I have a 1989 Commanche. New engine only 5K ago. I have an interesting problem. Engine starts just fine, warms up and runs fine, when I reach approximately 60MPH I start to get an awful vibration in the whole truck, feels like bad Ujoints. If I slowly accelerate past 65 it smooths out at about 70 but at 75 MPH the shuddering starts again, and the tach jumps around, the engine almost dies unless I let off the throttle. I changed Ujoints, ball joints, tires, Coil, and tried two used ignition control modules. I have also swapped in used TPS sensors for testing. Voltage from the alternator seems a little low when I have all the accessories going (lights, blower motor, stereo, etc) the ammeter sits just above the red on the gauge. Could this be a low voltage problem from the alternator? I have not replaced the cam or crank sensors, but my understanding is they usually cause problems at start up as well. Does anyone have any idea what could cause this condition. My wife is taking my kid on a long trip next week and I have to get this fixed before she goes. thanks in advance. NEW GUY

 

hmmmm, well I doubt it's the alternator.. is the vibration felt in the steering wheel (Does the steering wheel shake when you let off your hands?)

 

No, the steering wheel doesn't move. It feels like driving over rumble strips with all 4 wheels. I have had an alignment, trac bar is new, springs shocks, etc all new. The first time it happened I thought it was the transmission stuttering. When you get over 75 the tach starts going haywire and the motor dies out. This is what leads me to believe it is in the engine or trans somewhere. Thanks again.

 

are any tires out of balance? sounds to me like two problems getting blamed on one fault