Where do i start

jlahood

Member
My son's 2000 Sonoma just quit running while he was driving down the road. I noticed in the past his fuel pump was pretty loud. I suspect it is gone. Is there a for sure way to check and see if it is bad?
 

Wooluf1952

Well-Known Member
First check the fuse.
If that's good, you should hear it run when you turn the key to the RUN position.
If both those are good and it still wont run, got a fuel pressure tester.
I'm not sure what the pressure should be.
 
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jlahood

Member
I can hear it run when I turn the key on but it sounds like it is not running steady. Like it is cutting out or weak.
 

JerryIrons

Well-Known Member
Sometimes you can turn the key to run, without starting, and listen for the fuel pump to run a few seconds to pressurize up. Then, don't try and start it, but turn key off, and then just to run, repeating what you just did. Eventually, you should reach a point where the pump doesn't run, because the pressure is up to par. Then, try and start your car. I'm assuming the engine actually turns over?
 

northcreek

Well-Known Member
As already stated, a pressure test would be the best indicator. There is a fitting on the fuel line/manifold at the engine,it is an A/C type fitting so an A/C gauge would work. Gm often leaves a wire exposed in the harness near the battery (on my Pontiac it was orange) it is there so that you can jumper it directly to the battery to allow the pump to run for test purposes.
A less sophisticated test would be to depress that fitting to see if you get pressure, perhaps into a clear plastic bag for safety...Mike.
 

christo829

Well-Known Member
If you've got an Auto Zone or Advanced Auto Parts nearby, they may have a fuel pressure gauge
you can rent if you don't want to just buy one outright.

Not sure about the Sonoma, but our Trailblazers want around 55-60 psi.

If you've just run the pump up to pressure like JerryIrons says, watch out for a spurt of
pressurized fuel when you hook up the gauge.

The "squirt it in a bag" check that Northcreek mentions will show you it has pressure, but not
if it's sufficient. My old Lumina needed about 50 psi, and it would give that when it first started up,
but after a few minutes of running it would drop to 24. That was sufficient to keep it going, but at a stop
light or low speed, it would die if I hit the gas.

Good Luck!

Chris
 

AbsoluteZero

Well-Known Member
The fuel pump on my 95 is noisy so I wouldn't assume it's the culprit without checking other failure modes such as spark. The advice on checking pressure is good. Typically a fuel pump with run for 2 secs when the ignition is first cycled on. This is to prime/pressurize the fuel line. I can't comment on an 02 but on my 95 there's what called a fuel pump prime lead along the driver's side fender near the brake booster. When connected to 12v it will run the fuel pump, If you have a volt meter or test lamp I recall 12v will be present on this lead for the 2 sec when you first turn on the key and if the engine is running it will also have 12v present. If the 02 has the prime lead you can power the fuel pump without the 2 sec delay. On my 95 fuel pump power is supplied thru contacts in the oil pressure switch... if there's a roll-over and oil pressure drops to zero the fuel pump won't run. In any case you need to confirm the fuel pressure and go from there. Wiring diagrams may be available thru AutoZone or your public library. Many have Mitchell's online.
 
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jlahood

Member
So I disconnected the fuel filter and turned the key on. Fuel pumped out through the filter. I hooked it back up and ran the pump a few times to prime it. I then pushed a small screwdriver in the schrader valve and there is no pressure at all.
 

northcreek

Well-Known Member
jlahood said:
So I disconnected the fuel filter and turned the key on. Fuel pumped out through the filter. I hooked it back up and ran the pump a few times to prime it. I then pushed a small screwdriver in the schrader valve and there is no pressure at all.
You could have a bad pressure regulator, it could be stuck/failed open and just pumping back into the tank via the return line...Mike.
 
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jlahood

Member
northcreek said:
You could have a bad pressure regulator, it could be stuck/failed open and just pumping back into the tank via the return line...Mike.
Is there a way to test it.
 
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jlahood

Member
So I bought a fuel pressure test gauge today. I did have fuel pressure at the schrader valve. But the gauge only went to 15 psi when I cycled on the pump. I guess that would suggest the fuel pump is too weak to pump sufficiently? I also noticed when I turn the key on the pump cycles on for about 2 seconds and when I turn the key off it cycles again for about two seconds. Is that normal? Where is the pressure regulator located at? I read something about it being under the intake plenum.
Thank you all for your help.
 

AbsoluteZero

Well-Known Member
jlahood said:
So I bought a fuel pressure test gauge today. I did have fuel pressure at the schrader valve. But the gauge only went to 15 psi when I cycled on the pump. I guess that would suggest the fuel pump is too weak to pump sufficiently? I also noticed when I turn the key on the pump cycles on for about 2 seconds and when I turn the key off it cycles again for about two seconds. Is that normal? Where is the pressure regulator located at? I read something about it being under the intake plenum.
Thank you all for your help.
Normal to recycle on for 2 sec when the ignition is recycled.
If there's a hose connection in the return line from the pressure regulator you can try pinching closed. Probably located under the truck.... If pressure builds up that's an indicator of a leaking pressure regulator. If not I'd suspect either a bad fuel pump or the short hose connection between the pump and fuel line in the tank has developed a leak. If the hose connection is leaking be sure to replace with hose rated for submersion in fuel. Regular fuel line hose isn't.
Don't know where the pressure regulator is located on a 2000 model but you are probably right. You might check to see if available as a separate unit so you don't have to buy the entire injector assembly.
 

Wooluf1952

Well-Known Member
Sorry. I was looking at your truck info.
 

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