2005 5.4 3-valve. Truck will idle for a long time just fine but will drive about 1/4-mile before it stalls & dies. Also if I rev it in place at around 2000rpm it will run fine for about 30-seconds and then stall. Wasn't throwing codes at first but after stalling it about 6-times it finally threw a P0171 & P0174, both banks lean.

I have Forscan so I can monitor engine data live. Here are my observations:
-The Long term fuel trim is pretty high. At idle it's around 10% but running the engine at 2000rpm it will get up to about 25%
-Fuel pressure is steady between 38-40psi and the fuel pump duty cycle is about 20-25%
-VCT error % is very small and they appear to be working normally
-Timing advance is pretty steady and doesn't do anything weird when the O2 goes lean
-The PCM will detect misfires when the truck stalls
-There is a parameter "fuel injector fault" for each injector. All of those will show faulted when this happen. Not sure what that mean

Right before the truck dies the O2 sensors go full lean, the short term fuel trim % starts going up and the truck stalls. Before that the short term will be very steady and the O2 will be switching like normal.

Any ideas? I first thought fuel filter but the fuel pressure is steady throughout.

MAF reads 0.03V with the engine off. I watched a video by Forktechmakuloco where he talks about that being an issue. I swapped it with a known good MAF from another truck and it didn't seem to do anything. During running the MAF is pretty steady, no odd blips when the truck goes lean & stalls.

No vacuum leaks that I could find and typically that would show up at idle, not higher rpm/lower vacuum conditions?

Thank you!

 

If you have a known good truck to swap parts from I would swap the throttle body. Very possible the throttle blade is not in sequence with the stepper motor and the feedback is incorrect. Do a KOEO test and listen to the throttle body.

 

Since the issue only happens during an engine load I'd still suspect a fuel delivery issue, your readings while within specs are on the lower half. It still could be an intermittent pump, clogged filter, or a fuel pressure regulator issue. If you feel the fuel delivery is not an issue then you might want to look at the possibility the catalytic converters are clogged.

Specs:
Key on, engine off 240-310 kPa (35-45 psi)
Engine running 193-310 kPa (28-45 psi)

 

Have you inspected the fpdm on rear axle since it controls the fuel pump/they are a high failure rate . How did you check for vac leak ,I would try a homemade you tube smoke machine .
I would be cleaning throttle body just in case ,try running it with snorkel off maybe plugged somehow . . After that I would be looking at plugged injectors ,contaminated fuel . Never hurts to test and clean injectors .If fuel filter not changed recently I would change it , look at fuel in a clear container . I don't know what work was being done last on the truck before this started .
Of course you are going to test cats , pressure test ,temp check ,maybe have someone feel volume at exhaust while you throttle up .
It must be dying because fuel ratio is so bad it can't fire. You do know 05's had bad series of injectors, I changed all of mine 100k ago . If they leak they can hydro lock and destroy engine . After 150k or so its a good idea to get new not reman injectors as they are high duty cycle and have to respond to milla sec pulse with commands to adjust fuel . But they are not cheap -nor do you want cheap . You can do a you tube test and clean station
Also the factory TB series was bad ,mine became intermittent at 60k . Mine kept going into limp mode . So yes an oem TB maybe a good thing , I tried reworking mine to no avail . Just make sure you get the updated version .

 

Your fuel trim is- it negative or positive , it trying to add fuel or reduce fuel .

 

Did some more tetsing this morning. Decided to change fuel filter since it looked pretty old and only cost $12. Old fuel filter was definitely restricted but I could still blow thru it.

Also pulled off the Fuel pump module back behind the spare, had some light corrosion but the aluminum plate looked fine once I cleaned it off. Frame where it was mounted still had paint and not rust. Electrical connector looked brand new when I pulled it apart.

Also reset the PCM.

Watched the throttle commanded vs actual position and it seemed to track perfect.

After restart the Long Term Fuel Trims went nice and low, down below 5% at idle. Driving around the block the truck ran great, revved up to 4k rpm, long-term fuel trim stayed around 10-12%. Thought I had it licked but I went for a little bit longer drive and it started doing the same thing again. This time once it died while driving it wouldn't restart. Had to push it down the street back to my house. I'm starting to wonder if this is temperature related as yesterday I was running the truck in hot afternoon (100F) this morning it was a lot cooler.

When the truck dies the MAF reading is smooth and follows RPM so I don't think it's throttle related.

I see this thing doesn't have a fuel return, can vapor lock become an issue when the fuel rails get hot?

