Diagnostic on 4R70W, torque converter??

[Todd in KS]

A bit of background - I inherited my 99GT in December. At that time it had 15.8K on the clock. I am sure my dad had not driven this car much at all for the last 10yrs (?) and very positive not "in anger". Drove it just a small amount in December, it was not shifting quite right but got better with some driving and throttle excursions. I drove it back from FL to KS in March. Drove fine but still not perfect. I now have 18K on it and the shifting is greatly improved but I am getting a "surging" especially at steady state cruise (70/75MPH). After looking through threads here I am wondering if my converter is going in and out of lock? How would I diagnose this and what could be done about it? Does it need anything as simple as a flush? I am a 3 pedal guy at heart. Thanks for any insight/suggestions.

 

[lwarrior1016]

A bit of background - I inherited my 99GT in December. At that time it had 15.8K on the clock. I am sure my dad had not driven this car much at all for the last 10yrs (?) and very positive not "in anger". Drove it just a small amount in December, it was not shifting quite right but got better with some driving and throttle excursions. I drove it back from FL to KS in March. Drove fine but still not perfect. I now have 18K on it and the shifting is greatly improved but I am getting a "surging" especially at steady state cruise (70/75MPH). After looking through threads here I am wondering if my converter is going in and out of lock? How would I diagnose this and what could be done about it? Does it need anything as simple as a flush? I am a 3 pedal guy at heart. Thanks for any insight/suggestions.

The best thing to do is get a scan tool. Look at live data, torque converter lock up commanded, and torque converter clutch slip rpm.

With lockup commanded, the slip should really really close to zero.

Out of curiosity, did you have the air conditioner on when it was doing this?

 

[Todd in KS]

Yes, the AC was on. But it does it without the AC on too. I will double check that this afternoon.
Would I need a professional level scan tool for that? I have a code reader but I am not sure it has that capability.
Do you have one you recommend?

 

[Todd in KS]

I got a chance to get on the highway and put it on cruise yesterday afternoon (65/70). AC on and off I was not having the issue of course.
Maybe related or maybe not - when I put it in D from P it wants to go.

 

[Connie]

This is Bob, Connie's husband. I used to build a TON of these Tranny's. One thing I would try is drop the Pan, check the Pan for Metal Shavings first, since they will clog the Solenoids. Then Pull and Clean ALL the Solenoids on the Valve Body and spray Carb Cleaner into the Fluid openings, then blow Air Pressure into each Solenoid through those Fluid Openings. They may be partially clogged causing intermediate issues you are bringing out. Be careful not to tear the Valve Body Gaskets. I would have a Gasket Kit on hand either way just in case. If you do see sand like shavings in the Pan, that could mean the Converter is starting to go. But at such low mileage seems unlikely. After being cleaned the Solenoids should make a rattling sound when shaking them around. I hope this will be helpful to you.