Fuel pump prime slow?
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Joined: May 2005
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Fuel pump prime slow? Just wondering if anyone else notices their fuel pump sounding like it's priming slowly (the hum sound when you turn the key but before cranking the engine) if the car has been sitting for a while (LT1 engine).
The car starts right up and runs awesome with no SES light, but I'm wondering if the slow prime is normal for a car that sits for several days at a time, or if it's a sign that something's about to go wrong. Thanks!
The car starts right up and runs awesome with no SES light, but I'm wondering if the slow prime is normal for a car that sits for several days at a time, or if it's a sign that something's about to go wrong. Thanks!
Just to clarify.
Does the pump sound like it is actually running more slowly, or does it run for an extended period of time before you hear it start making pressure?
If it is running slowly, maybe the battery voltage is a bit low or the pump is getting weak.
It is normal for the fuel pressure to bleed off over time which is why the priming cycle is needed to rebuild pressure, especially if you don't use the car for a few days.
Most race pumps lack the internal one way check valve altogether, and will require an increase in the pump prime cycle to be programmed in the pcm for proper startup.
Does the pump sound like it is actually running more slowly, or does it run for an extended period of time before you hear it start making pressure?
If it is running slowly, maybe the battery voltage is a bit low or the pump is getting weak.
It is normal for the fuel pressure to bleed off over time which is why the priming cycle is needed to rebuild pressure, especially if you don't use the car for a few days.
Most race pumps lack the internal one way check valve altogether, and will require an increase in the pump prime cycle to be programmed in the pcm for proper startup.
Thread Starter
TECH Regular
Joined: May 2005
Posts: 470
Likes: 4
It is normal for the fuel pressure to bleed off over time which is why the priming cycle is needed to rebuild pressure, especially if you don't use the car for a few days.
Most race pumps lack the internal one way check valve altogether, and will require an increase in the pump prime cycle to be programmed in the pcm for proper startup.
Most race pumps lack the internal one way check valve altogether, and will require an increase in the pump prime cycle to be programmed in the pcm for proper startup.
Thread Starter
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Joined: May 2005
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Well, I still seem to have a slow fuel pump prime on a cold engine.
Today, I noticed if I turn the key once to "prime" the engine, and it is slow, I turn the key off and don't hear the "whistle" sound I normally hear when I turn the ignition off (while the engine is NOT running). I then proceed to turn the key to the ON position and heard a strange "mechanical sound" under the hood!
(sounded like it came from the passenger side under the hood). Any ideas what that could've been? Thanks!
BTW, car started right up after that...and continues to run like a champ...
Today, I noticed if I turn the key once to "prime" the engine, and it is slow, I turn the key off and don't hear the "whistle" sound I normally hear when I turn the ignition off (while the engine is NOT running). I then proceed to turn the key to the ON position and heard a strange "mechanical sound" under the hood!
(sounded like it came from the passenger side under the hood). Any ideas what that could've been? Thanks!BTW, car started right up after that...and continues to run like a champ...
Thread Starter
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Joined: May 2005
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Took my car in for service, and mentioned to the dealer that the fuel pump prime sounded slower when cold vs warm. They test fuel pressure and the readout was 45PSI engine off, 35PSI when on. So, they tell me the fuel pump is going bad and needs to be replaced. So naturally I asked them to do it.
I must admit that the car definitely feels a bit stronger after replacing the pump and the fuel injection cleaning (PSI is not 58, and according to GM is in spec). However, the fuel gauge is not reading accurately (I thought the gas was a little low from when they were replacing the pump, but when I filled it up the gauge went between 3/4 and F (where it used to be about 3-4MM beyond the F when full).
So I brought it back to them and am hoping they will fix this since I just parted with a whole lotta $$$ to have this pump replaced. They tell me "well, we cannot prove what the previous readout was on the fuel gauge". They also say I may need to wait for another fuel pump to arrive. I also asked if they can just use the sending unit from my old pump since it always worked with no issue.
Any imput on how I should continue to proceed?
I must admit that the car definitely feels a bit stronger after replacing the pump and the fuel injection cleaning (PSI is not 58, and according to GM is in spec). However, the fuel gauge is not reading accurately (I thought the gas was a little low from when they were replacing the pump, but when I filled it up the gauge went between 3/4 and F (where it used to be about 3-4MM beyond the F when full).
So I brought it back to them and am hoping they will fix this since I just parted with a whole lotta $$$ to have this pump replaced. They tell me "well, we cannot prove what the previous readout was on the fuel gauge". They also say I may need to wait for another fuel pump to arrive. I also asked if they can just use the sending unit from my old pump since it always worked with no issue.
Any imput on how I should continue to proceed?
