any gm technicians on here?

[Lone Wolf]

I am having trouble with 2 Chevy trucks 1997 and 1998 I believe it is fuel related and need assistance troubleshooting a bad fuel regulator from a bad fuel pump.

 

[Stihlbro]

What are the symptoms of the truck? Check engine light on?

 

[S Sidwell]

Checked fuel pressure at fuel filter connection?

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[S Sidwell]

My bad, forgot they had a test port, block off return and check pressure.

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[Lone Wolf]

What are the symptoms of the truck? Check engine light on?

RE 98 truck
sometimes it wont fire right away on first try but always starts, check engine light and a code for co sensors. Fuel pressure dont come up fast at all but goes to 50 and it holds when off. this is one truck we will stick with this a while first.Also when I rev it the vac has no effect on the fuel pressure gauge it stays steady and on all my other trucks it will jump. Also I cleaned MAF sensor and replace crank sensor and temp sensor and air and fuel filters. I have a fuel pressure regulator coming in the mail from Rock Auto tomorrow.

 

[Lone Wolf]

Here is the code

 

[Lone Wolf]

My bad, forgot they had a test port, block off return and check pressure.

Steve, Samsung On5 using Tapatalk

I put a vise grip in the return line and the pressure hit 80

 

[S Sidwell]

Have you tried to double cycle the key, and tried to start it on the second cycle?

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[S Sidwell]

Should be 60 psi to 65 psi when key switched on then drops to around 50 psi and hold when pump shuts off.

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[S Sidwell]

Yours sounds like my dad's 98 GMC, on second key cycle it will start, has a new fuel pump sitting in back seat, I haven't had time to replace it.

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[Stihlbro]

When you first key up, the fuel pump comes on and runs for a few seconds, then does not run until the cranking engine builds enough oil pressure to close the oil pressure switch.

I would install the pressure gauge, monitor fuel pressure not running, key on only, when cranking and while running. The spec is 60 to 65 psi but I've know several start/run with lower pressure. Make sure you are getting the prime stage(you should hear the pump run). Qualify the relay. You can swap it with another in fuse box. The thing about them spider pipes are the initial fuel pressure to start, once running it is not quite important. You can disconnect the vacuum line to the regulator while running and should see a increase in fuel pressure. If you snap the throttle the fuel pressure should increase then settle back.

As stated earlier, double cycling the key aids in the initial fuel pressure, the fuel pressure gauge should show if that is working.

 

[Lone Wolf]

When you first key up, the fuel pump comes on and runs for a few seconds, then does not run until the cranking engine builds enough oil pressure to close the oil pressure switch.

I would install the pressure gauge, monitor fuel pressure not running, key on only, when cranking and while running. The spec is 60 to 65 psi but I've know several start/run with lower pressure. Make sure you are getting the prime stage(you should hear the pump run). Qualify the relay. You can swap it with another in fuse box. The thing about them spider pipes are the initial fuel pressure to start, once running it is not quite important. You can disconnect the vacuum line to the regulator while running and should see a increase in fuel pressure. If you snap the throttle the fuel pressure should increase then settle back.

As stated earlier, double cycling the key aids in the initial fuel pressure, the fuel pressure gauge should show if that is working.

Why do you think I am not seeing the fuel pressure move when i hit the throttle? And I will be putting in a regulator in a day or two.

 

[S Sidwell]

Do the double key cycle and see if you get 60 to 65 psi.

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[S Sidwell]

If you don't achieve 60 to 65 psi on a double key cycle, block return line and see if you achieve 65 or better. If on second test you get over 65 on hold for two minutes without pressure loss, I'd say regulator. If it doesn't get up to 60 blocked, pump. If blocked and looses pressure, pump.

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[S Sidwell]

Some of us do this for a living, I work as a tech for a GM dealer, this is the type of tests you have to run to determine what's failing on the older systems, the newer systems, lost more test and headaces.

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[Lone Wolf]

Ok guys thanks I will report back tomorrow with more.

 

[Lone Wolf]

Some of us do this for a living, I work as a tech for a GM dealer, this is the type of tests you have to run to determine what's failing on the older systems, the newer systems, lost more test and headaces.

Steve, Samsung On5 using Tapatalk

Will blocking the return line damage a fuel regulator? I am wondering ? I read it in the book if it goes too high.

 

[S Sidwell]

You are just temporary blocking return line, not long term, you'll be ok.

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[woodtool89]

i had a 99 (old body style) that had the same problem and it would also starve for fuel when running down the highway every once in a while...new pump fixed it...ended up just cutting a hole on the bed and made an aluminum cover for it for easy access.

 

[S Sidwell]

We just raise the bed on the left side at home, drop the tank at work, lot easier with a lift and trans jack.

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