Incorrect fuel pressure Key on and Engine Running

[Matthew Jeschke]

I'm moving this from another thread. My fuel mileage has been suffering for quite some time and I think this is contributing factor. I honestly, only really know basics of troubleshooting fuel pressure. Maybe this is operating correctly, or maybe not?

Vacuum Check: I did a sanity check, revved the engine and fuel remained low by 20%. So I suspect it's fuel.

Rail Pressure:

Key on Ignition off: 50 PSI (I think should be ~58PSI ?)
Engine Running: 50 PSI when revved the pressure drops quickly down to nearly ~45 PSI
Pressure bleads off slowly when ignition is shut off. I'm not sure if it should hold 50PSI in there? It slowly bleeds down but engine starts like a champ... check ball bad in pump?

FEW NOTES/ BACKSTORY: Truck is a custom built LQ9 w/ Flex Fuel injectors. Note I went from around 24lbs / hr to ~32 lbs per hour... although, I don't think I had the fuel demand so flow should be similar to stock injectors maybe if anything a touch higher? I swapped the Flex Fuel injectors in because my 24# stock LQ9 injectors were leaking. Long story short, I think fuel demand / load on pump is VERY similar to the stock injectors (if anything I shortened the injector duty cycle). I tuned the VE table and am running in speed density mode. I went to log some more data a couple months later and noticed instead of my LTFT being well within 5% as tuned they are now around 20%.

New OEM pump - as spec'ed for LQ9 (not flex fuel, swapping whole system to flex fuel was a LOT of work / didn't have all the parts).
New pressure regulator on order - note when I unplugged the regulator w/ engine running pressure shot to 58 PSI.
Got a new filter to install

VIDEO OF SYMPTOMS LINKED HERE

UPDATE: I attached a copy of the spec for the pump I installed.

 

[Scottydoggs]

seems pretty normal to me. maybe the o2's are high miles and wearing out but not yet setting a code. as the o2's do have a say in fueling.

 

[strutaeng]

Are there any variations between the left and the right banks? Or pretty much identical?

I don't know the fuel pressure specs off the top of my head...

 

[Matthew Jeschke]

@Scottydoggs thanks for tip... The O2's are new also confirmed readings with Wideband. PCM is correctly reading AFR and trims are adjusting fuel as expected. If I reset the trims the engine will stumble and misfire. Just I don't know where the 20% trim / fuel error is coming from. If it was indeed tuning issue I'd be at 60 VE at idle which seems somewhat high (100 is perfect efficiency / pumping).

Running through FSM the Key on Ignition off pressure is wrong. It supposed to be between 55 and 62 PSI. I noticed it will go to that if I (1) start the engine and (2) disconnect the vacuum line from the regulator. But engine has to be running. I don't know if this points to the regulator... The FSM only specs pressure with engine off for that test... and unfortunately, I don't have a fitting to do it as FSM says.

@strutaeng I need to double check that. There's a PID in HP tuners that lets me see how far apart they are. They do vary some but I cannot say to what degree. You mentioned in other post but if they vary would you say exhaust leak?

...

I've been fiddling with the fuel pressure gauge and walking through factory service manual. It leads me to...

1. Bad fuel pressure regulator
OR 2. do a visual inspection of components between the regulator and the pump.

The method to check regulator is to test pressure between regulator and return to tank, should be greater than 62 PSI but lower than 75 PSI. Unfortunately, I don't have fittings to test the return line.

I did a visual inspection of regulator to front of tank and all appears good. I dropped the tank a few months ago to rebuild the evap and lines were good then. I felt up by the pump with my hand and it wasn't wet / leaking.

UPDATE: Engine oil looks good, it doesn't appear to be washed out from any gasoline and I'm near the oil change interval.

 

[strutaeng]

@Scottydoggs thanks for tip... The O2's are new also confirmed readings with Wideband. PCM is correctly reading AFR and trims are adjusting fuel as expected. If I reset the trims the engine will stumble and misfire. Just I don't know where the 20% trim / fuel error is coming from. If it was indeed tuning issue I'd be at 60 VE at idle which seems somewhat high (100 is perfect efficiency / pumping).

