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2007 Grand Prix Tach Runs High, Engine Heat High

The car runs fine for several miles/minutes, suddenly the tach starts to climb, up a jump, then up again. This is when the engine starts to run really rough and I pull off the road, let the car cool down and make it the rest of the way to work (about 15 miles).

Here is what I have done: Radiator flush and fill; Oil and filter change; Cleaned EGR and replaced gasket; put in new spark plugs; changed the transmission filter and oil; replaced the O2 upstream and downstream sensors; replaced the thermostat 195 to 180; replace the coolant temp sensor.

The check engine light does not come on (except on start-up check sequence), so it is working. Their are no trouble codes (other than when I removed the downstream O2 sensor to check if I would get errors). The cat converter doesn’t glow at night, and doesn’t rattle when tapped. The resonator in the exhaust does make a rattling sound, but I don’t see why that would be the problem.

I am at my wits end. Does anybody have any clue what I should try next? The water pump isn’t leaking. HELP, HELP – please!

You say the tach jumps, but does the engine rev up with it? Of not, you may have a malfunctioning camshaft position sensor or crankshaft poistion sensor that is throwing off the ignition timing and causing all these issues. I had a job once with a damaged encoder for a crankshaft sensor that causes all kinds of problems like this.

Thanks BustedKnuckles, sounds like your on the right track because no, the engine in fact feels like it has lost power not revving up with the tach. Just to clarify, however, are you referring to the magnetic resistance sensor behind the harmonic balancer? That would require a case learn to be done, and I don’t have the equipment.

Does your car have an engine coolant temperature guage on the dashboard? What does it show during this sequence?

@GP07, do you have a shop manual for this car? Even a Haynes or a Chiltons manual should be able to locate the crank position sensor. But, the sensor may be good. Check the encoder for damage. Also check the sensor for gunk or debris. Anything around that may be throwing the sensor signal off. That way, you don’t need to resync a new sensor.