Transmission shifting rough, possible ECM issue?

AHARTLEY

MEMBER
1995 OLDSMOBILE 88
3.8L
V6
2WD
AUTOMATIC
166,000 MILES

Could a bad ECM be causing rough shifting?
In an earlier question it was determined that my ECM was most likely bad.
I have engine fans that are acting up, the shifting has gone rough sometimes.
I've replaced the starter which I'd been told could mess up the ECM, someone else was under my car and had sparked the starter trying to put an air conditioning compressor in it.
The car has about 166,600 miles on it, I bought it at 151,000 approximate miles. The fans were fine when I bought it, I let the fuel pump run its course before I start it so I would have heard the fans before.
The car does "thunk" going into gear but not always the same gear or gears and not always the same times.
On a cold start for the first time of the day, when I take off in between first and second shift it makes a sort of scraping or "sweft" sort of sound, after it's warmed up that quits.
I've studied videos on resetting an ECM however I do not know if that's wise to try.

6 Replies

KASEKENNY

MECHANIC
18,907 POSTS

This is unlikely to be the issue. The ECM could cause transmission issues but the sequence of events that you lay out would not cause an issue in the ECM. Just because the starter sparked would not damage the ECM. This just the battery voltage catching ground for a quick second and it would not damage the ECM.

The most likely cause of your issues are fluid related. I would start with check and changing the fluid. Here is a guide that would help with this:

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

If the fluid is okay, then we need to evaluate the other items in this guide that could be the cause however, I would suspect the fluid is the issue as that is the most common cause of these things. Let us know what you find. Thanks

https://www.2carpros.com/articles/automatic-transmission-problems

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Friday, December 18th, 2020 AT 5:58 PM

AHARTLEY

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113 POSTS

I had been told that at the car's mileage, 166,600, that if I changed the fluid/oil at this point and it hadn't been changed before, and the transmission were on it's way out that it could cause it to finish going out faster. Is this true? If changing the fluid will help I want to do that. I bought this car at 151,000 so I do not know if it's been changed before. It would not be a terrible job to do. Thank you very much for your response. :-)

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Friday, December 18th, 2020 AT 8:14 PM

AHARTLEY

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113 POSTS

I was listening to the car as I was driving yesterday and it shifted from 1st to 2nd then thunked.

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Saturday, December 19th, 2020 AT 7:06 PM

KASEKENNY

MECHANIC
18,907 POSTS

This is a myth. Changing the fluid will not cause a transmission to fail when old dirty fluid would not. The only theory that I have heard that makes sense is that the new fluid removes the clutch material that is floating in the fluid and this causes the transmission to fail as it starts to slip. However, even if this is true the clutch material that is floating in the system came off of the clutches so they are already damaged. Which means it is only a matter of time before the transmission begins to slip and then fail.

So it is impossible to say that the new fluid caused the failure because it may have failed at the exact same time or even sooner.

Hopefully this helps. Thanks

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Saturday, December 19th, 2020 AT 7:44 PM

AHARTLEY

MEMBER
113 POSTS

Very helpful. So case being is that if I'm already having problems, and it's just a matter of time anyway, then what would it hurt. It doesn't seem to be slipping yet. I can't change it yet, however when I get paid I most likely will. Thank you. I would guess from this information I need to also begin putting back money for transmission repairs, a transmission, or another car. I will not go into debt. Thank you again.