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Discussion Starter · #1 ·
My wife was complaining that her 96 Jimmy was surging at about 45-50 mph. When I drove it, it seemed to be more of a case of the trans shifting up and down from 3-4. (Or maybe the converter locking and unlocking?) This is a new phnenomenum(sp) and is getting worse. Anyone have this happen on a 4L60 before?
 

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I'm not certain but I think that is the area that it shifts into overdrive. And you may be noticing it more since you are looking for it. Our '96 Blazer was the same way. I found that anytime I was driving and not on the highway I left it in drive and not OD. Also you will find to that in town when in D that it will not coast as fast as when in OD. It made it better when following others that you did not have to hit the brake so often to slow up. Give it a try. If you do drive in OD all the time it will be strange when you go to put it in reverse as the natural reaction of doing it will now be one notch off.

Kevin
 

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how many miles on the tranny?

what engine?

4x4 or 2wd?

I sound like stu.... :thumbup:

a 1996 unit will be a PWM lockup system on the converter... these can start acting up from valve bore wear of the PWM system .

If driven long enough with a converter lock up problem usually the MIL will light up with a P1870 code

could be a shift solenoid problem

drive down the road on a long section..... get the vehicle to perform the problem... lightly step on the brake to cancel lock up to see if it is the converter lock up function causing the symptoms
 

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Discussion Starter · #5 ·
It has about 129,000 on the clock,4.3 liter, and is a 4X4. Has been well maintained and the 4X4 function is mostly just for snow storms.
The P1870 code....is that read by an OBD scanner? I will try the light brake application while it's doing it tomorrow and see if that makes a difference. Just curious....if it's a PWM problem from valve bore wear, how complex is the fix? Thanks for the input , will let you know how it reacts.
 

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Discussion Starter · #6 ·
Took it out today, and it seems to be convertor lockup. When I cruise at 43-48 mph, it can't seem to make up its mind whether to lockup or not. At higher speeds it doesn't behave that way. If I touch the brakes, it stops fluctuating...I can duplicate the behavior at higher speeds by intermitantly touching the brakes.
It seems like whatever signal is sent to lock the convertor up is inconsistant at the 43-48 mph range.
 

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My 200R4 "hunts" occasionally. Since it's operating with a TCI conversion rather than the computer, I just shut the lock-up off.
 

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Discussion Starter · #11 ·
Yeah, she made it back, been kinda busy lately. She said it was doing it in Drive too....but you know how women are when it comes to cars. I drove it again yesterday and I'm sure it is the converter lockup, not the OD. The service light came on also. Gonna get it scanned as soon as I've got some time. Appears I might have to put a rebuilt valvebody in it, to the tune of $225.
 
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