I should state first off that I'm not much of a car guy when it comes to the actual mechanics behind them. I just wanted to check if there's anything going wrong with my transmission.

I drive a 03 GMC Envoy(Equivalent of a trailblazer) with a Vortec 4200 4.2l Inline 6. I just had my transmission fluid(100% flush) and filter changed.

When I press the pedal down about 75%, the tachometer rises quite a bit and suddenly I get a ton of acceleration out of nowhere and the RPMs jump really high,almost like a turbo kicking in. (Shifts at 6k, redline is 6300rpm) It does not feel like it's shifting. I should also mention that my engine is naturally aspirated, and there's no modifications.

I'll be at 3100RPM then it'll suddenly jump to 5500 in rapid acceleration.

I don't know if it's from the electronic fuel injection system or something, but it just seems weird to me. I've never heard of cars doing this.

Is this natural? If not, what are some problems I should look for?

5 Answers 5


Your torque convertor has a convertor lock-up clutch. When reaching a nominal speed and engine RPM the convertor comes on and locks the convertor forming a slip free drive. When you use kick-down or near full throttle acceleration, the convertor clutch unlocks. This allows the stator in the convertor to allow torque multiplication and give the vehicle its fullest acceleration. It also allows a difference in rotational speed of the impeller and turbine - convertor slip. This is the RPM increase you see on the rev-counter and is what happens in normal operation.

If this happens at low speeds, you should allow the repairer you used to check the vehicle, if only to re-assure yourself.

  • This is probably the most likely answer, because they said no metal shavings were found in the transmission fluid or filter. It also doesn't feel like a slip of power, it feels like a ton of power suddenly kicking in.
    – Alec
    Commented Dec 14, 2013 at 0:18

Sounds like the transmission is slipping. Check the fluid level, it that's correct take it back to the shop that just serviced the transmission.


Id say something is wrong with the transmission from the fluid flush, it is not the easiest thing to flush transmission fluid, and in doing so with certain transmissions you can actually do more damage than good if not done right.

What it sounds like is its not in the correct gear and shifting at the incorrect points, this would be caused by many things but most likely I would say it needs a trans rebuild of some kind.

If it worked fine before the flush and now this is a new problem, I would take it back to the shop that did the flush.'

Also if I may ask, what was the reason for doing the trans flush?


Need to replace solenoid switch, which is on Top of the Transmission Power Supply box. The solenoid switch didn't hold power supply properly. I had this problem for a year like this my Dodge Caravan Minivan which has 178,000 Mile on it RPM 4800 when speed 70 MPH. A Mechanic was telling me need to replace the transmission, which is $1800.

As soon i replaced solenoid the issue was resolved and now the RPM's are about 2000 at 70MPH.

Switch Cost was $289 include parts and Labor.


I have the same problem my house mechanic told me that some of my the electrical parts had some water in it so he dry it up so my rpm was fine and the car not jerking plus my oil indicator light is not going on as it was before

I have the Golf 3 GSX

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