Matthew Jeschke
Full Access Member
I HAVE to know EXACTLY what failed on my truck so it won't happen again and strand me in a remote location of the mountains I use my truck in. Any additional thoughts are appreciated!
Symptom: failure #1 driving slow speed (low power) for some time. Engine leaned out and stalled. Waited one hour, engine started no problem and ran fine. Failure #2 cruising on highway at 75mph engine leaned out and stalled. Waited 20 minutes drove 1/4 mile and same effect. Waited hour, still wouldn't start. Waited 2 hours still wouldn't start. Waited overnight started and ran like a top. On second failure I was able to hookup my tuning suite as well as wideband (although connector broke to log the wideband) while waiting for tow truck and diagnose a bit. The AFR starts at around stoichiometric (14.7:1) if I try to move the vehicle it leans out and stalls right away. If I let it idle it would go from 14.7:1... onto 20:1 then stall. I assumed rail was getting pressurized but pump couldn't keep up with demand. Oh and also cannot smell gas out exhaust when trying to start and it won't.
I bought a AEM 50-1200. My engine is a LQ9 (built no doubt) but assuming power on low end is 350hp factory for that engine that comes stock with a 140LPH pump. Pump I have is a 340LPH pump. Excess fuel pump flows gets returned to the tank.
Boiling Fuel? One consideration buying pump was that it didn't flow too much, and boil fuel. If return sends too much fuel back to tank it will sync temperature with engine in tank and boil the fuel. I called AEM when I bought pump and they thought would be appropriate size for my truck (I see other people using same pump on similar builds). I also called and asked same question when having issues. They thought of that but leaned towards a defective pump.
Bad Regulator: I have a brand new 57psi regulator and return style rail. When had issue I pulled the reference line off intake and tried to start it. Didn't work. No fuel coming out of regulator reference line either. Tapped on regulator (thought maybe stuck) no effect. Am told when the regulator fails it creates a rich condition.
Sticky Injectors: no trouble codes are tripped. Problem is intermittent. When running correctly I can log data in my tuning suite and all trims are spot on. Engine runs PERFECTLY smooth.
Electrical: swapped relays around under hood. No blown fuses. Battery voltage is correct, 12.6V (assuming alternator good as result ~ dash shows 14V when running). No blown fuses (checked ignition) and all others.
Hot pump: I tried to feel if pump was hot. I reached up top of the tank and felt the connector as best I could, seemed normal. Felt the relays and fuse under hood no hotter than expected. I also felt under tank near pump sending unit. Felt normal (unsure if that would give any idea though).
Pump Sound: pump sounded a bit labored when I turned ignition on after failure #2. I have a bit of an odd smell too. Cannot tell where the smell is coming from. I want to say it's an electrical smell but cannot say for 100% certain. The harnesses are all good though and I upgraded to 12 gauge wire.
Sending unit pump hose clamps: I was sold screw type clamps. Didn't occur to me those can loosen over time. When I diagnose / swap parts in tank I am switching to clamp style. However, don't think clamps are issue as that would be a 100% no start condition.
I suspect it's a bad pump so does AEM but I don't have a means to verify it's the pump before I hit the road again.
Symptom: failure #1 driving slow speed (low power) for some time. Engine leaned out and stalled. Waited one hour, engine started no problem and ran fine. Failure #2 cruising on highway at 75mph engine leaned out and stalled. Waited 20 minutes drove 1/4 mile and same effect. Waited hour, still wouldn't start. Waited 2 hours still wouldn't start. Waited overnight started and ran like a top. On second failure I was able to hookup my tuning suite as well as wideband (although connector broke to log the wideband) while waiting for tow truck and diagnose a bit. The AFR starts at around stoichiometric (14.7:1) if I try to move the vehicle it leans out and stalls right away. If I let it idle it would go from 14.7:1... onto 20:1 then stall. I assumed rail was getting pressurized but pump couldn't keep up with demand. Oh and also cannot smell gas out exhaust when trying to start and it won't.
I bought a AEM 50-1200. My engine is a LQ9 (built no doubt) but assuming power on low end is 350hp factory for that engine that comes stock with a 140LPH pump. Pump I have is a 340LPH pump. Excess fuel pump flows gets returned to the tank.
Boiling Fuel? One consideration buying pump was that it didn't flow too much, and boil fuel. If return sends too much fuel back to tank it will sync temperature with engine in tank and boil the fuel. I called AEM when I bought pump and they thought would be appropriate size for my truck (I see other people using same pump on similar builds). I also called and asked same question when having issues. They thought of that but leaned towards a defective pump.
Bad Regulator: I have a brand new 57psi regulator and return style rail. When had issue I pulled the reference line off intake and tried to start it. Didn't work. No fuel coming out of regulator reference line either. Tapped on regulator (thought maybe stuck) no effect. Am told when the regulator fails it creates a rich condition.
Sticky Injectors: no trouble codes are tripped. Problem is intermittent. When running correctly I can log data in my tuning suite and all trims are spot on. Engine runs PERFECTLY smooth.
Electrical: swapped relays around under hood. No blown fuses. Battery voltage is correct, 12.6V (assuming alternator good as result ~ dash shows 14V when running). No blown fuses (checked ignition) and all others.
Hot pump: I tried to feel if pump was hot. I reached up top of the tank and felt the connector as best I could, seemed normal. Felt the relays and fuse under hood no hotter than expected. I also felt under tank near pump sending unit. Felt normal (unsure if that would give any idea though).
Pump Sound: pump sounded a bit labored when I turned ignition on after failure #2. I have a bit of an odd smell too. Cannot tell where the smell is coming from. I want to say it's an electrical smell but cannot say for 100% certain. The harnesses are all good though and I upgraded to 12 gauge wire.
Sending unit pump hose clamps: I was sold screw type clamps. Didn't occur to me those can loosen over time. When I diagnose / swap parts in tank I am switching to clamp style. However, don't think clamps are issue as that would be a 100% no start condition.
I suspect it's a bad pump so does AEM but I don't have a means to verify it's the pump before I hit the road again.
