I was reading a post I did about 4 years ago which is related to what is going on now. At that time, I used to tach 1750 at 55 mph then it gradually went to 2000 rpms at 55 mph. Now at 55 mph, I tach at 3000! Can a sensor or switch go bad without the ECM throwing a code? I have replaced the IAC,TPS,MAP,ECM. The only things I have'nt replaced is the knock and vss sensors. I went down the road and the tranny shifts smooth and soft with no downshifting on its own and no hard knocks. Cat clogged and or tcc maybe? Its getting very annoying?ANY HELP!!!

Ken

 

its definately not related to the engine. dont go throwing money into it for sensors hoping to solve the problem, your just wasting cash.

This is a TC or trans problem.

First off, check to make sure the TCC is functioning. It could be slipping and not actually locking up tc fully.

Next i would be looking at the tranny, making sure its shifting into 4th and not slipping. Check ATF smell and level.

 

your tach is most likely going bad it is a common problem. there is a circuit board int eh gauge cluster (i believe) that has a bad capacitor, that causes the tach to read higehr than it should. and the vss only tells you speed. and the tcc being bad would only alter your rpms by around 300 rpm. to check the locking of the torque converter, get to highway speed and in 4th gear and lightly tap the brake and watch the tach it should read higher for a split second.

 

sorry, i did assume he uses an aftermarket tach. Pretty much every 3rd gen i have seen has an aftermarket tach because the stock ones are so bad!

Are you using a stock or aftermarket tach?

 

I got a stock tach. In fact, I replaced the cluster from a V8 and took out the chip in my V6 cluster and put in the V8 cluster. It was doing this before I changed anything though. I have driven down the road and wait til it shifted for the last time and hit the brake pedal just enough for the light to come on and the tach went up a couple 100 rpms. But the tcc may not be engaging all the way and locking up. If I had a scanner to put in the ALDL connector while I was driving to see how many rpms I'm doing as compared to the tach.

Ken