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Low fuel pressure? How do I check it?

Tiny
ROBERT LEE4
  • MEMBER
  • 2004 CHEVROLET TAHOE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 83,633 MILES
Fuel pump runs but has low pressure. Attempts to start but shuts off as soon as it fires. Will start and run with ether but shuts off as soon as throttle is pressed at all.
Monday, December 9th, 2019 AT 7:25 PM

33 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
What is the fuel pressure when you turn the key on without cranking the engine? Have you replaced the pump or made any repairs? Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Check out the diagrams (Below). Please let us know what happens.
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Monday, December 9th, 2019 AT 7:41 PM
Tiny
ROBERT LEE4
  • MEMBER
  • 8 POSTS
Pulled pump and sat it in a bowl of fuel and it sprayed like 3 feet. So I sprayed any dirt in it out and put it back in and it takes 3 cycles turning key off and on before fuel reaches the quick disconnect before rail and injectors. If it sits for even 5 minutes takes another 3 cycles off and on to get fuel to even drizzle out. Hooked everything up did a pressure test the needle moves maybe a cm. I was thinking pressure regulator but I can't find one anywhere to even try testing that.
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Monday, December 9th, 2019 AT 11:15 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Yep. Your pump is not supplying enough pressure. The regulator is part of the sender/pump and is not serviced separate.
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Tuesday, December 10th, 2019 AT 4:37 PM
Tiny
ROBERT LEE4
  • MEMBER
  • 8 POSTS
Yea I found a temporary solution, lol. I took a pump motor out of an older Tahoe and junked all but the pieces that hold the pump filter etc, and put the new pump into my casing and back into the tank and it runs good, but if I let off the throttle to suddenly after high speed it just shuts off, but starts immediately again.
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Tuesday, December 10th, 2019 AT 6:25 PM
Tiny
ROBERT LEE4
  • MEMBER
  • 8 POSTS
Also, I wasn't about to wrestle the tank out again. So my solution was a custom access straight to the pump through the floorboard.
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Tuesday, December 10th, 2019 AT 6:26 PM
Tiny
DBRUMMETT
  • MEMBER
  • 2 POSTS
  • 2003 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
Our 2003 Chevy Tahoe Flex Fuel system doesn't maintain pressure on the fuel line over time and has trouble starting. It rarely starts on first turn of key. We replaced the fuel pump, the fuel filter, the fuel regulator, the throttle body, the crank shaft positioning sensor and still had problems starting the truck. So we decided to check the fuel pressure. We found that after turning the key several times that our fuel pressure was normal and the truck would start but after sitting for an hour or more the pressure would leak down. When we put a gauge on it by the fuel filter the pressure stays consistent over time but when we put the gauge on the fuel rail it goes to zero over time. Is it supposed to do that? If not, what could be causing it? Remember we have already replaced the fuel pump and fuel regulator. The only thing we haven't replaced or checked is the fuel injectors.
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
At the fuel rail, does the pressure drop more than 5 psi in a minute? If so, after seeing everything you replaced, if it isn't an injector leak, I don't know what it is?
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
DBRUMMETT
  • MEMBER
  • 2 POSTS
Today we tested the pressure at the fuel rail and it is about 40 psi right after starting it and turning it off which we think is within normal limits for a Flex Fuel system. Then after a couple of minutes of turning it off the pressure went to 45 psi without us doing anything. It is holding steady pressure even after a couple of hours. But now has a new issue, when we start it, it starts running rough and dies. So it seems like the issue is intermittent. It is very frustrating because when it starts running rough it gives a code that there is a communication failure with the crankshaft positioning sensor which we have replaced twice. Also, there is a second code that says ATC failure. What is that about? We are beginning to wonder if this is a PCM problem. Any ideas?
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
It sounds like the fuel pump is bad.
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
GBARRAGAN1
  • MEMBER
  • 2 POSTS
  • 2003 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
What is the proper fuel pressure for a 2003 Tahoe
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
55-62 psi - Here is a guide to help you get the fuel pressure reading.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

