TCC tweaking in $6E
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Joined: Jul 2001
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From: Western PA
Car: 1986 IROC-Z
TCC tweaking in $6E
I finally got around to installing a new cruise control brake switch, so I'm enjoying the wonders of a lockup torque converter once again. Trouble is, that switch had been broken for so long that I forgot just how touchy the TCC is on these cars with a factory tune. 
I'm running AUJM ($6E) code on an '86 IROC-Z with an L98 engine. I've done a lot of research on these forums regarding the TCC settings, but there are a few constants that I'm unsure of. I was hoping that someone might be able to fill me in on the details.
Looking at a $6E hack I have, the TCC section goes something like this:
Questions:
1. What routines use the values at $02A4 and $02A5? I thought that the TCC unlock vs. %TPS data was referenced from tables.
2. How does the value at $02A8 (32 mph) affect TCC unlock during coasting?
3. Where are the %TPS thresholds for TCC unlock during coasting? The other masks seem to have those constants. Are they hardcoded in $6E?
4. Related to the question above, is the value at $02A9 (8) the hysteresis value for those unseen %TPS thresholds?
I'd appreciate any help with these questions. It's been a while since I've tuned this car and I'm a bit rusty.
I'm running AUJM ($6E) code on an '86 IROC-Z with an L98 engine. I've done a lot of research on these forums regarding the TCC settings, but there are a few constants that I'm unsure of. I was hoping that someone might be able to fill me in on the details.
Looking at a $6E hack I have, the TCC section goes something like this:
Code:
L02A4 FCB 6 ; UNLOCK TCC IF DIFF %TPS G.T. 2.3% IN 12,5 Msec L02A5 FCB 9 ; UNLOCK TCC IF %TPS G.T 3.5% ; L02A6 FCB 29 ; DIFF TPS UNLOCK TIME (12 SEC'S) L02A7 FCB 120 ; LOWER TEMP LIMIT, (50 C) L02A8 FCB 32 ; COAST RELEASE, TPS SW POINT, (32 MPH) ; L02A9 FCB 8 ; TPS HYST FOR ; L02AA FCB 0 ; 0 SEC DELAY AFETER 4-3 DN SHIFT L02AB FCB 3 ; 300 msec DELAY BEFORE LOCK, LO GR AFTER COAST REL L02AC FCB 2 ; 200 msec DELAY BEFORE LOCK, HI GR AFTER COAST REL L02AD FCB 0 ; 0 MPH LOCK DELAY BYPASS MPH THRESH ; L02AE FCB 76 ; UNLOCK PREVENTION THRESH, (76 MPH) L02AF FCB 11 ; OFFSET TO Vss WHEN 3RD GR REQ, (0 MPH)
1. What routines use the values at $02A4 and $02A5? I thought that the TCC unlock vs. %TPS data was referenced from tables.
2. How does the value at $02A8 (32 mph) affect TCC unlock during coasting?
3. Where are the %TPS thresholds for TCC unlock during coasting? The other masks seem to have those constants. Are they hardcoded in $6E?
4. Related to the question above, is the value at $02A9 (8) the hysteresis value for those unseen %TPS thresholds?
I'd appreciate any help with these questions. It's been a while since I've tuned this car and I'm a bit rusty.
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From: Chasing Electrons
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Re: TCC tweaking in $6E
If you haven't already, head up to the Tuning Guide Book, chapter 5, '8063/'7747/'8746, TCC logic link. Explains a lot.
Here is better commenting of the $6E TCC parameters. The stuff in lower case is what I've updated over the years:
RBob.
Here is better commenting of the $6E TCC parameters. The stuff in lower case is what I've updated over the years:
Code:
LC2A4 FCB 6 ; UNLOCK TCC IF DIFF %TPS G.T. 2.3% IN 12,5 Msec LC2A5 FCB 9 ; UNLOCK TCC IF %TPS G.T 3.5% LC2A6 FCB 29 ; DIFF TPS UNLOCK TIME (12 SEC'S) LC2A7 FCB 120 ; LOWER TEMP LIMIT, (50 C) LC2A8 FCB 32 ; COAST RELEASE, TPS SW POINT, (32 MPH) LC2A9 FCB 8 ; TPS% for coast release, hi speed LC2AA FCB 0 ; TPS% for coast release, lo speed LC2AB FCB 3 ; TPS% HYST for Coast release LC2AC FCB 2 ; 200 msec DELAY BEFORE LOCK, HI GR AFTER COAST REL LC2AD FCB 0 ; 0 msec DELAY BEFORE LOCK, lo GR AFTER COAST REL LC2AE FCB 76 ; UNLOCK PREVENTION THRESH, (76 MPH) LC2AF FCB 11 ; OFFSET TO Vss WHEN 3RD GR REQ, (0 MPH)
Thread Starter
Joined: Jul 2001
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From: Western PA
Car: 1986 IROC-Z
Re: TCC tweaking in $6E
RBob, that's exactly what I was looking for. The TCC article you wrote is excellent. I'm glad you posted some better comments for the $6E parameters, too. After looking at disassemblies for the '730 ECM, I suspected that something must have been amiss. Thanks!
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Joined: Jul 2001
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From: Western PA
Car: 1986 IROC-Z
Re: TCC tweaking in $6E
I've been playing around with my TCC settings and I think I satisfied with the lockup speeds, but there's one glitch that I can't seem to solve. It pertains to the TCC lockup delay after shifting into 4th gear.
