MikeT 88IROC350

I got the idea from these boards to wire up the "upshift" idiot light to the TCC lockup. Works great, but now I see the light flipping on and off when I am near the lock/unlock constants that I have set. Is this normal? I am locking at 40 unlock at 37 in 4th. But I also noticed it flipping right around 40-45 mph. Kind of depends on the road conditions, as in a slight hill on a back road, with light throttle applied.

I have messed with the lock/unlock tables a little bit, but not much different than stock. I don't think I am near the %tps and speed to cause the TCC to flip on and off.

I was just wondering if other folks have seen this happen, or maybe it is normal.

funstick

there a good write up over the the GMECM site on GM TCC strategy. basically GM thinking is to leave it on unless the is a reason for it to be off.

John Millican

iTrader: (1)

If you let up on the gas, even slightly it will unlock. Same thing for the brakes, the moment you tap the brakes it will unlock.


Also locking at 40 mph is too low. With my car I set the lock at 50 mph. Drives much better. I still had the un-lock problem when I let up on the gas or was coasting. That's a GM design. There is a way to fix it in the prom though.

funstick

yeah change the tps unlock % to 0. but you really dont want thh TCC to stay locked in a decel mode. it will lead to stalling not to mention the shock loads the clutch will see.

MikeT 88IROC350

Thanks for the tips fellas. I will check out that reading material on the GM site. I had my TCC locking higher, closer to 50, but that was with my stock 2.77 gears. Worked good, let the engine wind out a little more before kicking down.

But when I put the 3.73s in, I had this idea that I should be locking the TCC sooner, to help with gas milage and whatnot. The gear change was a big step, so the motor revs out much more.

I just have this back road that I drive to get to my house, so I don't get up to full cruising speed. I usually run it around 45. Sure I could go faster, but I am in no hurry like many people in this world. I use a light throttle, on and off for the hills, but don't usually touch the brake.

Good ideas, keep'em coming.

Ed Maher

Hey John, i actually tried that code change you talked about in your earlier post on this and i found that the TCC would still unlock during what i am guessing was DFCO (didn't have access to a scan tool while i was running that bin) The TCC would then relock when it left DFCO. So basically lifting off the throttle on a downhill at highway speed was pure hell on the TCC since it would hit DFCO, the RPMs would drop to near idle (i also have a 3k stall vigilante so i get little engine braking through the converter) and the DFCO would kick off and the TCC would lock back up and the engine would jump back up to the 2k or whatever RPMs corresponded to my road speed.
I haven't had the time to verify it was DFCO, nor go through the code myself, just wondering if you saw anything similar, or maybe had DFCO disabled or something. It could also be that i was working with a 305 bin which might have a different strategy.

John Millican

iTrader: (1)

Not sure Ed. I tried the DFCO switch both ways in the "ECM Switch Tables". It didn't keep the TCC from un-locking at all. The only thing that did help was the hac I got from the older post a month or more ago. That did the trick.
I don't have hills around where I am so I can't duplicate your problem.

MikeT 88IROC350

I read that article over on the GM site. Good info, have to print that out and memorize it. Today's drive into work and later back home gave me some info. My TCC does not unlock when the brake is applied. I guess some cars will do that. But it does seem to follow my unlock and lock constants which I have set into the PROM.

When I got on the gas a little bit today from a redlite, the engine wound out a little in 3rd, then went to 4th, and the TCC lock maybe toggled 3-5 times before locking. I was well above my lock speed at that time, and most likely backing off on the TPS. I didn't use my scan tool, just watching the upshift light.

I can also accept that DFCO mode affecting the TCC lockup. Don't really want to go there at this point!

funstick

i would be inclined to agree with the statement that the TCC will unlock in DFCO the shock to the converter clutch would be hell on it. a stock converter will likely fail if running in this mode for an extedned period of time. the aftermarket converters however have stonger better clutchs and will most likely stand up to the abuse a high compresion engine can toss out.