OT, '97 4L80 trannie - convertor lock up issue.

Dave from MN · Jun 2, 2009

Need some help here. I have my 1 ton in a reputable transmission shop and he has rebuilt the trannie. some recall my 2nd rebuild, leaking tranny cooler issues from a few months ago. Well, the the tech said that the tranny is done and done right, BUT something is still wrong because the cobnvertor doesnt lock up until about 65 mph, and should be doing it between 40-50. He says driving it like this will burn up the new transmission very fast. He has never had this issue and thought that it was somewthing the GM shop could program back, GM shop told him no it is set in the computer, there is no access to change it. Does any one have any idea what he could check. He does an awful lot of these same trannies and says this one has him stumped. Is there a sensor somewhere? Possibly a brake pedal sensor, abs, speed sensor. Lot of knowledge on here and I am hoping some one can help me out.

twopop · Jun 2, 2009

dont know much about them,however,put a code reader on it and see what it says.not all codes turn on check engine light.you do have a speed sensor on the back of the tranny.and the brake pedal turns off the convertor when you step on the brake,but if is going in at 65 i doubt its the problem.could be speed sensor even 02 sensor

Allan in NE · Jun 2, 2009

Assume the truck hasn't been chipped?
Assume it has the correct sized tires?
Assume no warning lights coming on or codes set?

Converter is locking, but just locking late? Everything must be working okay.

I know I sound like a broken record, but check that darned fuel filter because if plugged, it will play havoc with the TPS parameter on GM trucks.

Allan

Anonymous-0 · Jun 2, 2009

Good advice on fuel filter, it happened to me.

Brian Jasper co. Ia · Jun 2, 2009

If the vehicle speed sensor were faulty, it would not shift out of 1st. Does the engine run well? Air filter restricted? Fuel filter restricted? A poorly performing engine will have late shifts and late TCC. The TCC coming in is directly related to engine load and is controlled by the PCM. He is right about no TCC overheating the trans. If you must drive it, don't use overdrive. Poor engine performance will heat the trans up too.
Having the latest programming downloaded from GM might help shift quality, but I doubt that is your concern. When the guy put the new trans in he should have cleared the TAPS. Not clearing the TAPS can make a new trans shift really erratic.

Dave from MN · Jun 3, 2009

Engine seems to have a miss, in my opinion seems to run rich. Catalytic convertors were "gutted" prior to my owning. Fuel pressure regulator was replaced a while back and I am assuming they did the filter at that time. What is PCM and TAPS? GM dealer is saying i need a new computer, well that is what they are telling the tranny shop. I beleive them are pretty pricey.

redblood · Jun 3, 2009

Our 98 k2500 454 with a 4l80e trans was sent to the dealer for software updates , for the new computer - ecm - pcm, when it came back it does the same thing. That was 20,000 miles ago.

At the time I questioned the dealer they said it was because originally the trans shifted into OD too late and would overheat the trans on the road when pulling light loads , up to 1.5 tons. So GM ,in all thier wisdom, changed the calibration.

It's not the lock up that is not working it is 4th gear that doesn't engage until high speed.

By the way say good bye to decent fuel economy.

Joe

OT, '97 4L80 trannie - convertor lock up issue.

Dave from MN

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twopop

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Allan in NE

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Anonymous-0

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Brian Jasper co. Ia

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Dave from MN

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redblood

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