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  1. #1
    FEP Senior Member dagenham's Avatar
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    Default 91 5.0 quit running

    My wife's stock 91 5,0 LX quit Sunday morning. I'm not sure what's wrong. It has spark but when the key is turned on the fuel pump always primes the system and shuts off. Now the fuel pump keeps running. I don't smell any gas and I don't see any leaks. I have pressure at schrader valve on the right front of the fuel rail but I hear a hissing noise at the same time that I don't recall hearing before.
    And yes there is gas in the tank. But it is less than 1/4 tank.
    Does anyone have any ideas? Also what should the stock fuel pressure be?

  2. #2
    FEP Power Member Ourobos's Avatar
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    Behind the battery one the driver's side fender apron is a big black ground. It's the fuel pump ground. If that is MIA, the pump will continuously run.

    With your hissing, I'm wondering if the regulator may have busted or rotted?

    What were the circumstance for it to quit? Worked great Saturday, Sunday wouldn't start? Or anything done to it right before?

    Also, you said you had pressure at the shrader valve, how much with key on?
    1986 CHP SSP Coupe

  3. #3
    FEP Senior Member dagenham's Avatar
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    It ran last Saturday ok. I have 42 psi with key on and 36 psi while cranking.
    Is the ground the one that has two smaller wires into one eyelet? If so then it appears to be ok. Just verified it is in time also. Unplugged mad sensor at intake tube and no go either.

  4. #4
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    Spray starting fluid into the intake , see if it starts .
    This will verify you have spark , and it is not getting fuel...
    The computer is supposed to prime the pump for 3 seconds then turn it off if the engine is not running .
    clowns to the left of me , Jokers to the right

  5. #5
    FEP Supporter Broncojunkie's Avatar
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    Also see if you are getting power to your injectors. You should also have a ground wire going from the back of the motor (injector harness) to the firewall, iirc. Maybe an orange wire? Been a while since I messed with mine, so I'm not positive. Should be a small ring terminal on it.

  6. #6
    FEP Supporter Broncojunkie's Avatar
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    Also see if you are getting power to your injectors. You should also have a ground wire going from the back of the motor (injector harness) to the firewall, iirc. Maybe an orange wire? Been a while since I messed with mine, so I'm not positive. Should be a small ring terminal on it.

  7. #7
    FEP Super Member sowaxeman's Avatar
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    Less than a 1/4 tank....could it be out of gas and getting faulty reading thanks to an old sending unit, or broken off pick-up...does that happen on these cars?
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  8. #8

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    You should not hear hissing with the key on engine off. You said that yourself. Can you not pinpoint that noise at all? You already said you know it should run 3 seconds and then stop running so your problem is related to that. If the car did not start or no attempt was made to start it everything should just shut back off. So find your hissing sound. If the regulator on the fuel rail is stuck/blown up/whatever they do when they fail, does it pump fuel into the vacuum line connected to it or just send all the fuel back the return? I am not sure on that one.

  9. #9
    FEP Senior Member dagenham's Avatar
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    I pulled the vacuum line off the FPR and it is dry. I hate the thought of it but it sounds like the hissing noise is coming from no. 1 or 2 injector. I'm agreeing with the tank reading incorrectly thought. It never gave any indication before but who knows. Could the noise I hear simply be air being pumped instead of gas thru the fuel rail??

  10. #10

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    Maybe your fuel pump relay is bad or you have a short to ground along the wire from the ecu that triggers the relay. Or a bad ecu. The relay was under the driver's seat but they may have moved it in the last years of the fox
    Or maybe your ignition switch

  11. #11
    FEP Senior Member dagenham's Avatar
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    There's an awful lot of maybes and could be's.

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  13. #13
    FEP Senior Member dagenham's Avatar
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    Can someone show me a pic of the fuel rail or at least tell me which lines are which please? Using the ol hose for a stethoscope method the hissing noise seems louder on the rail without the schrader valve. I am guessing that is the return line?

  14. #14
    FEP Senior Member dagenham's Avatar
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    I only have 11.7 volts at the injectors. Is that close enough or do I need to look for a reason for a voltage drop somewhere?
    I have fuel and I have spark. Run $&@(;: run!!!

  15. #15
    FEP Senior Member dagenham's Avatar
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    Only .20 volts at TPS with key on. Checklist says .5-1.0 volts. Variable by 5%.
    That is just with the key on. Does anyone have the procedure to check it with the key on and moving the throttle? I couldn't find it in the shop manual.
    Last edited by dagenham; 07-22-2017 at 11:33 AM.

  16. #16

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    Closer to 1-volt (0.98v) at idle is ideal. To check it, you do so with the key on, the engine not running, check idle voltage and then slowly open the throttle to wide open, looking to see a smooth progression of voltage increase to wide open, of 4.5-volts. Elongating the TPS's screw holes, so that it's rotationally adjustable at idle (on a good working TPS), is also ideal.
    Last edited by Walking-Tall; 07-22-2017 at 02:55 PM.
    Mike
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  17. #17
    FEP Power Member Ourobos's Avatar
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    ^ correct.. And on the rails, the larger is the feed line, smaller the return line (3/8 and 5/16 I believe). Sounds like possibly a bad TPS.
    1986 CHP SSP Coupe

  18. #18
    FEP Senior Member dagenham's Avatar
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    I guess I'm going to start with a new tps. Only $40. Pissed away more than that to be wrong before.

  19. #19
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    You will need to set the new one aswell.
    .9v or close will be where you want .
    That is with key on in run .
    After the swap, disconnect the battery ground for 30 minutes .
    Then start the car , or try .
    clowns to the left of me , Jokers to the right

  20. #20
    FEP Senior Member dagenham's Avatar
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    Is that to get rid of any lingering code?

  21. #21
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    Correct.
    Anytime you change a part , that you xetermi ed was faulty from a code you had .
    Disconnect the ground for 30 minutes .
    clowns to the left of me , Jokers to the right

  22. #22

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    Check to make sure you are getting 5 volts or close to it on the the vref wire to the tps. Pretty sure it's the orange one. If you don't have near 5 volts, the tps will never read correctly.
    I think you have some larger or multiple problems. Doubt the tps would cause your no start problem or the fuel noise.

  23. #23
    FEP Senior Member dagenham's Avatar
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    Ive decided to ignore the noise I here with the fuel. I have pkenty of fuel flow. I'm in doubt too about the tps but I'm running out of logical things to go on at this point. Plus the low reading I got from it makes me suspicious.

  24. #24
    FEP Senior Member dagenham's Avatar
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    Ok. Tps was a shot in the dark and a miss. Still have the same volt reading as before.

  25. #25
    FEP Super Member
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    Spray starting fluid into the throttle body as i said before.
    This will tell you if this electical or other .
    Engine starts , injectors are not firing .
    No start , no spark .

    Make it easy , before you throw away any more money .
    clowns to the left of me , Jokers to the right

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