WICobaltSS

Hey guys,
Finally got my cobalt running after a timing/balance shaft chain and tensioner replacement. I rented a fuel pressure tester from Auto Zone. After hooking it up and turning the key on/engine off, it read 15 psi. When I started it it read about 58 psi. I couldn't read it at various throttle positions as there was no one around to work the pedal.
What is the normal fuel pressure for key on/ engine off, idle, and WOT? Any of the numbers above seem out of range, and if so what could the possible causes be?
Thanks,
Jason

Slowbalt2000

iTrader: (1)

58 is what i should be but i might take a couple key cycles to reach that with the engine off

WICobaltSS

Thanks for the reply Slowbalt. I will wait a few days and check the pressure again with the engine off.
Thanks again!

Slowbalt2000

iTrader: (1)

Why wait?

WICobaltSS

Oh, I see what you mean, continuous key cycles will get the pressure up? I was thinking over a certain period of time. Sorry, I'm new at doing this...

ItalianJoe1

iTrader: (10)

If it comes up when running and doesnt' drop when you turn it off, it's ok.

When you shut the engine down it should maintain 50+psi for hours. If it drops right away you have a bad regulator.

WICobaltSS

I noticed when I shut the engine off that it did hold pressure. I guess my main concern was performing the key on engine off, the needle only went to 15 psi. I thought the pressure was supposed to go higher than that. What should the psi go to about say 3 or 4,000 rpm? (when the rev limiter is activated in park)
Thanks for all the help guys, I'm learning a lot as I go. Just glad to get the Cobalt back on the road!

Slowbalt2000

iTrader: (1)

The pressure should be pretty close to 58 during all running conditions. The only reason you cant get full pressure just by flicking the key to run is because the pump only primes for 2 seconds.

WICobaltSS

Ahh. Gotcha! I should be good to go. Thanks for the help.

WICobaltSS

OK guys, after experiencing longer crank time and rough idle on startup, which happens when the car sits overnight, I decided to do another fuel pressure test and the results were:
Key on engine off, 40 PSI
Idle and 2000 RPM, both 59 PSI
After shut off the pressure dropped to 45 PSI, 10 minutes later it dropped to 28 PSI, and another 10 minutes it dropped to 20 PSI.
I didn't notice any fuel leaks by the fuel tank nor the fuel rail. What could be the possibilities?
Thanks

exninja

iTrader: (1)

I didn't measure mine, but I just replaced the fuel pump on another car for this exact issue. It looks like the Cobalt is similar in that the check valve is integral with the fuel pump. If that's true, the solution would be to either install a separate check valve to the fuel line or get a new fuel pump.

exninja

iTrader: (1)

The check valve is there to keep pressure in the line. If the pressure drops that quickly and there are no leaks, then the check valve is bad. You can also combat this by allowing the fuel pump to prime before cranking the engine (free).

Edit: I just noticed there are more posts above your last one so imma go read them now. I'm on 4 hours of sleep so cut me slack.

I see the priming was already brought up. I mentioned it because it worked fine on my other car but it looks like you didn't have as much luck.

Slowbalt2000

iTrader: (1)

Its not gonna hold pressure forever. Your results are normal imo.

exninja

iTrader: (1)

I just looked at the specs for my Tiguan. It's a different car I realize, but the test for that one is:
1) build pressure to ~4 bar (58psi)
2) pressure must not drop more than 3 bar (43psi) after 10 minutes.
So your numbers would be ok according to that test.

WICobaltSS

Thanks for the response guys. I just cant figure out why the extended crank time (5-10 seconds) and a rough idle for maybe another 10-15 seconds? Another thing I was going to maybe try was pull the fuel rail and turn Key on engine off to see if there is an injector leak.

Slowbalt2000

iTrader: (1)

Are there any codes?

WICobaltSS

No codes. just those issues and lousy mileage 22 MPG mixed driving.

Slowbalt2000

iTrader: (1)

Changed air filter/ plugs recently? Miles?

exninja

iTrader: (1)

Check your fuel trim numbers as well

WICobaltSS

Plugs and filter are new (within a year for plugs, 2 months for filter) 123,000 miles on the odometer.
STFT was between -4 and +4 and LTFT was around -12.5.

exninja

iTrader: (1)

Someone can correct me if I'm wrong, but I would think a negative LTFT would mean you don't have a fuel delivery problem (or at least a fuel starvation problem)...

WICobaltSS

Possibly leaking injectors? Can a test for this be done with the fuel rail off and turning the key on engine off so the fuel lines pressurize?

WICobaltSS

FOUND THE PROBLEM!!! Got home from work tonight and I smelled a slight fuel odor. Popped the hood, nothing. Got behind and slid under the car and could smell gas. Then I noticed a wet spot near the front of the rear drivers side wheel. Rusted fuel line! The exact same location my daughter's Saturn leaked. Her's was a lot worse though.