TH400, 7747, and/or 8746
07-03-2007, 12:57 PM
#1
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Car: 87 Suburban 2500
Engine: 455 Wildcat ( somewhat modified ))
Transmission: TH400 ( for now )
Axle/Gears: 4.10 ( for now )
TH400, 7747, and/or 8746
Got the 7747 which came stock in the truck, tweeked and working OK.
Looked at the 8746, decided I liked some of that code, and swapped in the 8746.
Mostly, works just fine, except the TH400 electric kickdown.
The "stock" 8746 code mostly holds the trans IN kickdown, and hanging low gear with a 4.10 axle is noisy, and not too good on gas, so disabeling most all of the TCC options lets it up-shift.
Punching it hard also let it upshift. I suspect that the 8746 thinks it's controlling a TCC, as it certainly behaves that way, kicking down when a TCC should lock, and vice versa. Duplicating the TCC settings from the 7747 into the 8746 as much as possible doesn't work. My suspicion is the settings and load arrays in the 8746 that don't exist in the 7747, combined with my ignorance. Since the 7747 controlled kickdown fine, the 8746 should ?? Presently, I've disabled the TCC settings completely, so there's no kickdown at all, which is driveable, but hardly desireable.
If this belongs in another forum, feel free to let me know, nicely or not.
THANKS in advance for any help whatever.
Looked at the 8746, decided I liked some of that code, and swapped in the 8746.
Mostly, works just fine, except the TH400 electric kickdown.
The "stock" 8746 code mostly holds the trans IN kickdown, and hanging low gear with a 4.10 axle is noisy, and not too good on gas, so disabeling most all of the TCC options lets it up-shift.
Punching it hard also let it upshift. I suspect that the 8746 thinks it's controlling a TCC, as it certainly behaves that way, kicking down when a TCC should lock, and vice versa. Duplicating the TCC settings from the 7747 into the 8746 as much as possible doesn't work. My suspicion is the settings and load arrays in the 8746 that don't exist in the 7747, combined with my ignorance. Since the 7747 controlled kickdown fine, the 8746 should ?? Presently, I've disabled the TCC settings completely, so there's no kickdown at all, which is driveable, but hardly desireable.
If this belongs in another forum, feel free to let me know, nicely or not.
THANKS in advance for any help whatever.
07-03-2007, 07:28 PM
#2
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Re: TH400, 7747, and/or 8746
The '8746 should work for a TH400 kickdown. Basically, the coast unlock terms are used. Everything else is max'd or min'd. This is modified from another post I made on a different code base. It gives the basic settings:
Set Lock enable CTS to -40C
Set Relock delays to 0 (both)
Set Forced Lock to 255 MPH
Set the 4 TCC TPS% unlock/lock tables to 100%:
TPS% required to unlock vs. mph
Set the 4 MPH thresholds to 0:
force unlock < mph thres
Set the 4 MPH thresholds to 255 (may already be):
force unlock > mph thres
Set the TPS% Decel unlock values to 85%:
For hyteresis set this one at a low value (GM sometimes used 10%)
tps decel unlock hyst
With these settings the TCC ECM output will go low when the TPS% is greater then 85%. The Relay is set up to provide +12 volts to the downshift solenoid whenever the TCC ECM output goes low (grounded).
And the tables that go with it (these are '8746):
We'll shufflle the thread over to diy_prom. . .
RBob.
Set Lock enable CTS to -40C
Set Relock delays to 0 (both)
Set Forced Lock to 255 MPH
Set the 4 TCC TPS% unlock/lock tables to 100%:
TPS% required to unlock vs. mph
Set the 4 MPH thresholds to 0:
force unlock < mph thres
Set the 4 MPH thresholds to 255 (may already be):
force unlock > mph thres
Set the TPS% Decel unlock values to 85%:
For hyteresis set this one at a low value (GM sometimes used 10%)
tps decel unlock hyst
With these settings the TCC ECM output will go low when the TPS% is greater then 85%. The Relay is set up to provide +12 volts to the downshift solenoid whenever the TCC ECM output goes low (grounded).
