Hey guys I have a 06 Screw with 5.4 so far 155k trouble free miles, until today. Let me start by saying about a year ago I had the truck go into "engine failsafe mode" no power and it quit running...I threw it in neutral and restarted right away with no other issues. Fast forward to today, I let it warm up 5 minutes as its cold here, get out on the road and try to get up to speed and she starts bucking. I came to a light and stopped to make a right and she died again, restarted immediatley and got home. Anytime I tried to give it more than half throttle it would hesitate and buck. If I went easy I can reach any speed and the engine is smooth, cruising 70 its smooth try to accell to make a pass and it starts bucking hard. Smooth as silk at idle and never threw a code. Tune up was done at 135k with motorcraft parts.

Truck has been factory stock its whole life....

 

Specifically what was replaced in the "tuneup"? This sounds like it could be bad coils, clogged fuel filter (change every 30k!), defective plugs, a bad tank of gas, or dirty fuel injectors. The fail-safe is often caused by a dirty throttle body, has it ever been cleaned?

I would get it scanned for any OBD2 codes, both hard codes and pending codes.

 

How many miles on the plugs? has the throttle body and MAF ever been cleaned?

 

The tune up was plugs and coils, motorcraft. Plugs have around 25k miles on em. Maf has been cleaned but not the throttle body. I changed the fuel filter at 100k so it needs to be done again. I just drove it up to refill my propane tank maybe half a mile distance, and now it barely wants to run. Doesnt feel like a miss, more like the engine quits for a second and picks back up then dies again until I let off the throttle and itll idle for a minute before it quits running.

I have to wait for my buddy to bring over his fuel pressure gauge.

Still no codes

 

Most throttle bodies need to be cleaned at about 100,000 miles. A dirty one can send the engine into failsafe mode.

 

Depending on where you are(corrosion), could be the FPDM needs replacing.

 

1. Need a scantool to read the FP PID - no Schrader valve fer a gauge.

2. You need a good scanner to pull pending / Mode $06 misfire codes

3. FPDM: https://www.f150online.com/forums/ar...placement.html

MGD

 

Is this good? Lol I think i found the problem

 

Bingo!

Replace with a Motorcraft FPDM, not Dorman if ye can, and don't fergit to use them standoffs.

MGD

 

Got the new one on with the updated bolts to hold it off the frame. I coated the underside with some grease also. I went ahead and cleaned the TB and MAF threw a new fuel filter on. Shes back to running good.

Thanks Guys!

 

Glad you got it fixed!