Cheers
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
ANDREW42
  • MEMBER
  • 1 POST
  • 2002 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 130,000 MILES
I have a 2004 chevy tahoe I have changed the plugs factory new I have changed fuel pump twice I have changed all four o2 sensors and fuel filter and mass air flow sensor all new no used I have 42 for fuel pressure unless I accelerate past 3000 rpms then it drops very rapidly almost to 10 to 20 lbs if you just step into it it acts like it is running out of fuel driving me crazy I have gotten the to lean codes on bank I and two so thats what led to changing 02 sensors no improvement I am going insane it is the 5.3 e 85 flex fuel engine oh yeah also replaced fuel pressure regulator new as well please help thanks andy
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
BRIAN 1
  • MECHANIC
  • 1,030 POSTS
The fuel pressure should be between 48-54 psi, you either have a another bad fuel pump or a restriction in the fuel feed pipe. These are the only 2 things that can cause low fuel pressure. Is the fuel pump aftermarket?If it is I've never had good luck with aftermarket parts. Post back with any other questions.
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
SHAWN STANSBURY
  • MEMBER
  • 1 POST
  • 1999 CHEVROLET TAHOE
  • 220,000 MILES
Will run if poor fuel in by hand and will stay running if I keep spraying fuel by hand. Getting good pressure to the top on fuel bleed valve on top of the intake. Please help.
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

You need to test the actual pressure to be sure there is enough pressure. You can have fuel to the rail but not enough to have the engine run.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Can you hear the pump run when you turn on the key?

Key On Engine Off .................... 60-66 psi

Roy
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
Hello and thanks for stopping by. When you say "good pressure," have you actually measured the output with a pressure tester? Or did you just push on the valve and it sprayed out? If you just pushed the valve, then I suggest borrowing a fuel pressure tester from the local auto parts shop and running a pressure test. Pull the fuel pump relay and crank the engine a few times in order to relieve fuel pressure. Then hook up the pressure gauge. Put the relay back in. Turn the key on and see what it reads. These trucks require at least 60 psi to start. Any less will not do it.

If the pressure is just a few pounds short, try replacing your fuel filter. Instructions for that are in the images attached. If it's really low (like 30 psi or less) then you likely need a new pump, which is common to these trucks. In my experience, after 160,000 miles you're on borrowed time with these pumps.

Here's our official guide in checking fuel pressure. It's much better than AllData's guide. https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

So start there and left me know what you find. We'll go from there.

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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
Also, I'm assuming that you have the 5.7L gas engine and not the 6.5L diesel engine. Please let me know if I'm wrong.
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Wednesday, June 2nd, 2021 AT 2:44 PM (Merged)
Tiny
PHREDTOON
  • MEMBER
  • 3 POSTS
  • 1999 CHEVROLET TAHOE
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 223,000 MILES
I drove to my buddy's house and ran perfectly fine. I went to leave and it wouldn't start. It cranks over really well the battery is still strong. I thought it could be a clogged filter or the pump. I changed the filter and while the filter was disconnected I turned the key on and the pump made a big puddle of fuel. Could it still be the pump? I'm going back today to check for spark hopefully that pans out.
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Wednesday, June 2nd, 2021 AT 2:45 PM (Merged)
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Hi,

Yes, just because a pump is not able to start the vehicle does not mean it cannot pump any fuel. The best way to test a fuel pump is to measure your fuel pressure while cranking. Just because it can deliver some fuel does not mean it can deliver the proper amount of fuel.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know what you find and we can go from there. Thanks
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Wednesday, June 2nd, 2021 AT 2:45 PM (Merged)
Tiny
TODDONE14
  • MEMBER
  • 1 POST
  • 1997 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 17,500 MILES
Why do I have to spray my truck with ether to get it to start and then it shuts off when I put it into gear. And where is the fuel pressure regulator?
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Wednesday, June 2nd, 2021 AT 2:45 PM (Merged)

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