 

When it would not restart ,do you think it is lack of fuel or what .Can you get it to start on starter fluid . It would not hurt to dump clean fuel rails -test injectors . Do you think you could be losing 12vdc positive to injectors or some of them . Pcm supplies a grd to each in pulses to trigger them at the right time -the right spray for milliseconds. . One signal lost to an injector could not shut it down but a common 12vdc pos loss could .
Check your crank sensor connection under engine ,any damage to that cable can shut it down . It is a frequent failure point and contains a shield that can ground out the signal . Monitor 12vdc pos on injectors with a test light to see if its string is dropping out. But I realize you don't have misfire indications either, you have fuel ratio problems .So we are back to lack of fuel or too much oxygen drawn in . ? Vapor lock at 100 degrees -I have my doubts . Is your tank full, you are not using e85 are you , can your fuel lines be getting near a very hot exhaust ? No reason for your system to be getting air bubbles when fuel pump in fuel tank under fuel . but just maybe your tank vent solenoid or carbon cannister is plugged or restricted . We need to pin it to just lack of fuel or not .
You have to let air in tank to get fuel out,this usually shows up if tank is hard to fill . Mud and insects have been known to cause this . See if your purge valve on fire wall is closed by blowing thru it ,it only opens on command .
You are correct this is a no return to tank fuel system , the fpdm controls everything with pcm oversight . The fuel rail pressure sensor is also vac assisted for acceleration I believe. The fpdm should be on standoffs to reduce electrolysis. If you have access to another try replacing it .
I'm reaching here ,interesting problem .

 

Here’s a pic of the PIDs when it dies.

listed from top to bottom
-Long term fuel 1
-Long term fuel 2
-short term fuel 1
-short term fuel 2
-o2 voltage 1
-o2 voltage 2
-engine rpm
-fuel pressure.

about halfway thru you can see the o2s flatline and the short term skyrocket. This is when it dies. I’m either loosing fuel or all of the injectors are losing power to fire. Don’t think it’s an air issue.

how would you monitor voltage to the injectors? Would I have to cut into some wiring? On my diesel it’s got a dedicated module for the injectors that runs at 48v and you can monitor that voltage thru the computer.

This is revving it up in park btw.

 

Injectors have pos 12vdc standing on red wire of injector plug with key on . you need a small probe like a paper clip to put in there

 

You can monitor the injector voltage at the injector fuse.

(More useful data if you can monitor the injector circuit CURRENT at the fuse if you have access to an amp clamp and a scope.).

Can your FORScan display any injector data?
How about that “fuel injector fault” in post #1?

PS.... Calling all experts: Isn’t there a common problem with the fuse box fuse for the injectors, or is that for the fuel pump fuse, on these mid-year trucks?

 

There's a parameter in Forscan called "Injector Fault". It just shows true/false. They have a general one and one for each injector. All of them showed fault when it died at the same time. I wasn't sure if that actually meant electrically they faulted or the PCM just thinks they aren't working because of the engine dying.

 

The injector feed breaks off into separate groups ,I was thinking there could be a weak connection somewhere there or at least rule it out. I would wiggle wires during test .

 

Hey guys I figured out the problem!!! I took the suggestion of wiggling wire connectors and found one that would consistently make the truck die. It’s a 12 pin connector right in front of the pcm. I’m guessing one of these wires is the power for the injectors as I was seeing all injectors fault at the same time when the engine would die.

Pulled the connector apart and found some bent pins. Also the plastic lock on the connector was broken and it was engaged fully. Bent the pins back, put in some dielectric grease and got it fully seated. Truck now runs great! The connector isn’t “snapped in” but I tugged on it and it doesn’t seem like it’s going to come apart rolling down the road. I tried putting a zip tie around it but couldn’t find a good way to lock it in.

Another clue. The oil pressure gauge had been reading zero for a long time. Truck obviously has oil pressure so we tried changing the sensor which didn’t fix anything. When the truck started this stalling the oil pressure gauge started coming back at times. Fixing the connector also fixed the oil pressure gauge.

 

Glad you found it . That connector looks nasty I will research that when I get time .Be prepared to solder a new one in one day with heat shrink or liquid insulation . I just don't like the looks of it for long term .

 

I had just sprayed the connector with electrical cleaner when I took the photo. It didn't look too bad once it dried out. Now covered in dielectric grease so hard to get a good photo of it now.

Also in the first picture you can see how unplugged the connector was. Probably a good 1/4-1/2" unplugged. Gotta find a good way to lock that in. Tried a zip tie which was fine on the top, but at the bottom the wires are super close together and I would be pinching some which seemed counter-productive.