Hello all I am new here and I have a transmission issue.

I have a 1994 Bonn. in which I have transplanted the drive train of 1994 Buick Lasaber.
The new drive train has 47000 miles on it. The engine runs fine but the transmission has to be cold to shift into overdrive after 7-10 miles it will no longer shift into overdrive or lock up the torque converter. At 60 mph the rpm’* when in OD and TC locked are about 1500-1600. When not in OD it is 2500-2600. I have replaced the vacuum modulator and changed the tranny fluid. I don’t know of any differences between the Buick and the Pontiac to cause this. I have read on this web sight about wiring troubles and shift solenoids. How do you test for a wiring problem or a solenoid problem? I really need to fix this soon so any help is greatly appreciated.

I think the first thing you need to do is hook up a scantool, and go for a drive. You need to see if the PCM is even commanding TC lockup, and if it is, to see the slip RPM'*.

Thanks for the reply willwren.
I will get it on a scan tool as soon as I can.
When it shifts it shifts fine then it just stops. I don’t understand why it only works when cold. Why would that make a difference?

It sounds as if reverse logic is being applied here. The PCM normally won't allow TCC engagement until it receives input from the ECT sensor that the engine is warmed to a specific temperature.

Thanks markwb
Not sure, what an ECT is or were it is located.
Is it possible I wired it up backwards?
I had to swap the engine wiring harnesses and a couple of sensors because the Buick was all idiot lights and of course, the Bonn, is all gauges. I’m not an idiot I just don’t have all the lingo down yet

Thanks again for the help.

I'll be home in a couple hours. I'll dig in the factory service manuals and see what I can figure out.

I really appreciate that willwren
It’* nice to finally find a site with this kind of expertise

I'm still researching, but you should start by looking at the schematics on my website here:

http://www.williamwren.com/Bonnevill...umba/page1.htm

Note some minor differences. You should be able to find which wires/pins the thermistor is located on. I'm betting something was slightly different in wiring between the transaxles of the two cars. It should be simple, and maybe as simple as simply reversing two wires. Keep this thread going to keep us updated.

Engine Coolant Temperature. Should be located in close proximity to thermostat. housing. But I'm not necessarily saying there is a fault with the ECT, only the way in which the PCM interprets the signal for purposes of TCC engagement. Like Bill said, it could be as simple as two leads reversed there.

Memory coming back to me here.....we had a new member in the last 3 or 4 months that did a swap, and found a wiring difference. Anyone remember where that thread is?