Fuel pressure issues
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Junior Member
Joined: Feb 2019
Posts: 4
Fuel pressure issues
I have a 1990 f150 5L. When cold I turn the key, the fuel pump turns on for a few seconds and then stops. I then turn the truck on and it runs great. I go to my destination and stop the truck for a bit. The next time I turn to run position my fuel pump will run for a long time before turning off (meanwhile it reads 40 psi the entire time). It will not start again until the pump turns off. Any idea of what is going on. Why does my pump have to turn off before the truck will fire up?
Super Moderator
Joined: Jul 2006
Posts: 7,555
Not necessarily injectors,,,
The PCM is in control of the timed pump run, (unless a shorted/ closed FP relay) as it would be for suppling the needed injector pulse.
If the pump isn’t timing out/off, could be a relay issue, or PCM concern, but the truck should still start if the pump runs continuously.
If during the time of a no start event if the pump continuous, if the injectors aren’t being pulse commanded, could be the reason it’s not starting.
If you have comp which we know you do,, spec fuel at the rail, hot spark and at the correct time which seems to be a given since it runs well, , injector fuel drop may be missing during a no start.
If during a no start with continued cranking attempts,, a spark plug/s pulled and it proves dry, chances are the pulse is missing..
The PCM is in control of the timed pump run, (unless a shorted/ closed FP relay) as it would be for suppling the needed injector pulse.
If the pump isn’t timing out/off, could be a relay issue, or PCM concern, but the truck should still start if the pump runs continuously.
If during the time of a no start event if the pump continuous, if the injectors aren’t being pulse commanded, could be the reason it’s not starting.
If you have comp which we know you do,, spec fuel at the rail, hot spark and at the correct time which seems to be a given since it runs well, , injector fuel drop may be missing during a no start.
If during a no start with continued cranking attempts,, a spark plug/s pulled and it proves dry, chances are the pulse is missing..
Thread Starter
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Junior Member
Joined: Feb 2019
Posts: 4
It has a tack and does have crank reading. I will find out how to check injector pulse and do a test and reply. My buddy also recommended cleaning both my pump and eec relay (both new) connections as they may be poor. Thanks for the input so far. I have not found any threads on this problem so far. I want to rule out everything before buying new parts. I will post my results. Thanks again
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programguru
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Aug 28, 2009 10:22 AM