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93 Mustang 5.0 Possible fuel issue

edited November 2011 in Repair and Maintenance
I'm helping a buddy with his '93 5.0 mustang. The car wil start but will not stay idling. if the accelerator is gunned, it will run. The car has been tuned up (cap, rotor, plugs, air & fuel filter, also oil and filter). We thought maybe the fuel was old as it had been sitting for a few months so we drained out the old fuel and put in some fresh gas...Still the same issue. Got ahold of a fuel pressure tester from the loaner program at Autozone. The guy behind the counter looked up the spec and said it should be between 35 and 40 PSI. After putting the guage on the Mustang, we got a reading of 30 PSI. Would this reading cause the current issue? Is a new fuel pump in this car's future?
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Comments

  • Key on, engine off fuel pressure should be 35-45 psi. Key on, engine running fuel pressure is 30-40 psi. If the fuel pressure doesn't meet these specs obviously there will be problems. One thing I would try is cleaning the mass airflow meter. Disconnect the connector and let it sit for a few minutes just in case the hot wire is still hot. Remove sensor from housing and spray electrical cleaner on the sensor wires to clean them then let it air dry. Do not use shop air to blow it dry! Reassemble and test. You might also check the fuel pressure regulator by removing the vacuum hose and looking/smelling for the presence of fuel. If you see or smell fuel then the regulator needs replaced.
  • Great Suggestion Pete...Follow his advice Casper.... You may find that your MAF doesnt work AT ALL>...which is causing this issue. Do yourself a favor and go to a U-Pull it Salvage yard and grab one or two of them They are small in size....so You may get out of the yard with a two for one sale if you know what I mean. Where are you located? Do you have any U-Pull it yards?

    You can pull the MAF from ANY 93' Ford V8 5.0L vehicle....those engines all used the same type of MAF....so the Lincoln Continental Mark? had them...the Crown Vic...what else? T-Bird? Mustang Obviously.... Even the FOrd Explorer at one point had the 5 Oh engine I think....so plenty of donor vehicles. I think you will find that MAF to be your issue.....I think that yours mite not be working at all
  • This problem could be caused by any one of a number of things. The fuel pressure is a bit low (pump maybe) but I don't think the problem is due to the pump.

    Possibilities could be, other than those mentioned:
    Vacuum leak.
    Idle Air Valve. (Not a rare problem.)
    EGR stuck open.
    EGR plate gasket rotted out. (On throttle body. Coolant can even leak into intake.)
    Ignition timing way retarded. (Easy to do if ignition module has ever been dinked with as this engine is a TFI model and the SPOUT connector was not considered.)
  • Went ahead and replaced the fuel pump and still in the same situation. I cleaned the MAF sensor with CRC Mass Air Flow Sensor Cleaner and the car idled for a little while (a lot longer than before) but seemed like after a little while, it woud die out but while in the process, it acted like it was trying to stay running. I'm assuming the MAF is bad and needs replacing but I have no Chilton or Haynes manual to get some testing specs. Can the MAF be by-passed? Or maybe some kind of test to determine if it is indeed bad?
  • Still goes back to a vacuum leak or IAC fault in my opinion; all assuming no EGR or ignition timing fault.
  • ALSO....check to see if loosening your Gas cap changes anything....Sometimes they lose their ability to "vent" the tank....and when this happens the cap can create a Vacume situation in the tank.....making it difficult if not impossible for the pump to draw fuel... Just a thought and easy to do...and FREE. Give it a try along with all the other advice
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