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4T65E-HD What it did before it went

BigTom73

BigTom73

New member
Maybe this will help someone. I have a 97 GTP with 180K miles on it. I just purchased the car not too long ago. I know the supercharger on it came from a junkyard and the current torque converter is brand new, and that is about it.

The car was running fine until I downshifted to pass a semi on the highway. When it shifted back into overdrive is when the problem started. It felt like a tranny shudder to me.

I asked my personal pontiac mechanic what the problem could be and he said that the trannys will shift funny if there is an engine miss. Hooked up the scantron to the OBD-II port and behold - multiple cylinder misfires.

Next step. Three new coils. New wires and plugs. And, the miss was still there. The next thought was bad gas ( I didn't think so, but I had to indulge my personal mechanic.) So I put 93 octane in with injector cleaner and octane booster and took the car for a nice long ride. That was saturday night. Sunday morning - no transmission.

When its cold it will move a little, but once it warms up there are no gears. I have a junkyard tranny to put in it and that's where I'm at.

I hope this might help anyone who needs it. Good Luck.
 


pump shaft could cause what you are describing but i doubt thats it. most likely is a pressure concern though

if the forward band broke you should still have reverse. no input clutch could cause this too i suppose
 
Did your misfires stay on the same cylinders through changing out all you have? If so have what codes other than the misfires is it throwing?
 
First to clarify. I didn't downshift it manually, the detent cable did all the work.

The misfires where on random cylinders with no codes showing. The only way I could confirm the misfires was using the scantron tool. Someone else drove while I was looking through the engine data. Misfires came up in pretty much all cylinders before and after I changed the coils and wires. All other engine data was normal.
 


missing could be the switch on the tranny where the shift cable goes on, i had a bad missing problem when i got mine and that was all it was, also check the pcm wires in the airbox, mine got all chewed up and caused problems until one day i decided to look in there
 
Just an update.

The new transmission is in and the miss is gone. The car runs better than ever and the MPG's went up. I'm not sure if that is from the tranny or the new coils / plugs / wires I tried.

Hope this helps.
 
Same thing happened to me & the exact same year & miles too. My car seemed like it was throwing random misfires & then 2 week later the TC & trans shutdown & I lost all access to gears. I just put a new tranny in & just like you said, misfire gone & my MPGs shot up big time
 
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