: Fuel pump not priming



SDCaddyLacky
09-16-11, 10:31 AM
After replacing the fuel pump relay switch, I still don't hear the pump priming. I usually hear a slight humming sound when the key is turned to the "On" position, but not anymore.

Also when the car is running, I used to hear the fuel pump working, the sound was more prominent. Ever since the car ran out of gas, I don't hear the pump running anymore.

Does anyone know what else would cause the fuel pump to not prime besides for the fuel pump relay? I tested the connector to the relay, and there is power going to it. The fuses are good as well. BTW when testing the relay connector, what prongs are supposed to have current going to it? Only one prong had current flow when I tested it, while all the others didn't.

The car hasn't died on me or has stalled, and it runs ok, a slight funky idle here and there but other than that its smooth. Hard starting on cold starts is what i am dealing with at the moment.:nono:

Can a bad fuel pump-sending unit, cause the pump not to prime?

Thanks guys:cool2:

94 FWB

csbuckn
09-16-11, 11:15 AM
You can test for power at the pump, I think the wires are behind the bumper. Does it work if you put the old relay back it?

SDCaddyLacky
09-16-11, 12:36 PM
The old relay still works, I haven't tested for power at the connector near the bumper. I will for sure later when I get home. If their is power, my only other guess could be that the electrical connections inside the pump are bad. I hear that GM had a lot of problems with it electrical connectors for the fuel pumps.

if nothing else turns up, I will just replace the pump and sending unit to get done with. I have to replace the sending unit anyways, so I might as well do the pump while I am at it.

csbuckn
09-16-11, 09:19 PM
I think the pump is designed to be cooled by the gas so if you ran out of gas and it got louder, it probably wasnt gonna last much longer. Have you tapped the bottom of the tank to see if it turns on?

SDCaddyLacky
09-28-11, 12:15 PM
Update:

I finally decided to replace the sending unit and fuel pump. This cured everything. Gas gauge works again and the fuel pump primes. The strainer in the original pump was all black! It had a tear in it and it looked clogged.

I also saw that the float came off the little handle where it snaps onto the sending unit. One of the wires looked a little burnt at the connector too.

After I installed the pump, I notice that the engine idled smoother and the car gets up faster. Before while on the freeway it was hard to maintain or even get up to 70 MPH without having to mash the gas pedal, now the Caddy easily can go up to that speed and maintain it perfectly.

So if anyone has these problems with their Cads, please check the fuel pump, because it really did make a difference in curing the rough idle and fuel pressure problems.

If replacing the fuel pump relay doesn't fix your hard starting and (no prime condition), it's most likely the pump.

HUF
09-28-11, 10:51 PM
I do not believe one can hear PROPERLY running fuel pump while driving.

SDCaddyLacky
09-29-11, 12:38 PM
For some reason I would hear a humming sound coming from the back of the car at idle that was the pump. After awhile the noise went away. Now with the new pump it's completely quiet.

CAdiLLAK
11-20-11, 04:06 PM
For some reason I would hear a humming sound coming from the back of the car at idle that was the pump. After awhile the noise went away. Now with the new pump it's completely quiet.
i replaced my acouple months ago and also heard the humming noise while driving ,now couple days ago car didnt turn on an dont hear the pump run with key on like it should for two seconds....i dropped tank and am trying to figure out if its a circuit problem or pump went bad real quick....while iddling pump was really loud is that normal??

csbuckn
11-20-11, 07:20 PM
The only fuel pump I've heard while driving was one that went out in the next couple days. That thing would hum a new tone every time it started, then it went out. A good pump sounds strong and short when priming.

SDCaddyLacky
11-21-11, 11:00 AM
No that is not normal. I have had that humming sounding fuel pump for 2 straight years with no problems while driving, until it decided to act up recently, you can call that good luck I guess! You will always hear a slight hum, before the you start the car which is normal since that means the pump is priming, well I didn't hear that noise anymore, and that was when my starting problems came about.

Replacing the Fuel Pump, and Sending Unit fixed everything for me, I bought a whole unit with the pump and sending unit together including the strainer. What I realized while replacing the pump, is how much the strainer matters. I mean, it's really just a tiny filter, but over time dirt, moisture, and other junk can cause the strainer to get clogged, starving the pump of fuel, lowering the fuel pressure and fuel volume, which possibly can cause damage to the pump itself. Mine, was all black, and nasty looking. For sure the fuel pump in my 94 had to be the original pump, so I wasn't surprised by dirty strainer.

Did you replace the strainer when you replaced the pump? Or did the new pump already come with it? Because some replacements don't come with strainers.

Also it could of been that the new pump was a dud, take it back and get a new one, maybe even consider replacing the sending unit since it controls more than just the fuel gauge. Did you ever run out of gas since you replaced the pump?

CAdiLLAK
11-21-11, 01:46 PM
The only fuel pump I've heard while driving was one that went out in the next couple days. That thing would hum a new tone every time it started, then it went out. A good pump sounds strong and short when priming.
so its not suppose to hum while driving only to prime before starting....what would cause it to hum constantly ,a defective pump ??


No that is not normal. I have had that humming sounding fuel pump for 2 straight years with no problems while driving, until it decided to act up recently, you can call that good luck I guess! You will always hear a slight hum, before the you start the car which is normal since that means the pump is priming, well I didn't hear that noise anymore, and that was when my starting problems came about.

Replacing the Fuel Pump, and Sending Unit fixed everything for me, I bought a whole unit with the pump and sending unit together including the strainer. What I realized while replacing the pump, is how much the strainer matters. I mean, it's really just a tiny filter, but over time dirt, moisture, and other junk can cause the strainer to get clogged, starving the pump of fuel, lowering the fuel pressure and fuel volume, which possibly can cause damage to the pump itself. Mine, was all black, and nasty looking. For sure the fuel pump in my 94 had to be the original pump, so I wasn't surprised by dirty strainer.

Did you replace the strainer when you replaced the pump? Or did the new pump already come with it? Because some replacements don't come with strainers.

Also it could of been that the new pump was a dud, take it back and get a new one, maybe even consider replacing the sending unit since it controls more than just the fuel gauge. Did you ever run out of gas since you replaced the pump?
i replaced the fuel pump and strainer together they were sold separetly....im also messing around with wiring gonna have a buddy hopefully come and help me check it out today but im considering getting pump replaced under warranty and getting the sending unit as well, i havent ran out of fuel

SDCaddyLacky
11-21-11, 10:31 PM
Definitely replace the sending unit since the tank will be dropped, the wiring burns up over time or just simply fails. If you do all that, and your still having problems, make sure your fuel lines are not clogged, also check the fuel pressure regulator, and all electrical connections that have to do with the fuel system.

csbuckn
11-21-11, 11:43 PM
I dont think a good pump should run louder than engine noise. What car do you have?

CAdiLLAK
11-22-11, 03:51 PM
Definitely replace the sending unit since the tank will be dropped, the wiring burns up over time or just simply fails. If you do all that, and your still having problems, make sure your fuel lines are not clogged, also check the fuel pressure regulator, and all electrical connections that have to do with the fuel system.
i replaced pump and fixed the problem and new one is not loud

SDCaddyLacky
11-22-11, 07:42 PM
There you go! It was a faulty pump after all.