RPM governor

Asked by WillyLL Mar 15, 2018 at 10:31 AM about the 2003 Chevrolet S-10 LS ZR2 Extended Cab 4WD

Question type: General

My 2003 Chevy S10 ZR2 has some kind of rpm controller programed in. At low speeds while descending down a steep grade, especially in low range, the engine compression will slow me down to lets say 10 mph. Then suddenly it revs up and I will speed up to lets say 20mph. So I have to brake. Then suddenly the engine  compression kicks in again, I let off the brake, the rpms drop and I slow back to 10 mph. Then it all starts over again. Is there a way to disable or deprogram this feature? Thanks

3 Answers
103,435

KenF answered 6 years ago

The PCM is the REV limiter. You would need to swap to an aftermarket PCM and tune it to eliminate a REV limiter. It's designed that way to protect engine from excessive RPMs. Stock PCM can only take factory presets. I don't think your symptoms are related to the PCM. Maybe transmission or clutch related.

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WillyLL answered 6 years ago

It's not trying ti limit high RPM. It's like it's trying to prevent too low of RPM. Someone once said it was a feature to prevent the engine from stalling from too low of RPM. It is more pronounced with the AC on. It wants to keep the RPM up over 1000. By the way I forgot to mention that my S10 is a manual transmission.

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103,435

KenF answered 6 years ago

I see what you are saying. Engine braking downhill and engine occasionally revs too high forcing you to use brakes to slow down. I don't know what shape your engine, transmission or clutch are in so can't comment on those, but one potential factor causing a spike in engine RPM is a vacuum draw, the engine is attempting to provide vacuum for something and has to boost RPM to make it. Or conversely a vacuum leak is allowing unmetered air into intake during engine breaking and PCM increases fuel to compensate. The increase in manifold vacuum (first due to engine braking and then possible leak) may be causing the engine to surge. Try going through the intake systems, clean everything and look for any vacuum leaks. Everything is suspect, PCV, EGR, all hoses.

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