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2003 F150 5.4 4x4 4R70W Recently rebuilt engine, no apparent vacuum leaks with an engine off smoke test.... Smoke only comes out through the purge valve on the IAC and throttle body.
Currently, running TFT both banks about 28% at idle in park cold and at operating temperature. When I drive it at about 30mph TFT drops to about 2% (and it holds like that every time..., But once I get it up between 50 and 75 and trims got back up to 25-30%. All 4 o2 sensors oscillate like everything is normal, all the injectors and coils fire on time...
Would I be looking for both fuel and vacuum, or something else?
I won't have a fuel pressure tester until Wednesday or Thursday. Someone decided that they like mine more than I do so I had to order another one.
Have you reset the Keep Alive memory. And did you smoke test ths engine cold and hot?
I recently worked on a 04 F150 fuel trim numbers were acting weird as well. Turned out to be an intake leak, smoked it first thing in the morning. Give the smoke some time to work as well.
A quick fuel delivery test is to watch o2 sensors to make sure they stay rich on a wot run. Voltage should be up near 800mv and stay there with no dips.
What do the trims do in park holding at say 1500 rpms and 3k rpms?
The engine was smoke tested hot and cold, and with a vacuum gauge while the truck was running at idle I was getting 26in vacuum and 24 at 2000 RPM.
Sitting in park, running at 1500 and 3000 TFT goes to 8-10 and 16-18 respectively.
The post office finally did something right and got me my pressure gauge a day early.
KOEO It gets 30PSI
KOER 10 to 20 PSI
Disconnect the fuel pressure regulator from the vacuum line, Pressure goes back up between 20 and 30 and trims go to a normal range.
Put a manual vacuum pump on the pressure regulator and apply vacuum, and you can watch the pressure fall and Trims Rise steadily as the vacuum climbs...
Fuel pressures where checked at the frame before the filter and on the Schrader valve on the rail.
Also, fuel pressure drops in seconds (like 2 to 5 seconds) all the way to zero as soon as the power shuts off with no visible external fuel leaks. Check vavle in the pump maybe?
I have yet to do a current test on the pump fuse, but from all of this other info I figured out today, Im pretty sure the fuel pump is dying and just not giving the volume the engine needs to maintain the pressure while running.
Would that be a correct reading of this information?
Is there something else also happening here that I'm missing?
oh, it's low for sure.... spec is 37 to 43.... The fuel pump is definitely well on its way to kick the bucket after 315k miles.... I just didn't have a way to diagnose that when I started the thread.
But is there something else I need to look into? My understanding was that the fuel pump would change the trims at idle, but return to mostly normal at higher RPMs...
With a dying pump, the trims get worse with rpms because it is not able to supply enough fuel with the increase demand. The fuel trims numbers increase because of that lean response. The ECM is asking the injectors to stay open longer to make up for that lost fuel.
Before condemning the pump you can voltage drop test test the power and ground at the pump. You want to do this test with the pump running. Or you can load test the wires with a bulb.
High trims that get better with rpm would direct you to look for a vacuum leak.
Well the fuel pump dropped entirely dead the other day.... I had picked up a pump and sending unit from a salvage yard for other purposes, but since mine was dead, I figured I would put it in my truck, being that it was a Delphi pump and those usually never have any issues..... Wouldnt you know it, the same low-pressure issue already starting on this one. That makes me wonder if it's the pump or something else in the system. I'm going to build an adapter for my fuel pressure gauge on Monday when I get home so I can test the pressure directly at the pump. I can't really think of anything that could cause a drop in even the pressure in the system after the pump. It is no longer dropping pressure like it was, but it doesn't get up as high as its supposed to.
