Fuel Pressure PSI

diezelraccoon · Aug 31, 2024

I have an 03 Tahoe with the 5.3. I posted another thread about how when it gets to 1/4 tank or lower after sitting several hours it sometimes takes a couple extras cranks before it fires up. Someone had mentioned to check the fuel pressure. The readings are as follows.

46 psi when key was on but engine off.
42 psi with engine running
42 psi after engine was off

My question is are these normal ratings? If not, does that mean the fuel pump is getting weak and could be what is causing my issue and needs to be replaced?

strutaeng · Aug 31, 2024

Is this an LM7 or L59 engine? The L59 had lower pressure than the LM7.

afpj · Aug 31, 2024

Flex fuel key on, engine off, 48-52 psi. Non flex higher, so either way, you could be heading towards a new fuel pump.

Fless · Aug 31, 2024

According to Haynes:

KOEO
Flex Fuel: 48-54 psi
Non-Flex: 55-62 psi

diezelraccoon · Sep 1, 2024

strutaeng said:
Is this an LM7 or L59 engine? The L59 had lower pressure than the LM7.

The 8th digit in my VIN is a 7 so it’s the LM7

strutaeng · Sep 1, 2024

diezelraccoon said:
The 8th digit in my VIN is a 7 so it’s the LM7

Oh, definitely low then, based on @Fless post above...

You can temporarily disconnect the return fuel hose and cap the line, then prime the system to see what the most static pressure head the pump can deliver.

rockola1971 · Sep 1, 2024

Sure looks like the fuel pump is done. They typically drag the death process out forever and just get worse and worse and cause all kinds of problems like rough running, hard to start, running lean, stalling and on and on. They ALWAYS wait until you completely fill the tank and are out in the middle of nowhere to finally die. They are evil! The devil's spawn!!!!

diezelraccoon · Sep 1, 2024

strutaeng said:
Oh, definitely low then, based on @Fless post above...

You can temporarily disconnect the return fuel hose and cap the line, then prime the system to see what the most static pressure head the pump can deliver.

So I’m a bit confused. I opened the fuel door and there is this sticker. Is that just some standard sticker they put in all of them flex fuel or not?

strutaeng · Sep 1, 2024

diezelraccoon said:
So I’m a bit confused. I opened the fuel door and there is this sticker. Is that just some standard sticker they put in all of them flex fuel or not?View attachment 436811

Interesting. Yeah, that seems like flex fuel label. Are you the original owner of this truck?

Can you post a photo of the injectors? The L59 are visually different than those from the non flex-fuel variants.

Things get swapped over the years and ownership. Possibly engine, glovebox or fuel door are not original?

For example:
On my 99 Silverado I swapped the engine from a V6 to an L59, transmission from a 4L60e to a 4L80e, and last year I deleted to center console to a jumpseat (including the glovebox with another truck's RPO code label.) I did keep my old glovebox, and I was going to swap the lid, but even then, stuff doesn't match exactly. LoL

Fless · Sep 1, 2024

diezelraccoon said:
The 8th digit in my VIN is a 7 so it’s the LM7

I think the 8th digit is an alpha character, not a number. Would you take another look at your VIN? Bet it's a "Z."

Fuel Pressure PSI

diezelraccoon

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strutaeng

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afpj

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Fless

diezelraccoon

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strutaeng

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rockola1971

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diezelraccoon

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strutaeng

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Fless

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