Determine if fuel pump is bad by various pressure tests
#1
08-27-2009, 09:26 AM
Determine if fuel pump is bad by various pressure tests
1991 Ford Bronco V8 Four Wheel Drive Automatic 143000 miles
On a cold start, my engine is turning 6-10 times before it kicks up.
I've been hacking away at this issue for about 2 weeks now, and I'll tell you what I have done so far to eliminate possibilites.
1) Changed all my sparks, rotor, and cap.
2) Cleaned battery cables
3) Overnight fuel line pressure test (which stayed in proper PSI range) - maybe I need to do more extensive fuel pressure tests?
4) Replaced fuel filter
I ran a test recommended by a friend. Turned the key to on position, let the pump prime, then off. They did this again, and then cranked up the - it appeared to start normal after this test on a cold start.
So the first assumption was a fuel pressure issue - but it's a bit hard for me to believe the fuel pump is bad if it's priming and getting power OK.
NOTES:
a) Takes only 2-3 rotations when engine is warmed up to fire up (like normal).
b) I've been told this is most likely a fuel pump issue, but I did not want to jump the gun and spend all of that dough until I felt like the issue was really nailed.
Can anyone provide some very specific tests to determine if it's a bad pump or something else?
On a cold start, my engine is turning 6-10 times before it kicks up.
I've been hacking away at this issue for about 2 weeks now, and I'll tell you what I have done so far to eliminate possibilites.
1) Changed all my sparks, rotor, and cap.
2) Cleaned battery cables
3) Overnight fuel line pressure test (which stayed in proper PSI range) - maybe I need to do more extensive fuel pressure tests?
4) Replaced fuel filter
I ran a test recommended by a friend. Turned the key to on position, let the pump prime, then off. They did this again, and then cranked up the - it appeared to start normal after this test on a cold start.
So the first assumption was a fuel pressure issue - but it's a bit hard for me to believe the fuel pump is bad if it's priming and getting power OK.
NOTES:
a) Takes only 2-3 rotations when engine is warmed up to fire up (like normal).
b) I've been told this is most likely a fuel pump issue, but I did not want to jump the gun and spend all of that dough until I felt like the issue was really nailed.
Can anyone provide some very specific tests to determine if it's a bad pump or something else?
Last edited by programguru; 08-27-2009 at 09:28 AM.
#2
08-28-2009, 10:22 AM
What is the problem that you are dealing with? Just the fact that when cold it cranks a while before firing?
If you turn your key to the on position without going to the start position, can you hear the pump priming? If so, the pump is most likely working fine. If it is priming, when cold turn the key to the on position a few times and let the pump prime a number of times before starting the engine. If the engine fires quicker, then your lines aren't keeping fuel pressure and fuel is leaking back into your tank when the pump is off.
If you turn your key to the on position without going to the start position, can you hear the pump priming? If so, the pump is most likely working fine. If it is priming, when cold turn the key to the on position a few times and let the pump prime a number of times before starting the engine. If the engine fires quicker, then your lines aren't keeping fuel pressure and fuel is leaking back into your tank when the pump is off.
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