Poor transmission lockup

[robbie_NH]

A year ago I had my 96 Roadmaster sedan reprogrammed for the Chug-A-Lug engine surging (it was never done by previous owner). That seemed to work fine until two months ago. Now it seems the torque converter lockup happens abruptly at exactly 60mph on occasion. So I had the tranny rebuilt by a local guy that came highly recommended. It still does the abrupt and "late" lockup and now I notice it searches for lockup going up small inclines at about 65mph. I took it back to him. He's had it now for 2 weeks and according to his research, GM has it programmed to lockup between 60 and 70. Strangely, it locks up at 45mph in 3rd gear. This seems really silly because the lockup is supposed to save gas. I don't know if this speed for lockup was changed in the new program of a year ago. Has anyone else had this sort of trouble with their transmission?

[maxwedge]

The progrqamming can cause this, so can an engine out of tune, a bad tps is another possibility, this isn't always a trans issue. A full scan should be done to lookintg at all the sensor inputs then a trans scan to look at when tcc is commanded. Is it 4 th that waits till 60? If it locks in at 45 what is happening at 60, not the tcc, must be 4th, no?

[robbie_NH]

Running in 3rd gear the torque converter (TC) lockup occurs about 40 mph. When in OD it occurs at 60 mph or above. In OD the lockup sometimes gives a jerk plus it now seems to hunt at around 60 mph.

The shop ran the diagnostic tool while they took it out driving to witness the above operation. They tell me that the lockup is a gradual engagement, that the solenoid is pulsed (PWM) over about a 10mph range until it's fully engaged.

I just picked the car up and was handed this ATRA Tech Bulletin #1026 relating to the 4L60E and 4L80E transmissions dated August 2006 titled: No TCC apply, TCC apply not commanded. It reads as follows: "Also some GM trucks will not command TCC apply until vehicle speed exceeds 65 - 70 mph. This has been observed on otherwise normally functioning vehicles with no DTC's pending or present.". The shop says that the RM also uses the 4L60E transmission.

When I first bought it in there was a misfire code in the RM's computer. The code was removed and did not return while the transmission continued to engage lockup at > 60mph after being driven extensively.

I will say that while driving the car home at between 35 - 50 mph for about 15 miles, I could feel a roughness in the engine. I think I'll take the car down to a Buick dealer and have them look at the engine (with your suggestions), because at this point, the transmission was rebuilt but the initial problem with it remains. The rebuild included replacing the TC, solenoid valves, transmission ground wire (sometimes a cause of erratic operation), rebored TC solenoid valve body and new valve - anything and everything that could have been the problem.

Rob.

[maxwedge]

That hunting may be caused by or the result of low engine performance which causes a slightly greater throttle opening, which translates to later shifting.