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2018 Tahoe 5.3 68k fuel pressure psi fluctuating

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2 years 2 weeks ago #63129 by Jowee
2018 Tahoe 5.3 68k fuel pressure psi fluctuating was created by Jowee
Can anyone tell me what’s wrong with my fuel pressure?  2018 5.3 65k with high and low fuel pressure pump.  I have rough idle and poor gas mileage. After I shut the engine off the pressure rises up to 80psi.  Thanks
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2 years 2 weeks ago #63136 by Bryan Pollock
Replied by Bryan Pollock on topic 2018 Tahoe 5.3 68k fuel pressure psi fluctuating
Ok, what codes and what cylinders is it misfiring on? What led you to look at fuel pressure? You can go down the wrong road when looking at the low side on one of these systems because sometimes fluctuations are normal. I work on tons of these and low side issues are rare

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2 years 2 weeks ago #63153 by Jowee
Replied by Jowee on topic 2018 Tahoe 5.3 68k fuel pressure psi fluctuating
No codes but I found intermittent random misfire on all cylinders .  I hookup a fuel pressure gauge to the fuel line and the needle is erratic bouncing around.  Same with my live data. 

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  • Tyler
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2 years 2 weeks ago #63154 by Tyler
Replied by Tyler on topic 2018 Tahoe 5.3 68k fuel pressure psi fluctuating
Large fluctuations in the low side can be common on GDI systems, as the low side is part of the return system for the high side. Unless you're seeing fuel pressure performance codes, I don't know that I'd sweat it.

For your rough idle, I'd be more interested in the specific misfire counts in Mode $06.

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2 years 2 weeks ago #63158 by juergen.scholl
Replied by juergen.scholl on topic 2018 Tahoe 5.3 68k fuel pressure psi fluctuating
Pressure in the hp rail going up after shutting down the engine is a normal condition. It happens because the fuel getting "heat choked" and the resulting thermal expansion.

Indeed this serves as test for leaks within the hp system: if the pressure does not rise an injector or the hp pump itself may be leaking.
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