Fuel pressure test failure, where to start?

**LS1 oldtimer** · 03-23-2013, 04:09 PM

Takes several cranks to start the car so I did a fuel pressure test and this is what it does is:

Hooked the guage up without starting and there was no pressure. Turned the key on (without starting) and pressure built up to 59 then something clicks under the hood and the pressure falls immediately to near zero. While the car is running the pressure stays at 59, as soon as the key is turned off the pressure falls to zero. Another thing I noticed was when I unscrewed the gauge I could hear a little pressure escaping from the test port. Where should I start?

**pajeff02** · 03-23-2013, 05:20 PM

Not mess with the fuel system. Sounds like it is working fine to me.

**Knight** · 03-24-2013, 06:28 AM

Agree. With the description given, I don't see anything wrong.

**2002ssslp** · 03-24-2013, 10:07 AM

You may have some clogged injectors, plugs may need to be changed, How is your air filter, coils working ok. I would poke around and see what you can find. Pressure is fine.

**LS1 oldtimer** · 03-24-2013, 01:47 PM

Thanks for the replies. I thought it was supposed to hold the pressure. The air filter is new and the car runs perfect once it starts so I didn't think it would be the plugs.

**383ls6** · 03-24-2013, 03:17 PM

it should hold pressure for a couple of minutes. if it falls to zero immediately then you need to replace the fuel pump module.

**redbird555** · 03-24-2013, 03:35 PM

Originally Posted by 383ls6

it should hold pressure for a couple of minutes. if it falls to zero immediately then you need to replace the fuel pump module.

This^^^ You should see it hold pressure for a few minutes at least. Sounds like the pressure regulator has gone bad, so you you either need to disassemble the module and replace it or get a new module. Try this test to confirm, next time you start the car turn the key on and wait a few seconds then turn the key to start it. This will prime the pump first and I bet it will kick over.

***SMWS6TA*** · 03-25-2013, 09:18 AM

Most likely the drop in fuel pressure is a result of the pick up tube having a crack.

Does it do this at certin levels of fullness with the tank? Meaning does it do this when you're half full, 3/4, 1/4? That is another way to check.

**Knight** · 03-25-2013, 12:07 PM

Mine will drop pretty fast. I don't know if I'd call it immediate, but definately not a few minutes. Never had an issue.

OP- if you don't start the car, but turn the key on, and let the pressure build and fall, then turn the key off and back on again, does it build pressure again?

**pajeff02** · 03-25-2013, 01:34 PM

Same. If I turn on my ignition without starting the car, it will jump to 58 or 59 psi. After a few seconds, it'll drop into the 40's. Haven't really paid attention to what it does after that.

**LS1 oldtimer** · 03-25-2013, 05:09 PM

Turning the key and waiting a few seconds doesn't seem to help it but cycling the key on and off a couple times does seem to help.

**0rion** · 03-26-2013, 02:19 AM

sounds like a bad fuel pressure regulator to me.....it could possibly be as simple as the according hose in the tank that supplies the pump being cracked but normally that pressure wouldn't fall that fast I don't believe. I would open it up and inspect that hose first and then look at the regulator if that hose isn't cracked. GM parts direct lists a fuel pressure regulator ($3.20) but I'm not sure I've ever known anyone that's replaced just the regulator so I'm not sure how serviceable that part is. If you do find that it's the hose make sure you use submersible hose and not regular fuel line. You'll want to go to NAPA and ask for SAE 30R10 hose. Another good idea would be to replace your pump while you're in there with a racetronix pump since you'll be right there anyhow.