WOT Downshift Shift Speeds

[DrkPhx]

Hi,
This is just for reference, but I thought I would post it in case someone stumbles across the same issue. Other's may already know this, but anyway here it is.

I've been tuning a friend's 00 4WD Silverado in which he installed a 6.0L with LS3 heads, L99 intake and a LS6 cam. All went well except for a nagging problem where the truck wouldn't WOT downshift at certain speeds. After multiple attempts tweaking the various trans tables (and a lot of time searching various boards and threads) I couldn't nail it. I've tuned muitiple A4 cars (and my TB SS) without this problem, so I was baffled. Well I finally figured it out.

The mph values in the WOT Downshift Shift Speed tables in this particular PCM are a ceiling and not a floor value. Example: WOT 2>1 table is set at 30 mph. The PCM will allow a 2>1 downshift at any speed under 30 mph but will not WOT downshift above that value. So this is the maximum speed the PCM will allow a 2>1 downshift; nothing more. Same applies to all of the WOT Downshift Shift Speed tables.

While this is hardly ground breaking, consider the same table in my 98 TA is a floor value; meaning you set the value purposely low (if desired) so the PCM will WOT downshift at anything above the mph value.

I didn't realize the same trans tables in different PCM's have different qualifers. That's what was driving me nuts. Once again, hardly earth shattering and may be well known to others, but it was something that just hit me so I thought I would pass it along.

[joecar]

Yes you are correct, tables D0906-8, D0925-37, D0966-7 are ceilings/maximums (downshift is triggered/allowed when operating point passes to underside of curve).

The table descriptions are very brief ("Controls the xxxx Mode x->y downshift") and lack any detail/explanation, you and I had to find out for ourselves.

Hmmm, that's very strange on the 1998, are you sure, it makes the WOT downshift parameters totally useless (allows a downshift from above 30 mph even if this will send the rpm into valve-float-bent-pushrod region)... ...but, then again the 1998's are strange anyway

Also, need to watchout for the throttle kickdown tables, if they are not at all 100% they can override/interfere with the WOT/PT downshift tables (on trucks they are typically not at 100%).

[DrkPhx]

Hmmm, that's very strange on the 1998, are you sure, it makes the WOT downshift parameters totally useless (allows a downshift from above 30 mph even if this will send the rpm into valve-float-bent-pushrod region

You're probably right. A long time ago, I set the values in the WOT Downshift tables real low and they work fine. Maybe the low value disabled the tables. It's never over revved on a downshift. I may look into it when the weather is nice enough to take the car out.