2013 normal operating fuel pressure?

[lt1gmc]

My 2013 Denali recently dropped mileage a decent amount and developed a slightly rough idle. Have run 2 tanks of fuel injector cleaner, check for leaking injector (no pressure loss on sitting off for 10 minutes), and no misfire codes. Checking fuel pressure found static and startup 60 psi, then a few minutes later it drops to 43 psi at idle, which is the exact same time the idle begins to become slightly rougher. You can tell when the fuel pressure drops by the change in idle quality.
My older 09 Yukon operated at 59 psi steady all the time. Both vehicles have the FSCM instead of regulator so not sure if that is the problem or not. No codes, and LT and ST values in range of +3 to +5%.
Any ideas of normal operating pressure?

 

[OR VietVet]

Key on engine off should be between 55 to 65 psi, if I remember correctly. it is also not abnormal for it to bleed off just a bit while sitting there. 43 psi is not good because at idle the fuel pressure should be between the range of no lower than 52 to 53 and as high as 58 to 59 or so. Sounds like it is time for an AC Delco fuel pump replacement and I always recommend a new fuel filter at the same time. I have even went so far as to replace the relay as well.

 

[Joseph Garcia]

I cannot help you with this specific issue, but I'm sure that folks in the know will chime in.

 

[kbuskill]

If your truck is a Flex Fuel then 43 psi is normal while running.

 

[OR VietVet]

If your truck is a Flex Fuel then 43 psi is normal while running.

That is good to know but why would it be less? Not doubting, just curious.

 

[kbuskill]

That is good to know but why would it be less? Not doubting, just curious.

I have no idea... James @swathdiver may be able to tell us more... he has the factory service manual.

I should clarify that the 43 psi is for the Flex fuel 5.3l... I assumed it would be the same for the 6.2l in the Denali.

 

[swathdiver]

My 2013 Denali recently dropped mileage a decent amount and developed a slightly rough idle. Have run 2 tanks of fuel injector cleaner, check for leaking injector (no pressure loss on sitting off for 10 minutes), and no misfire codes. Checking fuel pressure found static and startup 60 psi, then a few minutes later it drops to 43 psi at idle, which is the exact same time the idle begins to become slightly rougher. You can tell when the fuel pressure drops by the change in idle quality.
My older 09 Yukon operated at 59 psi steady all the time. Both vehicles have the FSCM instead of regulator so not sure if that is the problem or not. No codes, and LT and ST values in range of +3 to +5%.
Any ideas of normal operating pressure?

Steve, does the 43 psi actual pressure match the commanded pressure? 43 psi (43.5) is normal for a FlexFuel engine. If the pump or something is amiss, it might not have enough volume at that pressure.

Can you run an injector balance test with your scan tool?

Once warmed up, how do the downstream O2 sensors look? Fairly steady or moving around like the upstream sensors? It's been my experience that a loss of gas mileage while everything is fine has been a precursor for new cats. Not always but often enough.

 

[OR VietVet]

O2 sensors reveal so much helpful info. I started with points and condensor vehicles. Then came the first computer and then fuel injection. I was dreading it all and the learning curve but then I saw the real advantage of fuel injection over those garbage computer controlled carbs. What an eye opener, even back then. Better and better as years passed.

 

[lt1gmc]

Mine is not flex fuel. Not thinking the pump is bad because at full throttle revs to redline so has enough fuel, but after starting, fuel pressure is at 60, but drops quickly to 43 or so in a minute or two. At the same time the idle becomes rougher by a little bit but noticable. Trying to figure out if the FSCM is supposed to keep a pretty much consistent pressure thruout the range or vary that much. My 09 was consistent 58-60 on fuel pressure.
Did reseat the electrical connector on the FSCM, and noticed the FSCM bolts had the appearance of having been removed previously. Only had the Yukon for 3 months, at 90k miles.

 

[Doubeleive]

my 2012 6.2l has 65 pre-start, and then 45 running psi I personally feel it is little on the low end I would rather it have at least 50psi running but I don't have any problems with it.
this is via a fuel pressure gauge