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· Premium Member
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Free reving an engine that high is not good. All engines perform best under the proper load. Free reving will damage and can even blow an engine. When I am running tests on engines for what ever reason I do not go beyound 2.5K rpm, there is no need for it. Wheither I am heating the engine up to test the cooling system, charge the AC, check the alternator, looking for any leaks, etc., I keep the engine at and below 2.5K rpm's and I do not run it very long at that rpm either. Many "dirty" mechanics will rev your engine up to the rev limiter just to say you need a new fuel filter/pump, which all they are trying to do is rip the owner of the car off.:mad:

Many of todays PCM/ECM's are getting smarter programing and can control/talk to the transmission control box. These newer systems can detect when the engine is under load and when it is not. Many even control the AC so that when you climb a steep hill or do a power take-off that it will disengage the AC to add HP to your drive wheels.

Since your engine ONLY stumbles when free reving, and not driving, it appears your PCM is taking charge and not allowing the engine to be destroyed.
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