What are some possible problems that could be poor gas milage and a rough driving truck, it's a 98 sc 4x4 4.6 with 60k the idle seems fine but driving it seems to have a shudder which gets worse at higher speeds. any help is greatly appreciated.

thanks Mark

 

Mark, i have the same truck and miles.

With the help of this board, my truck runs great now.

My truck felt sluggish, 12-13 mpg.

On the way to work one morning it started shaking, got worse, engine light started flashing, then it would stay on all the time, flash when i was accelerating.

Bad spark plug wires. Changed the plugs and wires, ran fine, back to it's normal sluggishness, but with a little more response and pep. Mileage 12-13 mpg. I bought NAPA lifetime wires. (Belden $62). The way they are designed, the heat gets to the boots, and they pop off the plugs. I'm sure i'll need new ones before 100k, so only buy them once. For now, push all the plug wires down onto the plugs. One may move down a little, that would be the troublemaker. If one is bad, they all are.

I just did an intake/injector cleaning Friday. I poured a bottle of BG injection cleaner 44k in the tank, a small bottle of BG spray for the intake, some cheap NAPA carb cleaner for the throttle body and a new air filter. Drove it 250 miles today, and WOW. Like a new truck!

It used to bog after gear shifts, not any more, it digs and goes!

If i did it again, i'd clean the intake/injectors before i changed the plugs. I did'nt have a choice.

I did a snap shot of my milege today after 250 miles and it was 15.5 on a good city/highway mix.

Cost: about $110 for everything.