I have a quick question I hope...What is the problem when the truck only shutters or shakes over 30 mph and ONLY does it under throtle...as soon as you let up on the gas and coast it stops? Thanks

 

Could be a lot of things.. but I'd start with the drivetrain... see if your U-joints have extra play.

If you keep increasing your speed, does it go away?

 

no..doesn't get better or worse..but completly stops as soon as you lift the gas

 

s-h-u-d-d-e-r

I had to, sorry.

 

I agree, could be a lot of things. Hard to tell without being there, but a place to start. Check AFM, TPS for fluctuating or dead readings with meter would be a place to start. Either of these could cause a fuel stutter due to ECM reaction to bad readings.

Just a few suggestions above, post what you find after testing.

 

Bad front end components, tire rods, ball joints, etc.

Shocks

Tires and rims arent true (round)

I would start by having the tires balanced at a place with a dynamic balancer, a hunter 9000 iirc.

 

Auto or 5spd?

4wd?

Any recent mods? (lift, tires, etc...)

Been driving in mud at all?

 

since it quits this after you let off the throttle, it is probly engine related.

perhaps the fuel filter is clogged.

perhaps the plug wires are worn or they are arcing out onto ground

 

I disagree with engine issues; I think it's drivetrain, probably u-joints or suspension components. It will be interesting to see who's right!

 

i vote fuel issue. tps adjustment took care of my similar problem. anything above 30 mph if i just lightly pressed my pedal my truck would buck.

 

i say that only cause his problem changes when the engine is unloaded.

 

ok thanks for the help...I found out one cylinder is low on compression about 90...could this be it? It doesn't feel suspension or tire related.

 

also it doesn't buck like a fuel issue...it just vibrates even with a smallest amount of throttle...let off and it stops instantly

 

Well, that compression reading is a problem.

I was guessing u-joint, when under load, was binding. Still might be true but you have a known problem now with your compression reading. Fix that first.

 

ok, so what do i win?

 

im gonna put a vote in with it being the differential..

 

if you can, put the truck up on sturdy jackstands, start the engine, let it run, put it in gear, and see if you can pinpoint the noise.

Be sure it's steady, cause if it falls, then it's going right through your garage wall.

 

I vote for it just being a POS. Only 90 psi is a major problem. Time to rebuild. I wouldn't sweat any u-joint or sensor issues until you take care of the compression issue.

 

Actually, try putting a little oil in the cylinder and see if the pressure comes up to where it should be.

 

to continue his post, if the pressure does rise, then the rings are more than likely shot, if it doesn't, then valves/headgasket are to blame.

If your compression gauge can plug into your air compressor, then remove the oil filler cap, and the radiator cap, then rotate the engine to BDC for that cylinder, and pressurize the cylinder. Then, listen for air escaping, and look for bubbles.

Coolant = head gasket
Oil = rings
exhaust = exhaust valve
intake = intake valve