2003 F150 5.4, got a new jasper engine last year with new plugs. Everything has been great till last month. Truck started falling on its face after warm up and timing shows -3 to 0 deg when its doing it. If you cycle the key runs fine again for 10-20 minutes then acts up again and the cycle repeats. Fuel pressure is 35-40 even when acting up, has gotten a new fuel pump, test pcm, camp sensor, mass air flow sensor, knock sensor, idle air control and throttle position sensor all replaced trying to find the issue. It always idles OK even after acting up, always starts easy even after acting up and cycling key. Have also replaced air filter. Seperated exhaust post o2 sensor to rule out cats, replaced 1 up stream o2 sensor no change in data. Not sure what to try or check next. Engine runs great for 20-30 minutes falls on face during acceleration, when this happens timing shows retarded. I pull over restart and truck is great for another 20 minutes. I have also jiggled and pulled on harness checking for loose connection no change. No CEL when engine won't accelerate and it falls on its but. Thinking of buying a new coil and swapping to see if a difference can be made. Don;t think there is an injector issue as fuel pump maintains 35 + psi even when acting up. Any ideas would be appreceated.
Thanks

Quick update
Truck is running with exhaust disconnected post 02 sensor but before cats. Have checked crank for thrust. Inspected tone ring with camera. Replaced knock sensors, fuel pump (min psi 35 even when acting up), cam, crank sensors, idle air control, 1 02 sensor and mass air flow. Inspected plugs and coil connectors and have tried test pcm. Result is always the same runs 20-30 minutes looses power won't rev past idle ie truck always idles fine but when given gas falls on it's face). A quick key cycle even with out stopping truck and truck runs great for 20-30 minutes and repeat. Truck has not thrown a code in a couple weeks since testing started. Looking at log file after driving nothing drops out or changes except spark advance normally around 11* at idle drops to maybe 1* at idle and goes -3 to -4* if you try to accelerate when it acts up Have pull tested harness at every connection and possible rub spot, no changes on log file while doing so and can not make truck act up or stop acting up while doing so. No CEL makes me think mechanical issue but a quick key cycle always allows truck to drive fine for 15+ minutes after. Have also used smoke machine to check for vacuum leak. Have plugged ports to pcv at intake no change.AC on or off no change.

7/30 UPDATE
Figured since I don't have any CEL fault has to be mechanical. Left fuel gauge on truck and drove it till it acted up. Found when truck acted up fuel pressure dropped to 10 psi close to 0 when under load. Found my primary cause. Considering truck got a new fuel pump after issue started we replaced fuel filter and checked filter while changing was pretty old was due anyways. Found when truck was at idle pulling vacuum off regulator made no diff in PSI. Only testing I could find on motor showed regulator to be bad. If at 2000 rpm psi was a gradual drop to check fuel filter or restrictions. Installed fuel psi regulator and condition has improved but truck is not fixed. Step 2 ran ground and hot from battery and by passed fuel shut of switch and fuel pump relay, no improvement. Either way still making progress just need to find my PFP. I'm down to restriction in fuel line or bad fuel pump. New fuel pump was from auto zone so won't be shocked if thats the issue. Either way look to have this fixed next week.

 

The computer adjusts the timing based on O2 sensor, ambient temp sensor, engine temp, maf sensor, throttle position, and may be other stuff. One or more of those could be the problem seems to me including the PCM. #not a mechanic. Seems to me you need a good diagnostic technician to take a good look at it.

 

Timing begins at the Crank Sensor.
I would be looking at the Sensor plugup seating.
BTW, this motor uses 8 coils.
If you had a misfire in ignition, a code would be set.
P030X misfires.
P035x for faulty coil electrical issues..
If the Crank sensor cannot feed timing reference to the computer, the computer cannot set any code if it can not cycle through it's program to see any fault.
The issue could even be the timing wheel the Sensor has to track, being a rebuilt motor. It's behind the front pulley and may have bent fingers or even loose.
Good luck.

 

Thanks Bluegrass
I has that thought or maybe even small crack in crank sensor or cam sensor causing an issue after warm up so we put new crank sensor in this am and used inspection camera to check inside, no issue found. Still acts up with new sensor and returns to normal with quick key cycle. We haven't gotten any faults other than a knock sensor fault a while back witch leads me to think it's mechanical and not an electrical issue. Maybe I'll get luck and lightning will strike it down later today.
Thanks for the suggestion

 

Fix the knock sensor. That can retard timing if it thinks it's knocking.

 

Knock sensor was replaced, inspected harness and have done a pull test on harness trying to make truck mess up with no luck. Have not been able to get truck to act up when pulling harness or run right after its not running right by moving harness either. No fault has retuned for knock sensor since replacement.

 

After all you have done, I would go back to the Cats or muffler/tale pipe for being restricted as they heat up over the time period indicated.
Stopping motor then restarting it clears variable short term tables involved with controlling a running engine moment by moment and allows restriction condition to fade , only to return as the motor gets more restricted in breathing.
Ignition timing is one of them as it continuously changes in response to load, throttle, temperature changes and other inputs.
Retarded ignition timing in itself is not a fault per sey but an indicator, unless something else is damaged to the point it sets a code. In those cases you still would have to determine the cause or it would happen again.
Good luck.

 

Exhaust is disconnected after 02 sensors and before cat. Makes for a very loud hot rod sounding exhaust but did not correct issue.
Keep um coming this is mortal combat going to a dealer now would be a huge let down.

 

i agree with others on getting some diagnostics. Throwing parts at this problem won't do it. you need a high end scanner to see what's happening and a knowledgeable person to run it.

 

I / we have been all over for you doing your guessing.
A misfire will cause ignition retard, an ignition knock will also retard as much 8 degrees until the Knock sensor does not 'sense' it any longer.
Your missing it somewhere.
Could have paid a good shop the same or less money to find it by now.
Good luck.

 

Were you able to resolve the problem with the computer retarding timing?