QuestionJust recently took a trip about 300 miles interstate. Each time the car reached from about 70 to 85 mph it would periodically start shacking and jolting in the front end. It reminded me as if a governor was shutting off the engine for some reason. The fluid levels were fine and no check engine light came on. It also seemed to be worse when there was a decline or incline in the road. It did the same exact thing with the cruise on or off.
AnswerHi
I would check first all the ignition components (Plugs, wires, check the coil towers [3.1l] or check the coil housing [2.4l].
After these are checked or replaced, I would then have the fuel pressure checkec while running down road and acting up. Fuel pressure should always stay steady.
A tune up may be a good place for you to start Plugs. wires, fuel filter, throttle clean, injector clean. This NEVER hurts no matter what. Use GOOD DELCO Spark plugs.
If all this checks out it COULD be an intermintant Catalytic converter. You can have that checked at a muffler shop, usually a free check.
Auto manufactures (GM I Know for sure) do have a "cut off" speed or "rev Limiter" programmed into the vehicles computer. It is programmed to cut out the engine at the speed rating of the OEM FACTORY INSTALLED TIRES, not replacement tires. I really doubt you hit that at 85, UNLESS you have larger tires/wheels that have thrown off the vehicle speed readings. Plus it would not be an occasional, it would happen at the same speed, every time.
I hope this info is of some help.
Just Advice from experience.
Good Luck
Pawl
