About 350 miles into a 400 mile trip today, all of a sudden my truck started bucking when I gave it the gas. Its an '01, 5.4 w/40,000 miles. Its been absolutely trouble-free...til now. Cruising, its OK, but accelerating...its like it stumbles and misses. The more load I put on it, at a low RPM, the worse it is. Give it gas when its doing 45 or so and in O/D...and it feels like the motor is going to rock itself out of the chassis! On a 60's car, I'd say it was an electrical miss or a bad timong chain, but on this thing...I don't know. I just gassed it up about 20 miles before this started happening. It was a large, busy Shell station, but you never know.

Help, help...what do you guys think is wrong?

 

Computers haven't changed cars that much. Your feeling about an electrical problem could be right on. Missing under load is commonly a problem with secondary ign. wires. 40K is kind of early for this to happen but if one of the wires was run too close to something hot it could be breaking down earlier than normal. does it set codes ( check engine light come on ) when it does its missing. The computers are able to tell you which cyl. is actually dropping out. A bad ign wire or plug causing a miss will almost always turn on the light. A fuel filter would be an inexpensive insurance measure. good luck!!

 

The 'check engine' light does not come on. Also..I can rev it up in the garage, and its as smooth as silk. I'm gonna change the filter probably tomorrow...gotta buy the tool. Is the filter under the driver's seat, on the frame like the earlier F150's?

 

My vote is for dirty filter. Doesn't take much gas to rev an engine in neutral. The heavier you are on the gas while driving, the more gas the engine requires. The bucking and missing while accelerating, but having it smooth out once you let off of the gas and just cruise is a classic sign of fuel starvation.

 

Fuel filter is on the drivers side of the frame about middle of the truck. Probably a little closer to the rear tire then the drivers seat. Also, it's on the inside of the frame.

 

MROLDV8,

i had the same problem happen to me not too long ago. the computer didn't throw a CEL but it did give a misfire code in #4 or #6 (forget which). dealer changed coil pack and plug under warranty (happened around 30k miles), and the problem went away.

 

The same thing happened to me last week in my truck (2000 5.4L 4x4 ORP w/ 46,000 mi)- and it didn't start until I had less than half a tank of gas - using the heater also seemed to get it started.

Before I got a chance to changethe plugs, I needed gas. I filled it up w/ premium and put some fuel injector cleaner/gas line cleaner in it, and the probelm went away. I went ahead and changed the fuel filter this weekend anyway.

I still don't get what the heater had to do w/ it, coincidence?

 

Hmmmmmm? Maybe we all have similar problems with different fixes. Anyway...I changed the fuel filter today, then drove it 10 miles, and it seems to be OK. I could see some rust particles, (or something solid) coming from the inlet side of the old filter when I drained it. So there was definately something in there...good to see the filter was doing its job. Lord knows what you get in your gas these days.

Thanks for the help!
MR

 

Gawd i wish i could fix mine that easy! I've tried everything i could think of,filter ,pump in the tank,on the frame,coil,mag. pick up,eng.module,throttle postion senor,reset the fuel relay! I'm at my wits end running out of ideas and CASH! Truck is a 85 f150 5.0 FI. Someone please!! Runs fine then starts bucking like crazy!

 

BTT!!

 

Green,
do a compression check on the cylinders, check hte plugs for evidence of leaking coolant, and coolant in the oil - sounds like you could have a warped/cracked head.

 

The truck runs fine until it warms up a little, then it bucks like crazy like it's out of gas,do you think it might be something electrical,cause i can rev the heck out of it and it sounds fine,also i can give it a little throttle,and move it across the level then leave it cool down a little, it does the same thing seems like somethings breaking down,i'll try what you said.Thanks for answering! Another thing i forgot to mention,a friend of mine did a test on it, and it kept saying,not enough current to the throttle postion sensor,what's that mean?

 

Don't know what that means...
I had an Escort GT that developed similiar symptoms, only started missing after it warmed up, and then it bucked like crazy - turned out it had a warped head because an electircal relay went out in the cooling system and had caused it to overheat, resulting in the warped head.

 

green, TPS? I thought the '85 had a carb and the TPS is found only on injected engines? I always thought 5.0 engine got FI in '87.

Can you verify what kind of fuel system you have?

I was going to say it's your coil, since the problem starts up when the engine gets hot, but you posted that you already changed it.

Just thought of something. Does your truck have the electronics box mounted in the engine compartment on the driver's side fender liner? If so, next time the engine starts acting up, try cooling off that box, should be aluminum, with some water. Don't get any on the wires or near where the wires go into the box, just to be safe.

Had an '87 that needed a new box. It would act up when it got hot under the hood.

 

No man it's fuel injected,someone told me it was the first year for FI,on 4wd it's a late 85. Don't know about the eletronics box, my inner fender is plastic. I think it's called MPI? Man when it comes to this electronic stuff i'm lossed,that's why i came here you guys know your stuff! I'll check on that box. Thanks!!