2003 F-150, 5.4, 4WD.
87,000 miles

While driving, any speed, highway or city.
It will suddenly go into a mode that will not allow it to accelerate.

I'll pull over, shut it down, wait a second, restart and its off like a rocket again.

Could be 5 minutes before it happens again. Could be an hour... No pattern there.

Replaced filter. Not the problem

TPS?

The RPM will litteraly go down the more you push on the pedal.
I tried holding the gear manually, and got the same thing. Doesnt seam like its the trans, deffinitely motor issue...

Any help appreciated.
Thanks,
Eric

 

It runs fine, drives fine and idles fine at all other times. No stalling either.

 

I had the same thing happen to me on my 2000 Mustang a year or so ago. I had hit a chunk of asphalt on a county road that was in really bad shape and it had bent my intermediate exhaust pipe in, creating too much back pressure. It was at random times that it would just fall on its face which i found quite weird.

...just a thought, but the issue sounds really similar. Could give the exhaust system a once-over.

 

Double checked the exhaust. Everything looks good under there.
Thanks.

I should add:

Before I figured out I could re-set it with the ignition, I drove it about 20 miles and it didnt seem like it was going to fix itself unless you turned it off.

I floored it and it down shifted, but slammed on its face... no acceleration at all.

 

Have you scanned for OBD2 codes?

 

I did.
I was on a 150 mile trip to visit the in-laws when it started doing it. I swung into a mechanic friends shop and he scanned it.
Said there were 3 codes and then cleared them.

I picked up a scanner at the parts store and am waiting for it to set the codes again on the trip home today.
I'll try to be more specific once it sets the odes again...


In the 150 miles it did it the first time about 60 miles into the trip and then abuot 120 miles into the trip.
Once I got to our final destination it seemed to do it way more often while driving around town.

 

Post the exact P-numbers, please.

While you are waiting on codes, follow the hose from the PCV valve to the back side of the intake, under the throttle body. The elbow is famous for rotting and cracking, causing a vacuum leak.

 

Just got back.
It did it 4 times in the 150 miles. This time while still rolling down the freeway I put it in nuetral, killed it, fired it back up and off we went without skipping a beat.

It has 2 codes this time.
P0171 and P0174.
Lean bank 1 and 2...

I checked for vacuum leaks were you suggested and everything looks to be in pretty good condition.
I dont hear any whistling and it seems to idle smoothly.

Whatta ya think?

Thanks,
Eric

 

Fuel Pump?

 

Somthings re-setting though...

Turning the key off and then re-starting immediatly fixes it everytime.
Fule pump seems unlikely.

 

Yeah your probably right, our old suburban is doing something similar tho and it is the fuel pump. Random times it will just loose all power...but that was a common issue in a lot of gm vehicles around its model year, not a ford problem.

I think I've replaced 3 fuel pumps in gm vehicles around the same year as our suburban come to think of it haha.

 

Lean both banks is USUALLY a vacuum leak. However, your fuel pump COULD be on its way out. You should probably do a fuel pressure test.

 

I'll give it a shot and let you guys know.

Does it makes sence that it would be fixed with a re-start?

Thanks for the help,
Eric

 

Do you make it a habit of running the tank lower than 1/4 before getting gas? If so, that can reduce fuel pump life, it depends on fuel in the tank to keep it cool.

 

Ya.... I would probably say I do. Deffinitely no higher than a quarter tank for sure.