And the tables that go with it (these are '8746):
Code:
;-----------------------------------------------
;
; TCC parameters
;
;-----------------------------------------------
LD4B6: FCB 102 ; 60c, min coolant for tcc lockup
; indexed table entries
LD4B7: FCB 3 ; flag to use tps% for decel TCC unlock
LD4B8: FCB 40 ; mph thres for tps% decel unlock limit, w/5 mph hyst
LD4B9: FCB 10 ; 3.9%, tps decel unlock limit when < 40 mph (LD4B8)
LD4BA: FCB 21 ; 8.2%, tps decel unlock limit when > 40 mph (LD4B8)
LD4BB: FCB 4 ; 1.6%, tps decel unlock hyst
;-----------------------
LD4BC: FCB 0 ; N/U
LD4BD: FCB 128 ; filter coef for MPH / 1, L0030
LD4BE: FCB 1 ; 0.1 sec, upshift unlock to relock delay
LD4BF: FCB 6 ; 0.6 sec, re-lock delay
LD4C0: FCB 80 ; mph thres for mandatory lockup of tcc
;-----------------------------------------------
; TCC, Low Gear tables
;-----------------------------------------------
LD4C1: FCB 38 ; force unlock < mph thres (use if unlocked)
LD4C2: FCB 255 ; force unlock > mph thres (use if unlocked)
LD4C3: FCB 36 ; force unlock < mph thres (use if locked)
LD4C4: FCB 255 ; force unlock > mph thres (use if locked)
;-----------------------------------------------
; 2d lkup's w/SBA
;
; TPS% required to unlock vs. mph
;
; tps% = val * .39
;-----------------------------------------------
; mph: 20 24 28 32 36 40 44 48 52 56 60
; min tps% to unlock (currently locked):
LD4C5: FCB 2 2 19 58 68 72 78 82 104 120 120
; min tps% to stay unlocked (currently unlocked):
LD4D0: FCB 1 1 8 10 27 37 45 52 64 90 96
;-----------------------------------------------
; TCC, High Gear tables
;-----------------------------------------------
LD4DB: FCB 32 ; force unlock < mph thres (use if unlocked)
LD4DC: FCB 255 ; force unlock > mph thres (use if unlocked)
LD4DD: FCB 30 ; force unlock < mph thres (use if locked)
LD4DE: FCB 255 ; force unlock > mph thres (use if locked)
;-----------------------------------------------
; 2d lkup's w/SBA
;
; TPS% required to unlock vs. mph
;
; tps% = val * .39
;-----------------------------------------------
; mph: 20 24 28 32 36 40 44 48 52 56 60
; min tps% to unlock (currently locked):
LD4DF: FCB 2 2 10 56 74 88 97 112 120 120 120
; min tps% to stay unlocked (currently unlocked):
LD4EA: FCB 1 1 8 22 41 51 69 84 90 90 96 RBob.
07-03-2007, 08:03 PM
#3
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Car: 87 Suburban 2500
Engine: 455 Wildcat ( somewhat modified ))
Transmission: TH400 ( for now )
Axle/Gears: 4.10 ( for now )
Re: TH400, 7747, and/or 8746
Thanks,
In all my googling, I had found that post about the EBL and kick-down, and tried as closely as I could, those settings. What it gave me, was NO kickdown. ( which was much better than always kicked-down ) I suspect it's the tables at LD4C5 and at LD4DF, but am not sure.
Then, I looked back into the 7747, which does kickdown, and tried to adapt those settings, again finding code differences my feeble single functioning brain cell doesn't quite get.
( I'm actually OK with !logic sometimes, but... )
So, I plugged the 7747 back in, and it still works fine. Gotta be me.
I'd tried something similar to what you posted, then went more extreme. Min temp to 10c, coast values to 50%, stuff like that. No joy. ( this motor has enough torque that if I'm above 50% TPS something is very wrong, or I've got 10K pounds on the hitch )
Three or four more burns, and finally decided I'd ask.
