fastpakr
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V8 Engine Swap
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- Joined
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- 8,106
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- Location
- Roanoke, VA
- Vehicle Year
- 1999
- Make / Model
- Ford
- Engine Type
- V8
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- 285/75-16
I've been helping a friend look at his '91 Pathfinder that frequently takes 10-15 seconds of cranking to start. We put a fuel pressure gauge on it and confirmed that it's not holding any pressure after shutdown. If you're watching a gauge, it drops from ~35-40psi to 0 instantly after turning off the key. We checked the fuel pressure regulator vacuum line and there's no fuel there, so I don't think the diaphragm is ruptured. By holding a long screwdriver to each injector, we confirmed that you can hear each injector cycling - none of them appear to be stuck open.
Based on that, my assumption was that the fuel pump itself might have a bad check valve (we can't see any evidence of external fuel leaks around the lines at all).
However, there's a second issue which is throwing me a little bit... You can only hear the pump prime maybe 10% of the time that you cycle the key to the run position. Every now and then you get a 5 second priming pulse. Most of the time there's none at all. If the priming pulse happens, you can watch pressure build on the gauge to 30 or so and then fall instantly when the pump stops. I can't wrap my head around what would cause the pulse to only happen infrequently like that. There are no obvious issues with the pump relay, and it the pump runs when there are ignition events to keep it turned on.
So... short version:
1) Fuel pressure drops instantly when the pump isn't running. Best guess - bad check valve in the pump.
2) Priming pulse only happens occasionally. When it does, you do see pressure build properly (and return to zero immediately after the pulse).
3) During sustained cranking, pressure slowly builds from 0 up to 35 or 40 over several seconds of cranking.
Thanks in advance for any suggestions!
Based on that, my assumption was that the fuel pump itself might have a bad check valve (we can't see any evidence of external fuel leaks around the lines at all).
However, there's a second issue which is throwing me a little bit... You can only hear the pump prime maybe 10% of the time that you cycle the key to the run position. Every now and then you get a 5 second priming pulse. Most of the time there's none at all. If the priming pulse happens, you can watch pressure build on the gauge to 30 or so and then fall instantly when the pump stops. I can't wrap my head around what would cause the pulse to only happen infrequently like that. There are no obvious issues with the pump relay, and it the pump runs when there are ignition events to keep it turned on.
So... short version:
1) Fuel pressure drops instantly when the pump isn't running. Best guess - bad check valve in the pump.
2) Priming pulse only happens occasionally. When it does, you do see pressure build properly (and return to zero immediately after the pulse).
3) During sustained cranking, pressure slowly builds from 0 up to 35 or 40 over several seconds of cranking.
Thanks in advance for any suggestions!