately .6 volt
    20 MPH = approximately 1.10 volt
    40 MPH = approximately 1.70 volt
    60 MPH = approximately 2.10 volt

    Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

    There should be a minimum of 10K ohms between either pin C or D on the MAF wiring connector and ground. Make your measurement with the MAF disconnected from the wiring harness.

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information

    Ignition switch wiring

    Fuel pump, alternator, ignition & A/C wiring

    Computer,. actuator & sensor wiring

    Fuse panel layout

    Vacuum routing

    Code 87 – fuel pump primary circuit failure. The fuel pump lost power while the engine was running. Check fuel pump relay, check inertia switch, wiring to/from inertia switch, red wire going to inertia switch for +12volts. Check the other side of inertia switch for +12 volts.

    To help troubleshoot the 87 code, follow this link for a wiring diagram.
    For 89-93 cars use, http://www.autozone.com/servlet/UiB..._us/0900823d/80/19/59/5a/0900823d8019595a.jsp

    For 86-88 cars use, http://www.autozone.com/servlet/UiB..._us/0900823d/80/16/71/3c/0900823d8016713c.jsp

    Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.

    Code 41 is a RH side sensor,
    Code 91 is the LH side sensor.

    The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

    The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
    "When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

    When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

    Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

    Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

    Testing the O2 sensors
    Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

    Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

    Testing the O2 sensor wiring harness
    Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

    The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

    Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

    If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
    A secondary problem with only a code 41 is for cars with an intact smog pump and cats. If the tube on the back of the heads clogs up the driver’s side, all the air from the smog pump gets dumped into one side. This excess air upsets the O2 sensor calibration and can set a false code 41. The cure is to remove the crossover tube and thoroughly clean the insides to that there is no carbon blocking the free flow of air to both heads.

    Code 96 causes & tests 91-93 models. – KOEO- Fuel pump monitor circuit shows no power - Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits. The fuel pump circuit lost power at one time or another.

    Look for a failing fuel pump relay, bad connections or broken wiring. The fuel pump relay is located under the Mass Air Meter on Fox bodied stangs built after 91. On earlier model cars is under the passenger seat. On Mass Air Conversions, the signal lead that tells the computer that the fuel pump has power may not have been wired correctly. See MAF - Mustang Mass Air Conversion - StangNet - The Mustang Network


    Look for power at the fuel pump - the fuel pump has a connector at the rear of the car with a pink/black wire and a black wire that goes to the fuel pump. The pink/black wire should be hot when the test connector is jumpered to the test position. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. No voltage when jumpered, check the fuel pump relay and fuse links.

    Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92 or later models the fuel pump relay is located under the Mass Air meter. Watch out for the WOT A/C control relay on these cars, as it is located in the same place and can easily be mistaken for the fuel pump relay.

    Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow 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.


    91-93 Models:
    Using the diagram, check the dark green/yellow wire from the fuel pump relay: you should see 12 volts or so. If not the relay has failed or is intermittent. Check the inertia switch: on a hatch it is on the drivers side by the taillight. Look for a black rubber plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the power feed to the fuel pump. Good voltage there, then the fuel pump is the likely culprit since it is getting power. No voltage there, check the Pink/black wire, it is the power feed to the fuel pump relay & has a fuse link in it. Good voltage there & at the dark green/yellow wire, swap the relay.
  4. Wow! Thanks for the help!!:nice:

    Now if I can just figure out what all that means.. I'll be on top of the problem.

    I'm beginning to wonder if my ECU is just bad?...

    BTW....where are the fuel pump relays located?
  5. Swapping the computer is usually a waste of time and money. The computers seldom die.

    On 86-91 cars, fuel pump relays are mounted under the driver's seat.

    On 92-93 cars, the fuel pump relay is mounted on the passerger side fender under the mass air meter. Watch out that
    you don't mistake the A/C WOT shutoff relay for the fuel pump relay. They are similar in appearance. Use the color
    coding on the wires to make sure you have the correct relay. See the diagram I posted to get the wire colors.
  6. Ok... so today I put a new ignition control module on the distributor(had the old one tested and it was BAD). I replaced the mass air flow sensor with a new one. After that I bought a MSD distributor cap and rotor and replaced them as I checked all the spark plug connections (wires and plugs are a few weeks old). Then I found a melted fuel pump relay laying on the passenger side header, just underneath the mass air flow. I thought this was the problem...but I also replaced the burnt relay with a new one...and after all that...


