ok - i've read, and read, and read on the TCC issues. I've seen where people say, to determine what kind of issue you have, to unplug the electrical connector on the tranny. Here is the deal 87 IROC, rebuilt 700-R4. The shop SUPPOSEDLY put a non-locking converter in it. (don't ask) However, in 4th gear, at speeds over 45, the rpms jump around while coasting. Its as if the ECM is trying to lockup the converter and can't. To prove this, can i just unplug the connector on the tranny? Its NOT VSS, mechanical speedo. So will the only thing that unplugging that connector do, is stop the computer from trying to lockup the converter? I read that 86+ it won't overheat anything (esp if its true that its a non-locking converter) I just want to verify that its the ECM vs the TCC valve. WITHOUT hurting the car. Will unplugging that connector set an engine code? Kill the cruise? Or JUST stop the computer from trying to lockup the TC?

Thanks!

 

No issues with unplugging the connector on the trans. Won't set the SES or cause any problems. It will just prevent the TCC from locking via the ECM.

The RPMs jumping during coasting may be the DFCO. This is where the ECM cuts fuel to the engine to protect the cat-con and help with fuel mileage.

RBob.

 

DFCO??? What is that? Never heard of it? How do i test it/fix it?

 

Decel Fuel Cut Off, as posted it is a feature in the ECM that turns off the fuel injectors during coast-down. If the engine is modified the ECM may be going into and out of DFCO, as there are anti-stall tactics in the routine.

If the RPM drops too quickly or the LV8 goes up too quickly the ECM will exit DFCO as it thinks that the engine may be stalling. Then a few seconds later it can re-enter DFCO.

RBob.

 

You can be lazy and just put on the brakes a tad. you know where the brake lights come on.. that disengages the tcc also. So if its still jumping around then....?

 

actually, its fine if you slightly ride the brakes. Also fine until the car warms up some.

DFCO turns off the fuel injectors. Really? on an 87? I thought that was something only modern cars did......