Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Diagnosing my uncles truck. He had it smogged in April. I have the emissions test results. The only gas that is high are HC's
He recently replaced the injectors and did plugs and wires cause the truck was running bad. Well after the repairs the truck ran fine according to him. Well a few weeks go by and the truck starts running bad again and eventually ceases to run. Well I come look at it and hook up a fuel pressure gauge and find that it builds 50 psi of fuel pressure but quickly goes to zero when the pump shuts off.
So I open the throttle plate and see a bunch of fuel spraying into the intake. Well we remove the intake and find the fuel pressure regulator spraying fuel out of the vacuum side. So we replace it and no more fuel spraying out and put everything back together. The truck fires up now and runs but misfires. I hook up my scan tool and see the short term fuel trim -30 on both banks. And I check fuel pressure and it's 0psi. Wth this doesn't make sense. Any help is appreciated.
Welcome to the forum, thanks for posting!
It sounds like there's a leaking injector or leaking fuel pump check valve. You'll want to block the return line to the tank and see if the fuel pressure continues to bleed down. If it does, then you know there's a leak from one if the injectors. If it doesn't still bleed off, then the fuel pump check valve is to blame.
Check out this lecture for a description of both scenarios and tips for troubleshooting.
johnathon.balderas wrote: So I open the throttle plate and see a bunch of fuel spraying into the intake. Well we remove the intake and find the fuel pressure regulator spraying fuel out of the vacuum side. So we replace it and no more fuel spraying out and put everything back together. The truck fires up now and runs but misfires. I hook up my scan tool and see the short term fuel trim -30 on both banks. And I check fuel pressure and it's 0psi. Wth this doesn't make sense. Any help is appreciated.
Sorry, didn't know you were still posting!
The ruptured regulator explains the pressure bleed down, looks like you got that nailed down.
As for the 0 psi reading, if the truck is running I'd not trust that gauge. The negative fuel trims seem normal based on the extra fuel leaking into the intake and may need time to relearn or may need to be reset.
Also, there's the possibility of fuel contaminated oil from the leak. This could cause a rich condition and negative trim numbers due to fuel vapor being breathed in through the PCV system
"Ground cannot be checked with a 10mm socket"
The following user(s) said Thank You: johnathon.balderas
The fuel pressure isnt bleeding down anymore it just is non existant. I was getting 50 psi when pump was running and then it would drop to zero after punp shut off so i found the regulator not just leaking but spraying fuel out. So we replaced it and no leaks but I hook my gauge up now and I get zero psi.
Ok the fuel in the crankcase makes sense. I noticed that when the truck was idling the oil pressure was really low and my uncle said that he never saw it dip that low. So I'm advising my uncle to change the oil and then we can go from there.
Thank you Noah for the fuel contaminated oil idea. Oil change was right on the money. Fuel contaminated oil crossed my mind but having not seen it personally and not realizing it could cause that rich of a condition I dismissed it. Thank you everyone
Last edit: 8 years 9 months ago by johnathon.balderas.
Topic Author