When the transmission shifts into 4th, it's followed almost immediately by a TCC lockup. It's quite annoying when accelerating at around 30% TPS. The transmission hits 3rd gear, the TCC locks up, then follows almost immediately with 4th gear and another lockup. The problem is that the engine RPM in 4th (no lockup) is higher than in in 3rd (lockup), so the engine revs up and down throughout this routine.
Short of setting the TCC speed limits to well above the 4th gear shift point, is there any way to remedy this situation? A lockup delay after shifting into 4th gear would be nice. I have a 2600 rpm torque converter. I don't think that a tighter converter would be reacting this way.
When the transmission shifts into 4th, it's followed almost immediately by a TCC lockup. It's quite annoying when accelerating at around 30% TPS. The transmission hits 3rd gear, the TCC locks up, then follows almost immediately with 4th gear and another lockup. The problem is that the engine RPM in 4th (no lockup) is higher than in in 3rd (lockup), so the engine revs up and down throughout this routine.
Short of setting the TCC speed limits to well above the 4th gear shift point, is there any way to remedy this situation? A lockup delay after shifting into 4th gear would be nice. I have a 2600 rpm torque converter. I don't think that a tighter converter would be reacting this way.
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From: Chasing Electrons
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Re: TCC tweaking in $6E
Additional corrections to the hac comments:
No guarantee that they are correct. I don't have a bench set up for the '7165 ECM.
But it looks like the culprit is at $2AC. There is a short unlock with a delay on the 3-4 upshift. Set it to zero and see if that does the trick.
If it doesn't work then check the ECM at pin C8. If there isn't a wire there then there isn't a 4th gear switch in the transmission. Which would then lead me to believe that there is a 'pulse' switch on the valve body causing the short unlock on the upshift. Which could easily be overridden.
RBob.
Code:
LC2AC FCB 2 ; 200 msec DELAY BEFORE LOCK, Lo->Hi gear upshift LC2AD FCB 0 ; 0 msec DELAY BEFORE LOCK, delay after any unlock
But it looks like the culprit is at $2AC. There is a short unlock with a delay on the 3-4 upshift. Set it to zero and see if that does the trick.
If it doesn't work then check the ECM at pin C8. If there isn't a wire there then there isn't a 4th gear switch in the transmission. Which would then lead me to believe that there is a 'pulse' switch on the valve body causing the short unlock on the upshift. Which could easily be overridden.
RBob.
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Joined: Jul 2001
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From: Western PA
Car: 1986 IROC-Z
Re: TCC tweaking in $6E
I appreciate the help, RBob. I'll have to do some testing and see how those memory locations work.
Thanks for the tip on the 4th gear switch, too. I think my ECM knows when the transmission is in high gear, but I'll check the wires to be sure.
Assuming that the ECM knows about 4th gear, is the unlock on the 3-4 upshift hardcoded into the calibration? Do you know if there would be any significant adverse affects to leaving the TCC locked up during the upshift?
Thanks for the tip on the 4th gear switch, too. I think my ECM knows when the transmission is in high gear, but I'll check the wires to be sure.
Assuming that the ECM knows about 4th gear, is the unlock on the 3-4 upshift hardcoded into the calibration? Do you know if there would be any significant adverse affects to leaving the TCC locked up during the upshift?
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Re: TCC tweaking in $6E
I appreciate the help, RBob. I'll have to do some testing and see how those memory locations work.
Thanks for the tip on the 4th gear switch, too. I think my ECM knows when the transmission is in high gear, but I'll check the wires to be sure.
Assuming that the ECM knows about 4th gear, is the unlock on the 3-4 upshift hardcoded into the calibration? Do you know if there would be any significant adverse affects to leaving the TCC locked up during the upshift?
Thanks for the tip on the 4th gear switch, too. I think my ECM knows when the transmission is in high gear, but I'll check the wires to be sure.
Assuming that the ECM knows about 4th gear, is the unlock on the 3-4 upshift hardcoded into the calibration? Do you know if there would be any significant adverse affects to leaving the TCC locked up during the upshift?
As long as the 3-4 up shift is under a light load, then the TCC will be OK. OTOH, GM does force the TCC to lock at 76-some MPH. Even at full throttle. So maybe the TCC is tougher then I give it credit for. OTOH (again), a modified engine is going to put a hurt on the TCC with full throttle lock ups.
The other way to go is to extend the re-lock delay on a 3-4 upshift. Make it 3 - 5 seconds. Much less irritating. Can also adjust the lo gear TCC lockup point (TPS% vs MPH) to not lock in 3rd under acceleration that would be used to get to 4th gear up shift.
That way it won't lock in 3rd (much of the time), then up shift to 4th where it will then lock up after a bit of delay. This isn't perfect as there will be times it still locks in 3rd (down hill slope). But does help the general driveability.
RBob.
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Thread Starter
Joined: Jul 2001
Posts: 1,000
Likes: 1
From: Western PA
Car: 1986 IROC-Z
Re: TCC tweaking in $6E
Thanks for clarifying how that all works, RBob. Your responses are always so insightful. Both of those techniques would probably work for my application. I'll have to take a few datalogs and see where the lockup and shift points intersect, and then begin tuning.
Both of those techniques would probably work for my application. I'll have to take a few datalogs and see where the lockup and shift points intersect, and then begin tuning. 
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