Running through FSM the Key on Ignition off pressure is wrong. It supposed to be between 55 and 62 PSI. I noticed it will go to that if I (1) start the engine and (2) disconnect the vacuum line from the regulator. But engine has to be running. I don't know if this points to the regulator... The FSM only specs pressure with engine off for that test... and unfortunately, I don't have a fitting to do it as FSM says.

@strutaeng I need to double check that. There's a PID in HP tuners that lets me see how far apart they are. They do vary some but I cannot say to what degree. You mentioned in other post but if they vary would you say exhaust leak?

...

I've been fiddling with the fuel pressure gauge and walking through factory service manual. It leads me to...

1. Bad fuel pressure regulator
OR 2. do a visual inspection of components between the regulator and the pump.

The method to check regulator is to test pressure between regulator and return to tank, should be greater than 62 PSI but lower than 75 PSI. Unfortunately, I don't have fittings to test the return line.

I did a visual inspection of regulator to front of tank and all appears good. I dropped the tank a few months ago to rebuild the evap and lines were good then. I felt up by the pump with my hand and it wasn't wet / leaking.

UPDATE: Engine oil looks good, it doesn't appear to be washed out from any gasoline and I'm near the oil change interval.

Exhaust leak? I think technically yes, but that would have to be HUGE exhaust leak and between the manifolds and upstream O2. Probably not likely to be culprit.

You can try plugging the return line at the fuel rail (disconnect the hose). Vacuum caps with fuel hose clamps will work. Then prime the system to see how much pressure (or head pressure) the pump is capable of providing. Should be like 80 psi IIRC. This test rules out the pump as being the problem.

 

[Matthew Jeschke]

I will see if there's another fitting for return line. I was trying to use the T adapter. I probably pictured doing it wrong.

I noticed I occasionally get a P0141 O2 Heater Circuit (Bank 1, Sensor 2)... I only replaced the front O2 sensors (ones closest engine).

I revved engine from 600 to 3000 RPM again and watched... The problem does slightly improve

At 2000+ RPM the O2 sensors start to separate... Bank 1 is 2 to 3% richer on up to 3200 RPM

Thanks for tips! I need to get this fixed ASAP as I need to drive it for work.

 

[strutaeng]

I will see if there's another fitting for return line. I was trying to use the T adapter. I probably pictured doing it wrong.

I noticed I occasionally get a P0141 O2 Heater Circuit (Bank 1, Sensor 2)... I only replaced the front O2 sensors (ones closest engine).

I revved engine from 600 to 3000 RPM again and watched... The problem does slightly improve

At 2000+ RPM the O2 sensors start to separate... Bank 1 is 2 to 3% richer on up to 3200 RPM

Thanks for tips! I need to get this fixed ASAP as I need to drive it for work.

View attachment 430923

View attachment 430922

The O2 codes are usually the "effect" of engine running lean. If you fix the lean condition, those usually go away.


Why do you have a misfire code? That would most definitely cause lean running conditions.

 

[Matthew Jeschke]

I thought I maybe aggravated the code by troubleshooting this. It seemed to come up when I started it and it was running really lean.

I will pull some spark plugs and see how they look. hrm...

 

[Fless]

If I read that right your graphic is LT trims -- you should watch short terms trims because they're essentially real time.

 

[Matthew Jeschke]

Yes, I'm watching both short term and long term. There's a split of 3% over 1500 RPM. Bank 2 is running 3% leaner than Bank 1.

Oh God, I went to put in the new fuel filter. What a nightmare. I'm in quite a bit of pain. I depressurized the system. Then disconnected the line set going through the filter along with mounting bracket... It started siphoning fuel out of the tank. Fuel was going everywhere. I tried like hell to swap the new on in quick but I kept getting soaked in gas. I'd have to run spray myself with a garden hose and work some more. It was almost impossible to line up the lines with the new filter while being showered in gas. I finally got it but not before my left arm just absolutely burns soooooo bad.

