You can put a live jumper lead on the relay tag. If the pump works the problem is (electrically) upstream. If it doesn't, then it can still be the downstream wiring. A poor ground wire on my truck gave the impression of a failed pump....
The 98 5.7 fuel pump no worky.....
- Thread starter Wilecoyote
- Start date
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Given a choice--and not everyone has this choice--I won't replace a fuel pump without checking:
1. Voltage as near the pump as I can conveniently test, with the pump RUNNING. Test the positive wire, AND the negative wire. Typically, at the most-rearward wire harness connector before the wiring disappears into the tank. VOLTAGE has to be tested at or near the load. Of course, if the pump won't run, you test for voltage anyway. If voltage is acceptable with the pump running, the wiring is "probably" OK.
2. Pump amperage draw with the pump running. Typically 5--6--7 amperes. If the pump won't run, it may be shorted and still drawing current, so the test is worthwhile.
3. If possible, I test amperage using a "low amps" inductive probe, and an oscilloscope. I can then verify the amperage of EACH BAR of the electric motor's armature, compare them to each other. I "see" that there isn't one or two bars of the armature giving problems. I can count the number of armature bars, and using some mathematics, verify the pump RPM.
If RPM, Voltage, Amperage, and equality of armature bars is good--but the pump doesn't produce volume, or pressure like it should--I know that either the pump is bad, or the filter/sock is plugged (which means the pump is probably wounded.)
If the electrical part of the pump and power supply circuitry doesn't test good, that has to be repaired before the actual pump can be diagnosed.
1. Voltage as near the pump as I can conveniently test, with the pump RUNNING. Test the positive wire, AND the negative wire. Typically, at the most-rearward wire harness connector before the wiring disappears into the tank. VOLTAGE has to be tested at or near the load. Of course, if the pump won't run, you test for voltage anyway. If voltage is acceptable with the pump running, the wiring is "probably" OK.
2. Pump amperage draw with the pump running. Typically 5--6--7 amperes. If the pump won't run, it may be shorted and still drawing current, so the test is worthwhile.
3. If possible, I test amperage using a "low amps" inductive probe, and an oscilloscope. I can then verify the amperage of EACH BAR of the electric motor's armature, compare them to each other. I "see" that there isn't one or two bars of the armature giving problems. I can count the number of armature bars, and using some mathematics, verify the pump RPM.
If RPM, Voltage, Amperage, and equality of armature bars is good--but the pump doesn't produce volume, or pressure like it should--I know that either the pump is bad, or the filter/sock is plugged (which means the pump is probably wounded.)
If the electrical part of the pump and power supply circuitry doesn't test good, that has to be repaired before the actual pump can be diagnosed.
Wilecoyote
I'm Awesome
The pump has been whining loud for months at idle and it gets louder w the throttle. A few weeks ago I got on the gas to go around an idiot that changed lanes right in front of me going half the speed limit/55. I ran it out for 10 seconds and when I slowed back down the motor stumbled for a 1/4 mile, then it went away. I have the pump and i'm going to put in today.
"Whining loud" could also be a plugged fuel filter. Have you tested fuel pressure? I'd have expected a failing pump to cause poor power, not stumbling after you've backed-off the throttle.
stutaeng
I'm Awesome
My brother once called me and asked if I could help him remove the bed of his c1500 to replace his fuel pump. Sure I said. So he shows up to my place and between Dad and the 2 of us we removed the bed...
I casually ask if he tested the fuel pump and he said no. So I asked how he knew it was bad? I pull out my DVOM and he had 12V and ground. We jumped the power wire and we could hear the pump working. I asked him if he had checked for spark and he said No. After a bit of BASIC diagnostics I concluded it was the pick up device on the distributor!
Anyway, it does sound like your pump "may" be the culprit, but it could also be other things. Basic checking costs nothing and only takes a few minutes.
In our case, a fuel pump would have cost him like $100, 3 hours of our time and would have fixed nothing! A new distributor was what fixed the problem. Don't be parts changer is all I'm saying...
Good luck
I casually ask if he tested the fuel pump and he said no. So I asked how he knew it was bad? I pull out my DVOM and he had 12V and ground. We jumped the power wire and we could hear the pump working. I asked him if he had checked for spark and he said No. After a bit of BASIC diagnostics I concluded it was the pick up device on the distributor!
Anyway, it does sound like your pump "may" be the culprit, but it could also be other things. Basic checking costs nothing and only takes a few minutes.
In our case, a fuel pump would have cost him like $100, 3 hours of our time and would have fixed nothing! A new distributor was what fixed the problem. Don't be parts changer is all I'm saying...
Good luck
HeavyAsAChevy
I'm Awesome
My fuel pump has been making a very loud whining noise. Does that point towards it starting to go out? It has been getting much louder recently.
HeavyAsAChevy
I'm Awesome
Ok. As for fuel filters, what brand do you like to use? I’ve just got a stock 4.3 if it makes a difference.
I use what ever the parts store has available. I think what is on my 95 with the gasser has a napa filter on it. I got a case of them from a previous job when we retired the last truck that used that filter. The truck will be dead before I use them all up lol.
454cid
Sooper Pooper
I like the bare stainless steel ones. Some of them are painted, and I doubt those are stainless. I really don't know what brands I've used. The one I just installed was stainless and looked good and installed it. It came from Gas Tank Renu with my nylon fuel line kit. I already had a Mahle on my parts shelf, but it's painted black. The black paint is why I used the bare stainless unbranded one, instead of the known brand. The Mahle wasn't painted in the Rockauto picture.
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