2005 escalade esv with 6.0 and only 30psi fuel pressure

[VikingTrad3r]

2005 escalade esv awd lq9 6.0



just bought it. exhaust smelled rich. both banks lean. diagnosis i discovered 34 psi fuel pressure at idle.



im fairly sure from my searching it should be +- 60psi.



from what ive read, there is NO fpr. or at least its built into the pump.



couple questions:



is there ANY thing other than a failing pump that this can be? massive vac leak? not sure if the fpr built into the pump is operated off vac?



how is it possible the truck starts and runs? it may be down on power but it feels similar to my 2006 lq4 denali xl.

 

[iamdub]

You trust that FP gauge? I didn't think these things would even run with pressure less than ~50.

The FPR is definitely not controlled by vacuum. If you have a return line from the intake manifold, the FPR is on the rail. For an '05, it should just have the supply line since (I believe) '04 was the year they went to a returnless fuel rail. I think the FPR is built into the pump module in the tank. For the Gen3 stuff, I'm more familiar with the Corvette and it's FPR is part of the filter assembly but I don't think that applies to trucks.

 

[VikingTrad3r]

i do trust the gauge. here is why:

this 05 esv escalade is replacing our 06 denali xl that was tboned but still runs and drives no problem.

i have the two trucks side by side. same engines other than domed pistons on the lq9.

denali is 56psi steady, no codes all is well. escalade as mentioned is 34. if i stan throttle on denali it holds its pressure. if i stab on esv it dips to 20psi. same gauge. so we can trust this gauge. i did have the exact same thought as u which is why i tested the denali.

i am not a hack, but i think i AM going to hack into the fuel pump in the denali from the floor boards using the hatch method and swap it into the esv. im constrained for time and the dealer wants 900$ for a pump that i can get off rockauto for 200.

plan is to swap pumps before wrecker comes to tow the denali away next wednesday.

 

[iamdub]

I'm surprised to hear that it'll run on such low psi. But, at least we know the gauge's readings are admissible which validates the low psi, and we already know that is definitely at least one problem if not THE problem.

I'd absolutely swap the pump as well as anything and everything else I wanted before the Denali gets towed! Having a known good pump in your yard and at your disposal is a huge convenience. I'd cut the floorboard in the wrecked one without hesitation- it's totaled and gonna be crushed anyway. While you're messing with the pump, check all the wiring, including the plugs and grounds. Make sure the connections are clean and tight. The low psi problem could be from the pump not getting full power due to a weak electric circuit. If you live in a rusty area, it could also be pinholes in rusted hard lines leaking fuel and, therefore, pressure. A failed O-ring in the fuel hose connectors is another possibility. The exhaust smelling rich doesn't coincide with a weak fuel supply and both banks reporting as lean. Is there a chance you have a small fuel leak and you were smelling the raw gas while you were back there sniffing the exhaust?

BTW, just for accuracy's sake, the pistons in the LQ9 are flat, not domed. They're dished in the LQ4, though. The LQ9 has a few upgraded build designs, too. Great motor!

 

[VikingTrad3r]

i would say zero chance of fuel leak. my nose is incredibly sensative lol.

POSSIBLE weak signal but highly unlikely given condition of vehicle. no rust. (why i bought it).

im starting to think clogged sock?

as for codes, my understanding is it works like this, pls correct if im mistaken.

exhaust reads lean, dumps fuel to bring 14.1-1 ratio back inline cause it cant reduce air, by keeping injectors open a tad longer than normal. is there a way to see on scanner if the injectors are staying open longer???

what’s interesting is that it is definitely overcompensating cause the exhaust is very rich smelling.

my wireless elm327 scanner is fubar, have a new one coming to view the fuel trims and o2 cycles.

I did clean the maf and put a bottle of seafoam in tank (i know...)

anyway as you say...34psi just isnt right...needs to be changed.

ps, appreciate the correction on the lq9 vs lq4 details. will have to find a list of differences somewhere.

 

[iamdub]

i would say zero chance of fuel leak. my nose is incredibly sensative lol.

