TCC won't unlock at the set low gears unlock speed

Hi! I want to get the TCC to stay unlocked up to 40 MPH and unlock at 38 MPH when slowing down. I already managed to get it to lock up at higher speed but it still let's me slow down to 25 MPH without unlocking. If I slow down below 40 MPH and briefly release throttle it won't lock again. Is some other parameter overriding the unlock speed? At the moment I have the lock up speed increased to 36 MPH and unlock speed to 34 MPH. I'll increase these as soon as I get an UV light to erase the EPROM.

The high gears load limit table seems also pretty weird. Is it trying to keep TCC locked at all speeds and loads? I'm pretty sure that everything TCC related is off due to changed diff ratio. The speedometer wasn't working when I bought the car so I guess the previous owners didn't even realize that the transmission has a lock-up converter.

Here's some info
1988 Chevrolet Caprice sedan with 4.3 liter V6
1228063 ECM with AKYD BCC. The ECM is remanufactured by GM at some point.
TH700-R4 with 2400 stall torque converter and 2.41 gears.

I'm a newbie with TBI tuning so any help is appreciated.

EDIT:
I measured the TPS. Idle 0,5 volts, WOT 4,3 volts and the voltage was linear in between.

I didn't want you to feel left out. I took a peek. What mask is this and is there an updated bin definition file? The one you left here sure is poor compared to the layout of some of the more popular definitions.

Thanks for your reply. I found the .xdf file here http://www.gearhead-efi.com/Fuel-Inj...hlight=1228063 It's the only file I could find for the 1228063 so I assumed it would be correct.

It may be correct, just its laid out very differently and the items do not have the extra explanation on what they do. I looked at the mod.bin and It does look like a $4d from the first line. What does the factory bin look like TCC wise, to compare? Not an expert, I just figured I would take a peek and bring the post up for others to look at.

Hi, Here is the original bin. Got my eprom eraser yesterday. :rockon: Now that I have all the tools I'm hoping to make some progress.

Post up a picture the same as above using the stock bin.

Any GM PCM I've dealt with uses %TPS for the table (so it goes 0-100) and then the points are mph. At a certain %TS if the vehicles gets above the lock MPH then the TCC locks. If the speed drops below the unlock MPH then the TCC unlocks. If the speed is between the ranges then the TCC stays how it was.

Your tables are just not making any sense to me. I can't figure out what would the 10-60 scale could possibly represent.

Quote:

---

Originally Posted by lionelhutz

Post up a picture the same as above using the stock bin.

Any GM PCM I've dealt with uses %TPS for the table (so it goes 0-100) and then the points are mph. At a certain %TS if the vehicles gets above the lock MPH then the TCC locks. If the speed drops below the unlock MPH then the TCC unlocks. If the speed is between the ranges then the TCC stays how it was.

Your tables are just not making any sense to me. I can't figure out what would the 10-60 scale could possibly represent.

---

I know this is an older post, but the older TBI TCC stuff is just plain backwards to the newer stuff. The 10-60 scale is MPH. The value in the table is TPS. Still works basically the same way.

Any update to this problem?

Attachment 14169
Here is the original bin opened with $4D. Now there seems to be another unlock speed parameter that wasn't visible before. I hope this parameter is responsible for the problems. TCC load limits also look more sensible now.

700r4 original? does it have the correct internal lock up harness? does your speedometer bounce around alot especially at low speed? i know my 88 caprice does. VSS signal comes from an optic sensor on the back of the speedo head. maybe it is worn and causes an erratic signal which is maybe why it locks up at different mph?

Quote:

---

Originally Posted by tayto

700r4 original? does it have the correct internal lock up harness? does your speedometer bounce around alot especially at low speed?

---

I think it's 700R4 original. Not sure about the harness. It has a B&M rebuilt transmission with 2400RPM torq converter. Speedometer needle doesn't bounce but it doesn't show actual speed. When I'm doing 100 kmph it shows only ~85 kmph. It's an export model with metric instrument panel.

TCC is working now. TCC [High Gears] unlock was keeping it locked. When I used correct .xdf ($4D) to open the .bin I was able to adjust the unlocking speed.

What is the deal with "high gears" and "low gears" settings? It's pretty weird that "high gears" setting is keeping TCC locked when the transmission is in third gear.

I also had to manually change mask byte from 4D to AA to make ECM to skip checksum test to make it work.