05 Tahoe Z71 Fuel Pressure Question

3joh · May 27, 2024

05 Tahoe Z71 non Flex
New long block with approx 5K on the clock.

occasional symptoms:
hard start
rough idle
lack of power

intermittent knock sensor code, random misfire code.

Injectors have been replaced, throttle body cleaned, new wires, plugs, coils when engine was replaced.

The tahoe has 280k on the clock but in Florida looks like new with original paint and rust free chassis.

Original fuel pump
Fuel pressure measurements:

with engine running 60 psi and does not drop while increasing rpm's in neutral
with key on (engine not running) gauge reads 49 psi and within 1 minute is below 30. rapid drop

I am thinking original fuel pump needs replaced. Cannot see any external leaking on injectors. Injectors were replaced at 272 k miles with GM replacements.

Thoughts?

Fless · May 27, 2024

Looks like your KOEO pressure should be 55 to 62 psi. Fuel Pressure specs, 1999-2006 Haynes:

3joh · May 27, 2024

Fless said:
Looks like your KOEO pressure should be 55 to 62 psi. Fuel Pressure specs, 1999-2006 Haynes:

View attachment 429291

thanks for this info. probably time to change the fuel pump.

Fless · May 27, 2024

Your regulated operating pressure might be high -- these tend to run more in the mid-40psi range -- and you may want to look into a quality replacement fuel pressure regulator and re-check.

Hard starts can also be caused by a leaky injector, but hopefully the ones you bought are balanced and aren't acting up. Also a purge valve staying open (or being intermittent) can flood the cylinders while it's not running. Have you tried clear flood mode when experiencing a hard start?

3joh · May 27, 2024

Fless said:
Your regulated operating pressure might be high -- these tend to run more in the mid-40psi range -- and you may want to look into a quality replacement fuel pressure regulator and re-check.

Hard starts can also be caused by a leaky injector, but hopefully the ones you bought are balanced and aren't acting up. Also a purge valve staying open (or being intermittent) can flood the cylinders while it's not running. Have you tried clear flood mode when experiencing a hard start?

during a hard start if i turn the key off and back on it will start immediately. The regulator is on the pump if I am not mistaken. I looked on the fuel rail on the driver's side and did not see anything there.

3joh · May 27, 2024

3joh said:
during a hard start if i turn the key off and back on it will start immediately. The regulator is on the pump if I am not mistaken. I looked on the fuel rail on the driver's side and did not see anything there.

also after the hard start there isn't any smoke or fuel smell from the exhaust.

Fless · May 27, 2024

I'd be surprised if your fuel rail didn't have one. Got a pic of yours?

3joh · May 27, 2024

Fless said:
I'd be surprised if your fuel rail didn't have one. Got a pic of yours?

View attachment 429320

Fless · May 27, 2024

Ha! Yes, I'm surprised.

Meathead16 · Jun 3, 2024

My 05 Avalanche had a returnless style fuel system. Instead of using a pressure regulator, the pump itself would be controlled by the PCM to regulate how much fuel was sent to the rail depending on fuel demand. It was a flex fuel but I'm pretty sure it's the same concept for all returnless systems.

Check over the wiring and such to ensure it's not a communication issue between the PCM and the fuel pump and if all checks out, most likely time for a new pump. 280k on the original pump is impressively uncommon!

05 Tahoe Z71 Fuel Pressure Question

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