RPMs Jump and Hesitant Gear Changes But No Codes

Complete Transmission Repair Cost Guide Transmission Forum – Ask an Expert Chevrolet RPMs Jump and Hesitant Gear Changes But No Codes

This topic contains 1 reply, has 2 voices, and was last updated by  mstern001 2 months, 2 weeks ago.

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  • #9887

    Admin
    Keymaster

    99 chevy trailblazer 120k… first gear and reverse fine. pulling from stop signs and moving automatic to 2nd she chugs, push gas more, to 3rd (at 35mps) runs fine. Manually placing this 4spd into 2nd at stop signs and moving it to 3rd at 35mph = no problems. I can manually tell the tranny I want 2nd and I have no problems.

    Driving at cruising speed 55-70 with cruise or no cruise, RPM jumps 200 and settles back down. does this intermittently for no rhythm or reason.

    NO codes on console or scanned, NO codes on transmission from shop as when I take it in it was not acting up that day. It chooses when and everytime I take it somewhere she acts just fine. (I know right!!) Tranny guy said, “when i was driving it, it did not blow a code, its not acting up so therefore with GM products it needs to be acting up to read a code).

    I heard everything from distributor, vacuum leak, plugs….I have changed the TPS, cleaned MAF with proper cleaner, tranny filter change. Quoted $ 1600 for rebuild, (not sure if this is complete rebuild or some off the wall parts inside) oddly they quoted this as a “no matter what” so not sure if this is what they find wrong or complete more questions need to be asked I am thinking. 1 year 12k warranty.

    Two questions for you friend, I need lots of front end work, could this effect the tranny (vss??? at the tires ect??? causing the slip {if this is indeed what they would call slipping as I have no idea what that terminology means}) and second, What if any thoughts can you throw at me….

    I do thank you for writing this up, it was very informative. I hope if you answer, I get a bump in my email saying this sight posted a reply, so i can return and read any words of wisdom you may have posted. Thanks again

    #9892

    mstern001
    Keymaster

    Hey, thanks for the kind words. I always enjoy hearing from you guys and I have tried to help readers out for a very long time. I remember one GM products that … well, I can’t really go into it but suffice to say it was a positive result.

    With that said, I think you’ve done a great job of troubleshooting the issue and I think you have hit the nail squarely on the head. From the sound of your issue, your transmission is working — you have to use manual shifting, but it goes into the gear you select and moves along in that gear quite nicely.

    Now, it is true that there are a number of conditions that could mimic the problems you have outlined, but, here’s the thing of it, they would generate a code and it would be captured by the Engine Control Module (ECM). And, since you are not getting any codes generated, I believe that the problem is purely mechanical and outside the transmission.

    It is also possible that the tire/wheels have a problem. If one of the corners of the SUV breaks then essentially you are asking three wheels to do the work of four. Now if this were possible, your vehicle would just pivot around the bad wheel in a big circle. So, if you have a combination of VSS failure and the failure of a tire/wheel on one of the corners, then you have a condition that could easily cause your vehicle to surge.

    Hold on, though, this brings up another group of possible causes, electronic. Though you have touched on it fairly well in your question, I will expand on it to say that if one of the wheel sensors or a sensor on the crankshaft has gone or is sending back faulty information to the ECM — also the chief computer in the engine bay — it is easily possible that the combination of the bad sensor and the ECM misreading the information, is causing your SUVs transmission slipping. The reason there is no code being generated is simply that the ECM isn’t reading it as an error so there’s nothing reported or stored.

    Let me know what happens.

    You asked me two specific questions and I have to tell you that if your VSS (Vehicle Stability System) is gone or going your vehicle will act much in the manner you describe — surging and the like as the VSS tries to right things, causing the crankshaft to turn at unacceptable rates.

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