TC lockup problems

[Roger Heflin]

On Wed, 28 Jun 2000, TRAX wrote:

> I'm running into an oddity with a friend's car that is becoming increasingly
> difficult to troubleshoot.  The car is a 1991 Z-28 305TPI automatic.  This
> car has a transplanted 350 (w/ 350 knock sensor), 2400 stall converter, and
> 3.42 gears.  He is running a custom PROM in the 730 ECM.  The ScanMaster
> scan tool that we are using shows that his TC is locking up under WOT at
> approximately 82mph.  All TC lock and unlock values in the tables are the
> same as the stock 305 tables.  The Lock and Unlock mph contants have been
> upped 19mph.
> 
> 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??
> Could the use of the 305 tables cause this??
> Is the PROM the only control for TC lockup?
> 
> Tim

Beyond the "table" that is listed, there is a hard lockup in my
computer (93 LT1 Z28),  of 95 mph, and it will lockup at that no
matter what the TPS is.   I would expect that yours also has it, the
value is not in a table, it is all by itself and outside the table.

On mine I never obviously noticed the lockup before getting a high
stall convertor (the rpm drop was not enough to notice), after the
high stall convertor it was noticable, and it was even more noticable
after getting a larger cam since the engine now bogged.

The computer does not get status back from the TC, it tells the TC to
lockup, and it is only a one way communication, so the computer is
telling it to lockup (well unless you ground the correct ALDL pin),
and in that case I don't know that the comuter will even realize that
the TC is locked, unless it does I some feedback which would suprise
me.

			Roger

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