    It didn't make any kind of difference at all... :stupid:

    What should I do now?.. I'm leaning towards a fuel pump issue, but don't want to just replace it for nothing if it's a wiring issue or something like that... How do you test you're fuel pump?
  7. Fuel pump pressure test
    Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not
    have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line
    coming from the regulator. Stick a bolt in the other end of the hose and clamp it. Make sure that
    all your connections are tight and leak proof as possible. Be extremely careful that your
    test connections have no leaks. There is a definite fire hazard when you do this test.

    When this powers up, you don't want fuel squirting everywhere.
    Hook up the fuel pressure test gauge to the Schrader valve pressure test port.

    Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car
    to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC test
    connector and jump the connector in the Upper RH corner to ground.
    Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump

    If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad.
    If the fuel pressure does not hit 55PSI or more in a few seconds, the pump is bad or you have electrical problems.
  8. If the fuel pump relay melted, then there's a chance the wiring to it did as well. Might want to check that next, especially before you go through the hassle of dropping the gas tank.
  9. Well I checked the wiring for the fuel pump and it's not melted or mangled in any way... bought a new fuel pump relay... unplugged and re-connected every sensor I could find on the engine (everything seems to be functioning correctly).

    After that it still idles sitting still like it's supposed to, but when I attempt to drive it. It sputters then stalls and the check engine light comes on... OVER and over again.. And I keep cranking it back up...and if I punch it to the floor... it will light the tires up and run like a scalded dog...but when I slow down to turn or stop for a stop sign... it DIES!:mad:

    UNTIL...it gets to normal driving temp. THEN...it will drive like it is supposed to...???

    So..if I mess with the spout connector...and attempt to keep cranking it back up and trying to drive it... Eventually at mid range temp. it starts driving like it did before it started all this nonsense.

    I'm getting a diagnostic ran on it again tomorrow or the next day...and maybe I'll have a list of new check engine codes to work with....??

    Has ANYONE ever had this problem with their stang before????

  10. Dumping the codes only requires a paper clip...

    Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

    Here's the link 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.

    See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical



    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.

    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.

    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.

    Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

    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 (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
  11. Ok.. I did another test today on my car. I cranked it sitting on a hill...it sat at idle for 10 mins or more. I released the parking brake and as the car started to (very slowly) roll forward the rpm spiked from 800 to around 1300 and the check engine light came on and the engine died. I did this multiple times going forward and reverse. It does the same thing over and over. And just like always...it will sit in one spot and idle till the gas tank is empty. And I was only rolling the car at maybe 3-5 mph on a smooth small incline.

    So.. my question is...what sensor (if any) knows when the car is rolling? Or is there even such a thing?...

    Any help from anyone who might know what is causing this problem would be much appreciated!!
  12. well u said that it runs good wen u hit it... so just run the horsey like a cowboy lol...but seriusly i dont think its ur fuel pump cause ur getting fuel when u punch it but its dieing at idle so i have no idea wats wrong with it
  13. Did you do the fuel pressure test I posted?

    Did you fix the codes?
    The 66 code is a must fix for the car to run correctly.
  14. First off...thank you for all your help guys! I really appreciate all the input!

    And to answer your question Jrichker.

    Yes... I did replace my mass air flow sensor! But I haven't had the diagnostic test done again to see if it's still throwing a code 66. And as for the fuel pump pressure test. I'm not really sure I have the right stuff to do all that....and I really don't think it has anything to do with the fuel pump pressure. It's getting PLENTY of fuel! The melted fuel pump relay was laying on the exhaust header and I replaced it too. I believe it's something completely different.

    Like I said... the car will sit still and idle all day long. I put it in neutral and let it roll forward or backward for a few feet at low speed and all the sudden the engine will idle up (throw a check engine light) and just die. While still rolling it will attempt to crank but will NOT until stopped completely. I even pulled the parking break and shook the car back and fourth and side to side with some help from friends and the shaking motion didn't cause the car to die.

    It is DIRECTLY related to the car being in motion!

    It makes NO sense to me...but I know that whatever it is.. it's driving me CRAZY!
  15. If you expect me to tell you to go buy a $15 part and your troubles will be all over, it "aint gonna happen". You will need to troubleshoot this problem until you find the root source of the problem. Do the diagnostic tests, they are your friend. They will save you time and $$$.

    1.) Clear the codes and then dump them after the engine dies. Compare the results against any codes you may have already seen. List any new codes that are not in your post.

    2.) Put a fuel pressure test gauge on the Schrader valve and monitor the pressure. Most of the auto parts stores will loan or rent a test gauge. In an emergency, you can use a tire pressure gauge to verify pressure. Be aware of leaks from the gauge if you use a tire gauge.

    3.) Check the MAF signal voltage at the computer using the test information in the code 66 test path. You should see the voltages as they are listed in the test path. Try running the car with the MAF disconnected and see if it changes the stall behavior.