Okay, I have been tracking down a problematic TCC lately. So far, I have hooked up a test light between ALDL terminal F and 12 positive. I have also hooked up a switch between ALDL terminals A and F. I can go down the road and watch when the ECM is telling the converter to engage. I can also hit the switch and manually lock the converter.

Upon driving down the road, I noticed the ECM would disengage the converter whenever I slightly let off the throttle, I mean SLIGHTLY! Basically the ECM is locking/unlocking the converter at will. However, when I hit the switch, the converter locks and stays locked. Therefore, I don't think the problem is in the TCC solenoid or wiring.

Lastly, I did notice that when slowing down from speed with the brakes on, the converter would sometimes lock. This seems very confusing because isn't the ECM suppose to unlock the converter whenever the brakes are pressed? Is the ECM fried?


Any and all help is appreciated,
Bill

 

By the way, I have recently replaced and checked my TPS and that seems fine.

The problems described above are on a 87 Camaro that was a lg4 and is now a 383. Still has stock computer and quadrajet.

Thanks,
Bill

 

Another update, I just went for a cruise and got the dreaded service engine light for about 10 seconds while stopped at a stoplight. When I got home and read the trouble codes, I got codes 21 and 34. Code 21 is for the TPS, while code 34 is for the vacuum sensor.

I have checked the TPS sensor at the plug using a voltmeter. It seems to be fine and have a smooth linear voltage progression. However, when adjusted to .5 -.6 volts at idle, I only get about 4 volts at WOT. This is not a major concern because I can compensate for WOT with secondary metering rods.

I do not know how to check the vacuum sensor so I am not sure its status.

However, since the TPS seems to be correct, this leads me to believe something is not right with the ECM. So is this an ECM issue? Also, what is more likely to be the problem, the ECM or PROM?

Thanks

 

3...2...1...BUMP

 

I know the answer to this one: The TCC lock-up solenoid power goes through the brake switch, so hitting the brakes takes the power away from the solenoid. The ECM doesn't unlock because the brakes are on (there isn't any brake input to the ECM).

Otherwise, I'm not sure. I thought the ECM used manifold vacuum as an input for the TCC lock-up as well as TPS, but I certainly don't know any details.

 

I see, so when I hit the brakes and still see the test light on, that is really a false positive. The converter is unlocked, but the ECM doesn't know that I am using the brakes thus still sending the signal and lighting the test light. Got It!

As for the manifold vacuum sensor, I tested it similar to the TPS checking the B wire. However, I don't know what the output should be from the sensor? I have seen in searching how the MAP output looks, but this being a vacuum sensor I imagine has a different output.

Thanks five7kid, I has noticed in searching that you have covered this topic alot.

 

By the way, when I cruise down the road and let-off the throttle, should the TCC unlock? It unlocks for about 2 seconds then locks while the car is deccelerating.

 

That's normal. Keeps it from jerking (same reason for the 4-3 switch).

When I use the cruise accelerate function on the flat, say from 65 to 70, it will go up to the new speed with the TCC locked. As soon as I let go of the button at the new speed, it will unlock for a couple of seconds, then relock. Strange, but true.

That's because I hassled with it for a couple of years before getting it to work. A lot of research and ?'s in the process.