I know I've lost a little fuel before but holy cow changing a filter but I swear it stopped flowing. I don't think that's normal. I had to revisit the manual to see if I was doing it right, and I was doing it exactly by the book. I'm watching tutorials on YouTube as a sanity check and on all of them the fuel stops coming out the tank side. It kept coming out the tank like a little hose siphoning gas so long as I had the filter disconnected.

 

[Scottydoggs]

that heater circuit code wont affect the reading. and its down stream. o2's have a built in heater to get them warmed up faster. down stream sensor dont do a whole lot in regards to the fueling.

have you been tuning on it yet? or just scanning with the hpt? if you have tuned it some. go back to the stock file. re flash it and see where your at.

 

[Matthew Jeschke]

Any idea why that doused me in fuel like that? Shouldn't the pump stop that from happening? Is it cause I have a poorly sealed gas tank or something? idk... Never experienced that before changing a fuel filter.

 

[Matthew Jeschke]

@Scottydoggs been tuning it for a couple years now. Running speed density... fuel was spot on a few weeks ago.

I'm going to give this an adult dose of fuel injector cleaner... It also dawned on me, due to fuel rail design, the fuel comes in closer to bank 1 so if the pump doesn't provide enough volume then bank 2 will be slightly lean (there's more volume between bank two and the pump than bank 1). The first component is the pressure regulator... so if that doesn't resolve my issue then I think I may have a bad pump. Otherwise, I have no way to check the pump pressure because I don't have the right fittings in my tool kit to connect to that side of the pump

Thinking out loud, if the check ball is good, I would expect rail pressure the pressure to drop a bit when ignition and pump are turned off as the rail equalizes with the return. However, I see it bleeds down over time to around 30 PSI. I'll probably leave the gauge on overnight to see if the pressure goes to zero in which case the pump checkball is certainly bad.

 

[Scottydoggs]

Any idea why that doused me in fuel like that? Shouldn't the pump stop that from happening? Is it cause I have a poorly sealed gas tank or something? idk... Never experienced that before changing a fuel filter.

they all do that. its just some syphon action. right to the arm pit it all goes lol

 

[Scottydoggs]

@Scottydoggs been tuning it for a couple years now. Running speed density... fuel was spot on a few weeks ago.

I'm going to give this an adult dose of fuel injector cleaner... It also dawned on me, due to fuel rail design, the fuel comes in closer to bank 1 so if the pump doesn't provide enough volume then bank 2 will be slightly lean (there's more volume between bank two and the pump than bank 1). The first component is the pressure regulator... so if that doesn't resolve my issue then I think I may have a bad pump. Otherwise, I have no way to check the pump pressure because I don't have the right fittings in my tool kit to connect to that side of the pump

Thinking out loud, if the check ball is good, I would expect rail pressure the pressure to drop a bit when ignition and pump are turned off as the rail equalizes with the return. However, I see it bleeds down over time to around 30 PSI. I'll probably leave the gauge on overnight to see if the pressure goes to zero in which case the pump checkball is certainly bad.

im not sure what check ball you speak of, but every car or truck ive owned f/p drops after sitting. likely why the pump primes the system with the key to run, then it dont turn back on till the engine fires up.

you might have a small vac leak on the one side?

any mods done? cam headers ect? really no need to just be SD/VE (what ever you like to call it) tuned if its na still. thats a boost thing due to out flowing the maf.

have you checked for vac leaks? intake to heads, tb gasket, injectors and their o rings, pcv lines evap lines. spray em all with flammable brake cleaner or starting fluid, or propane works too. if the idle jumps up when sprayed you found the leak area.

 

[Matthew Jeschke]

Worked on it for a few more hours.

Quite a lot of mods: However, essentially it's a LQ9 6.0L w/ cam and flex fuel injectors (bit I think 32# / hr instead of 24# as I have it setup).

NO Vacuum Leaks: Tested using your starting fluid method. Great tip! And I didn't even blow myself up!

FOUND exhaust leak (but likely not issue) it's where I'd expect, I welded my muffler in and the welds suck they started leaking again. I know it runs like crap with any exhaust leak. Maybe part of contributing factor.

