Re: TC lockup problems

[Roger Heflin <rah@horizon.hit.net>]

On Wed, 28 Jun 2000, Bruce Plecan wrote:

> > Under WOT we are seeing consistent knock retard of 1-2 degrees at 82mph.
> > Furthermore, the Engine RPM DECREASES approximately 150rpms even though
> you
> > have the throttle nailed.  Under further inspection we determined that the
> > TC was locking up at exactly that same mph.  This explains the RPM drop
> and
> > the slight knock.
> > What could be causing the TC to lockup??
> 
> It's in the program to do that, least as I recall.
> No TCC lock up = no tranny cooler.
> 
> > Could the use of the 305 tables cause this??
> 
> Might have different speed setting.
> 
> > Is the PROM the only control for TC lockup?
> 
> No, there is a brake pedal switch, and pressure sensor in tranny.
> Grumpy

After seeing bruces post, there are external ways to unlock it, there
are no "as designed" ways to lock it outside of the PCM.  

THe PCM is locking it, and at least on mine, GM designed it to lock at
a certain rpm no matter what the throttle position.  I do know that
they have changed the speed that this happens at quite a bit, as there
appear to be several different lockup points for different 93 Z28 just
depending on the prom rev.

If you have a bigger cam, you will want to adjust this up.

And on my web site http://www.hit.net/~rah under prom work there are
some flowcharts that show the TCC/tranny control flowchart for my car
(my guess is that yours is very similar, but probably different in
some minir ways).

The flowchart is actaully at http://horizon.hit.net/~rah/EDD3_EF37.gif
and is pretty big, and is pretty hard to read, but around a label of
EF1A there is the code that compares speed, and locks no matter what.

All of the 93+ LT1 cars seem to do this, I had not heard of GM using
it on older cars (because no one had mentioned it or noticed it).  The
speed does vary on the 93+ cars, but it is always there.

				Roger

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo@lists.diy-efi.org