POSSIBLE weak signal but highly unlikely given condition of vehicle. no rust. (why i bought it).

im starting to think clogged sock?

as for codes, my understanding is it works like this, pls correct if im mistaken.

exhaust reads lean, dumps fuel to bring 14.1-1 ratio back inline cause it cant reduce air, by keeping injectors open a tad longer than normal. is there a way to see on scanner if the injectors are staying open longer???

what’s interesting is that it is definitely overcompensating cause the exhaust is very rich smelling.

my wireless elm327 scanner is fubar, have a new one coming to view the fuel trims and o2 cycles.

I did clean the maf and put a bottle of seafoam in tank (i know...)

anyway as you say...34psi just isnt right...needs to be changed.

ps, appreciate the correction on the lq9 vs lq4 details. will have to find a list of differences somewhere.

I was thinking that if the fuel supply is weak, then how could the PCM make the exhaust rich even if it cranked up the injector duty cycle (IDC)? You can open your water spigot all the way, but if the water supply to your house is only a trickle... Ya know?

If the scanner can show live data, then it should be able to show the IDC (it'll be shown as a %)

But, you just made me think of something else. What if the PCM is erroneously being told that the exhaust is lean and it's maxing out the injectors in efforts to richen it up? The maxed out injectors would be like a leak and the pressure would drop. BUT, the pump should still be able to maintain the required ~50-something minimal psi even with the IDC at full capacity, so I still believe it has an issue. I'd pull the O2 sensors from the Denali as well. While you're looking at the IDC, check out the O2 sensor readings with the current ones and with the swapped ones from the Denali.

The key differences in the LQ9 are the flat-top pistons for increased CR and its stronger connecting rods. The rods are thicker with a bigger crank end and a bushed piston end for a full-floating piston pin. I believe they also had coated piston skirts. It may not be of much significance, but all LQ9s were built in Romulus, Michigan. IMO, keeping the build location exclusive would keep the build variances to a minimal.

 

[VikingTrad3r]

Yeah. Very likely more than one issue.

Can anybody verify that even with a huge vacuum leak the pump should be able to maintain 55+ psi on these returnless trucks?

Its possible i have a huge vac leak (need my scanner for fuel trims) and also have a weak pump.

it does seem very strange that a weak pump is capable of creating rich smelling exhaust.

that said, my tpi vette runs at 30 psi fine so id imagine the truck here could at least run.

 

[iamdub]

Engine vacuum has nothing to do with the designed rail pressure of the fuel system. A vacuum leak would mean more air going into the engine than what the MAF is seeing, so you'd have MAF code(s) and likely MAP code(s). You'd also have a high idle if the leak was big enough that the IAC couldn't compensate for it. Even if the IAC can compensate for the high idle, you may still get an IAC code if the PCM sees it having to operate beyond an expected range to achieve a specified idle speed.

The exhaust may actually NOT be lean. That's just what the PCM is seeing based on what it's being told by the O2 sensors. You determining the exhaust as being rich by it's smell is more factual. If it's been running rich for a while, the O2 sensors may be clogged with soot. This essentially plugs up the PCM's "nose" so it can't accurately sniff the richness of the exhaust and it thinks it's lean, so it ramps up the IDC to add more fuel to an already rich exhaust, which adds to the soot clogging up the O2 sensors. The catalytic converters would likely be getting clogged up as well.

I'd focus on and address the facts you've determined so far: Fuel pressure that's at least 20psi below minimum spec and a rich exhaust.

You have a known good fuel pump and various sensors and even a Y-pipe with presumably good cats to swap as needed at your disposal. I'd start with the fuel pump and O2 sensors, clear the codes and test.

 

[VikingTrad3r]

update: new pump installed. carter brand. 62 psi. having a very hard time getting the locking ring the full way into lock.


will be attempting to use an air hammer very gently to persuade that locking ring around.


i opted for the “hatch” door method.


It would have been much easier had i made a much larger hatch.


truck sounded very different idling. will clear codes and see what happens if the dual bank lean codes reoccur.

 

[iamdub]

I've fought aftermarket pump modules before and ended up either notching the plastic a hair to let the ring turn all the way or swapping the bulkheads with the factory one (if the rods line up) or swapping the new pump and strainer into the original module. I also test the level sensor since those fingers were known to make intermittent contact with the rheostat (?) and cause an erratic fuel gauge.