I've got a 91 sunbird le 2.0 w/ th125 that I swapped a junkyard engine and trans into about 3k miles ago. It's had this problem since I did the swap and I have some questions about it I haven't found any answers to.

I put a new filter in when I put the trans in and also mobil1 synthetic trans fluid.

I tried to adjust the tv cable, which seemed to make no difference whatsoever and also it did not respond like my manual said it would(click release and it adjusts - this one just would go wherever I put it). so I put it back to where it was. Normally this would worry me, but the th125 is supposed to have a failsafe fixed line pressure if the tv were to fail.

What happens:

The tcc engage (lockup) is somewhat erratic. Usually about 15 minutes into a highway drive it will decide to lockup.

It usually will not lock up if the temp is below a certain amount and usually will lock up over a certain amount.

Occasionally it will lock and unlock back & forth a few times. Occasionally it won't lockup at all. Occasionally it will lockup ok.

Usually when it decides it is going to lock up, it will engage pretty low - 25mph it will lock and will start to make the car feel a little bogged - then you have to step on the gas to make it unlock.

Also the trans seems to shift fine other than this, when lockup is not functioning at all or affecting anything.

Ok on to some questions:

Manual operation - this would be great so it could be on a switch like they do on some manual valvebodies (my mustang is like this). The things I don't know are: how does it determine you are in third (computer or pressure switch?) and what would the consequences be if lockup remained during a downshift to second? is there a simple way around this or would it be ok if you made sure to use it only on the highway when up to speed in third? for a manual valvebody it works because it does no shifting on its own, for an auto one .. not sure what the solution would be

It seems as if the solenoid itself works ...is it simply intermittently working or might it be the computer control?
Could it just be the pressure switch?

Thanks for any help ... I've gotten nowhere on this issue.

• 86 Skyhawk wagon : 2.0SOHC swap, Megasquirt, 20SEH cam
• 93 Sunbird sedan : 2.0SOHC, Microsquirt, ported head, 10:1
• 88 Sunbird coupe : 2.0SOHC, turbo project car, giant tires