shaking in overdrive

[95dime]

car is a 95 gp 3100 with automatiuc trans. very smooth till it shifts into overdrive and then it shakes/vibrates. let off itll drop to neutral and it stops....or if i put it to the floor it shifts back down and stops but soon as it hits overdrive it shakes again. i figure im gonna need a transmission soon but any idea what it is or how big of a job itd be fixing it? thanks...

[bszopi]

When mine started doing that, it was a coil pack going bad, causing only 4 cylinders to fire at lower RPMs. I had to drive an hour or so home like that, and just kept it in D vs OD and it was fine.

[1994KlrWhaleOlds]

To me, it sounds like the Torque converter lock up solenoid is going or has gone bad. Does it go away if you step on the brake as you're driving?

My van had that problem when I bought it, they had tried EVERYTHING else to fix it. I changed the trans fluid and filter and it fixed it, apparently.

[95dime]

^^^how would you tell if a coil pack is going bad?

[gpse3400]

Yeah you may have an ignition problem. When lock up occurs the engine has a direct link with the drive wheels like a manual transmission. Any improper engine performance will be known.

A bad coil pack or ignition modual will cause a misfire, amoungst other things that may happen due to ignition malfunction. May also be a fuel problem too.. Basically if your engine isn't running smooth, that roughness will become amplified in lock up.

So the question to you is is your engine even running correctly?

[95dime]

it idles smooth at 1000rpm when in park, drops to about 900 when in gear but brake is on, it seems a little rougher almost like it has a cam but i talked to the previous owners brother who is a friend and he said it was always like that. acceleration is smooth but then when i hit overdrive it shakes and is real rough.

[gpse3400]

3100s run very smooth. I think you have a misfire. I would isolate it by pulling plug wires while the engine is running and check for a reaction. The plug wire you pull that doesn't cause the engine to react is the dead cylinder. Be careful of the rotating belt drive and not to tear up the plug wires.

[sharkey]

i deal with this exact problem all the time at work. the tranny is actualy going into lockup, not 4th gear. when it goes into lockup the transmission is directly coupled to the tranny, and it will load the motor up. what you are feeling is an engine miss, it is not a tranny problem and dont listen to anyone who tells you it is.

[GutlessSupreme]

I'll add misfire; my Cutlass used to stutter under load in OD, lot of work being done that the lower RPMs. I thought it was a TCC problem, turned out to be one of the coilpacks.

[gpse3400]

I'll add misfire; my Cutlass used to stutter under load in OD, lot of work being done that the lower RPMs. I thought it was a TCC problem, turned out to be one of the coilpacks.

We've met before havent we???

[GutlessSupreme]

Like actually met? or just in another topic?

[gpse3400]

Yeah I thnk we met a number of times! The first time I took some parts from a wrecked turbo GP that you had in storage! I Needed that hood because my atlernator busted a hole in mine LOL. And then there was that car meet at URI, and then I bought my buddy over and he started to takes some parts from that car!

[95dime]

alright, i replaced all 3 coilpacks and also put new bosche wires and ngk plugs. its still shaking. what else could it be? i have a plug that i cant find anything it goes to near the alt. its a 2 wire with a red plug. theres anotherone that looks just like one that i have plugged into a square black box behind the icm. could the icm board itself be going?

edit: info on the car- 1995 grand prix 3100 sfi auto. has 2000 malibu3100 heads and roller rockers. other then that its all factory. has 100k on it.

[gpse3400]

I think its the ignition modual..

[GutlessSupreme]

Yeah I thnk we met a number of times! The first time I took some parts from a wrecked turbo GP that you had in storage! I Needed that hood because my atlernator busted a hole in mine LOL. And then there was that car meet at URI, and then I bought my buddy over and he started to takes some parts from that car!

OH! no that was Greg (no1kicker), I bought my TSTE from him. I was at that URI meet though, back in April '04 I think. But I left early for work, I know a couple of people showed up after I left. But yea, Greg had a parts TGP a couple of years ago, must've been him. I had a TGP for a little while, but I only had the Cutlass back then.

sorry for thread hijack