NO misfiring cylinders: Checked to make sure all the cylinders are firing... if they weren't it runs like crap... but it's running smooth. Anyways, I did a spray water test, PASSED. Then I used a heat gun to see temps all 8 cylinders are around 260F

Fuel System Cleaner: No affect. Ran for good hour at idle. Add 3x perscribed amount 24 oz of lucas injector cleaner in tank.

NO Start after sitting: Note let is set for 15 minutes after running for 45 to get cleaner through system. It wouldn't start. I presume there was no pressure in the rail. I had to turn key of and on several times and multiple attempts cranking to get it to start. Once started it runs w/o stalling and at correct AFR> Rail pressure dropped to zero after sitting. I thought there was a check ball in the return line, so if pump turns off the pressure it held in the rail. That way, there's some fuel left in there when you start the truck again and pump doesn't have to purge air from the rail / lines? I'm likely confused, I know enough about fuel systems to be dangerous.

No gas in oil: Note the oil seems good / not washed out with gas. Kind of figured this would be issue if injectors are leaking into cylinders.

 

[Matthew Jeschke]

Think I found it.... the tune file is corrupt! Editor likes it but PCM does not... when loaded to PCM it WON'T read VE table correctly.

No matter what I set in the VE table it has no affect on fuel delivery (this is where you adjust open loop fuel in speed density mode). My Fuel trims showing about 20% lean... even if I add 40% more fuel, they're still 20% lean. I switched to a baseline LQ9 file and no issue there. I also switched to my baseline LM7 file and no issue there. However, I have two years of tuning in the current file. Trying to figure out how to save it. I tried copying it to a one of the baseline tunes but didn't work. Somehow there's a overflow or something in the Tune file that shows in the editor and copy/pastes fine but the computer doesn't like it. This is going to be a real trip trying to find somebody who knows how to fix this.

 

[Matthew Jeschke]

I want to test pump pressure at this point. Not making much headway with the HP Tuners stuff. Unfortunately, my fuel test kit doesn't have the right fittings to even rig something up to test the pump. The parts store doesn't rent anything that would fit either.

I'm looking for a fitting that'll allow me to plug in on the pump side before the rail / regulator, right there where the line clips into the rail. I want to disconnect the rail and hookup a pressure gauge to the line going down to the filter & pump.

I'd also like to be able to have a T that patches into the pump and rail... ad well as return and tank (pump?). If possible.

I think the FSM just calls for pump pressure though so that would suffice.

Long story short, anybody know what size the fittings are for those lines? I'm looking at this Deluxe Fuel Injection Service Kit from Harbor Freight. Not sure if it'll fit?

https://www.harborfreight.com/deluxe-fuel-injection-service-kit-58817.html

Here's a video of what I'm thinking to do to test pump pressure:

New video by Matthew Jeschke

photos.app.goo.gl

 

[Matthew Jeschke]

I replaced the fuel pressure regulator. Going to log some tuning data to see if it changed injector trims. My guess is not.

I'm still unable to figure out what size the fuel line is coming into the rail, that is line from pump to rail by pressure regulator. I need to find an fuel test fitting to plug in my pressure gauge so I can verify pump pressure. Once I know pump pressure is good I'll rest a lot better.

UPDATE: Pretty sure the pump is bad at this point. I'm going to swap it out under warranty. I replaced the fuel filter, and fuel regulator... Rail pressure for key on ignition off is still at just under 50 PSI. FSM says it should be 58 to 62 PSI. I tested with two separate fuel pressure gauges. I also realized it's a Delphi part. I've had nothing but problems with Delphi parts... Maybe why this comes with a lifetime warranty? In hindsight should have bought a AC Delco or Walbro pump from summit racing.

 

[Matthew Jeschke]

I want to scream. Swapped in a new fuel pump. It's safe to say the rest of the system is good as I've either replaced it all and or inspected it. EXACT same pressure Key on Ignition Off. Revving the engine is EVEN worse, drops to 40 PSI. Seems Delphi is selling complete JUNK, their OE replacement parts don't even meet factory spec. I need to figure out how to return this warranty replacement and buy a real pump instead of this junk.

Anybody else know of a decent brand of fuel pump? I was thinking warbo HERE

In the meantime I need to call Delphi if possible and see why this doesn't meet spec. If there's something I'm missing.