Tuning question for 730 ECM

[Shannen Durphey]

I believe it's TCC.  But if you've changed the mph value in the prom
and the tcc still applies, there must be something else controlling
it.  Looking at mph on the scan tool is no guarantee that you're
seeing what's actually happening, only the symptoms.  A quick glance
through the ANHT hac tells me RPM can also be a factor in tcc apply. 
What's your load value when TCC applies?  What's the RPM?  Is the TCC
RPM vs MPH bit set for MPH?  Have you tried modifying anything in the
TCC tables besides the TCC unlock prevention threshold?

The question about disconnecting VSS was to help determine whether or
not the ecm is using mph or some other factors to lock tcc.

Don't trust scan tools when it comes to tcc diagnosis.  

Guys in GM dealerships were making those "magic harnesses" back in the
early 80's, when GM thought it was wise to lock TCC around 27mph. 
Sometimes TCC locked before the car got out of the driveway.  Talk
about dogs... : )
HTH
Shannen

timsiford at hushmail.com wrote:
> 
> >Are you sure it's only a speed related TCC apply?   What happens if
> >you disconnect the VSS?
> 
> I'm pretty darn sure.  However, let me give credit where credit is due.
>  Greg Westphal and Jeff Fox discovered this.  I confirmed it.  Using a scan
> tool the TCC apply happens at a particular mph.  This is a mandatory lockup
> and the anht_hac.pdf confirms the mph.  TCC applies, RPMs drop, and MPH
> keeps increasing.  Funny thing is ... Diacom doesn't report the TCC apply.
>  Greg and Jeff found it using an OTC scanner (I think).  Furthermore, Greg
> installed a TCC lock harness ...
> 
> "I installed a TCC lock-up harness that keeps the TCC from locking up in
> any gear but 4th. Poof! Problem gone!  The harness installs between the
> 4-pin harness going to the tranny and the corresponding connector on the
> left side of the tranny. You can find one for about $35-40 at Summit or
> Jegs..."
> 
> Tim
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