ptcfast2 Posted June 6, 2011 Report Share Posted June 6, 2011 (edited) Alright, so I'm having a slightly alarming issue with my 98 3.1 Lumina w/ a 4T60-E. Here's what I've got: When I brake and the transmission downshifts I get a slight or severe RPM drop at each downshift. The RPM drop is quite severe. You can see the tachometer dip lower and lower (3rd --> 2nd is better and 2nd --> 1st is the worst), before bouncing back to the normal RPM range for that speed/gear. Oh, and the transmission upshifts firmly/normally and downshifts firmly during all of this; Had it rebuilt about 6,000 miles ago. When the 2nd --> 1st downshift hits it's almost enough to stall the car, bringing the engine below 500RPM. When the car hits the RPM range the lights dim dims, the blower botor slows down/air stops coming out for a moment, and the brakes act a bit qwirky. The car has stalled twice since this started to happen - low speeds luckily... I know for a fact that the problem is worse when the car warms up. I've double checked all the vacuum hoses, connectors, replaced all valves, transmission modulator, etc... basically anything I could think of that would possibly cause the problem. Does ANYONE have any possible idea/reason as to why this might be happening? It's driving me crazy and worrying me. Edited June 6, 2011 by ptcfast2 Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted June 6, 2011 Report Share Posted June 6, 2011 RPM drops during downshift? should stay relatively the same if not bump up a little for a moment. Quote Link to comment Share on other sites More sharing options...
mpesh Posted June 6, 2011 Report Share Posted June 6, 2011 check your MAP Quote Link to comment Share on other sites More sharing options...
ptcfast2 Posted June 6, 2011 Author Report Share Posted June 6, 2011 (edited) RPM drops during downshift? should stay relatively the same if not bump up a little for a moment. Yeah which is why it's worrying me. It will actually dip below what it should stay at during the shift and then bounce back to it. I worded it wrong in the original post . check your MAP MAP is actually brand new (along with every sensor on the engine - installed it about 2,000 miles ago with 0 miles on it - new GM crate engine). The old engine would have the tach bounce down a bit as well, but it didn't act like this - it's more noticeable now and seems to have just gotten worse. Edited June 6, 2011 by ptcfast2 Quote Link to comment Share on other sites More sharing options...
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