12point

Hey guys, lately my truck has started bucking while I am driving down the highway. This doesn't happen when I'm cruising at normal speed but when I come to a hill and give it just a little more throttle to maintain speed it bucks... if I push the throttle down just a little bit more and it drops a gear it's fine too. It's just at that one point that it begins to buck and otherwise it's fine. No check engine light or codes showing up and no problem driving in the city either.... does anyone know what the problem might be?

screamineagle

A coil on its way out most likely. They dont always throw a cel.

12point

Any idea how to figure out which one needs replacing the most? Or am I just better off doing them all..

coborn35

I'm in the same boat as you. Two coils right?

techrep

iTrader: (1)

Mileage ?
last plug change ?
Check FPDM ?

12point

Truck is an 08' fx4 with 130k on it. I have never changed the plugs since I have owned it but I've only had it since October. Not sure what FPDM is?

techrep

iTrader: (1)

I would start with a plug change, could very well be your problem. The Fuel Pump Driver Module (FPDM) is located under your spare tire mounted to the frame rail..it gets corroded and cracks in half to expose the circuit board.

12point

However as far as the coils go, what's the best way to determine if the coils are good or bad?

corey_lax

You'll need it to throw a code so that you know which cylinder is misfiring. Then you can swap that coil to another cylinder, and see if the code follows the coil, or if it is plugs.