Incorrect fuel pressure Key on and Engine Running

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.

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.

@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.

Matthew Jeschke said:

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.

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

Matthew Jeschke said:

@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.

Click to expand...

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.

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.

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.

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?


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

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.

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.