Good evening all! Hope everyone is doing well. I have recently begun experiencing an issue on my 2003 F150 SCrew with the 5.4l. When accelerating from a stop or hitting a bump the truck will stall. This is not a miss as I have experienced these before. It is more like the engine is losing all electrical power. I have done the wiggle test on all connections and wires I could find both under the dash and in the engine compartment. I have also checked the ground straps and made sure the battery is good. I have checked the connection to the crankshaft position sensor. I did find my connection to the ignition switch a little loose and snugged it up. At this point I am thinking the ignition switch or lock cylinder is to blame since when the issue occurs it resembles the key being switched off (the engine looses power and gauges all zero out). Has anyone experienced this before? Any other ideas as to what could be the issue? As always, thanks in advance for the help!

 

I'd throw a PCM Power Relay at it and see if it sticks.

 

Just the engine and nothing else is losing power?
Do you have a heavy key ring?

 

Yes just the engine. No, I do not have a heavy keyring.

 

Just an update on this. I replaced the altenator this week, but the problem is still there. While trying to keep it running after work yesterday, I pushed down on my cold air intake and was able to replicate the stumble/ wanting to die! I am going to take it apart starting at the air filter and clean and inspect every thing until I find the issue. It seems as though something is causing the engine to get too much air or a severe restriction in air flow. Anybody seen anything like this before?

 

while your at it clean your MAF sensor with the appropriate cleaner

 

Just an update. I cleaned the MAF, throttle body, and my K&N filter with the appropriate cleaners. I did notice quite a bit of dirt coming off the MAF and the IAC. The issue seems to have gone away, but my idle just doesn't seem right. When coming to a stop it will idle at 900rpm for about 30 seconds then drop down to 600rpm. I am thinking the issue is still the IAC.

 

Clean the IAC so the inside pintel is free to move against the spring and diaphragm.
If this does not fully solve the idle, replace the IAC. There is an air bleed hole in the diaphragm you cannot get to for cleaning.
Check the crank sensor plug for seating.
Good luck.