Since you were kind enough to post the whole relevant sections, I'll try those numbers exactly, tomorrow, and have the result by noon or so.
I understand that it was bench tested, and should work, but real world and differing ECM code being what it is........
When it does work, I'll post the results, and the exact settings that do work.
Then, we'll blow somethign else up ! ;-)
In all my googling, I had found that post about the EBL and kick-down, and tried as closely as I could, those settings. What it gave me, was NO kickdown. ( which was much better than always kicked-down ) I suspect it's the tables at LD4C5 and at LD4DF, but am not sure.
Then, I looked back into the 7747, which does kickdown, and tried to adapt those settings, again finding code differences my feeble single functioning brain cell doesn't quite get.
( I'm actually OK with !logic sometimes, but... )
So, I plugged the 7747 back in, and it still works fine. Gotta be me.
I'd tried something similar to what you posted, then went more extreme. Min temp to 10c, coast values to 50%, stuff like that. No joy. ( this motor has enough torque that if I'm above 50% TPS something is very wrong, or I've got 10K pounds on the hitch )
Three or four more burns, and finally decided I'd ask.
Since you were kind enough to post the whole relevant sections, I'll try those numbers exactly, tomorrow, and have the result by noon or so.
I understand that it was bench tested, and should work, but real world and differing ECM code being what it is........
When it does work, I'll post the results, and the exact settings that do work.
Then, we'll blow somethign else up ! ;-)
07-04-2007, 10:15 AM
#4
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Car: 87 Suburban 2500
Engine: 455 Wildcat ( somewhat modified ))
Transmission: TH400 ( for now )
Axle/Gears: 4.10 ( for now )
Re: TH400, 7747, and/or 8746
Thanks, yet again.
Success !! Using your suggestions exactly, it works.
By tweeking the TPS% Decel unlock values it kicks anywhere I choose.
Much better than a loud pedal switch, or throttle linkage arrangement.
Couple items not in Jon's original XDF file, so now I suspect that was the reason
I couldn't get it before.
For those who don't have either the TH400 electric kickdown, or a TCC, I can see
where this can be easily used for other things, like kicking out AC on acceleration,
lighting a warning lamp at TPS% PE engagement, stuff like that.
Wonder why it hadn't come up before ?
Success !! Using your suggestions exactly, it works.
By tweeking the TPS% Decel unlock values it kicks anywhere I choose.
Much better than a loud pedal switch, or throttle linkage arrangement.
Couple items not in Jon's original XDF file, so now I suspect that was the reason
I couldn't get it before.
For those who don't have either the TH400 electric kickdown, or a TCC, I can see
where this can be easily used for other things, like kicking out AC on acceleration,
lighting a warning lamp at TPS% PE engagement, stuff like that.
Wonder why it hadn't come up before ?
Last edited by Cflick; 07-04-2007 at 10:18 AM. Reason: Additional comment
07-04-2007, 11:21 AM
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Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Re: TH400, 7747, and/or 8746
Thanks, yet again.
Success !! Using your suggestions exactly, it works.
By tweeking the TPS% Decel unlock values it kicks anywhere I choose.
Much better than a loud pedal switch, or throttle linkage arrangement.
Couple items not in Jon's original XDF file, so now I suspect that was the reason
I couldn't get it before.
For those who don't have either the TH400 electric kickdown, or a TCC, I can see
where this can be easily used for other things, like kicking out AC on acceleration,
lighting a warning lamp at TPS% PE engagement, stuff like that.
Wonder why it hadn't come up before ?
Success !! Using your suggestions exactly, it works.
By tweeking the TPS% Decel unlock values it kicks anywhere I choose.
Much better than a loud pedal switch, or throttle linkage arrangement.
Couple items not in Jon's original XDF file, so now I suspect that was the reason
I couldn't get it before.
For those who don't have either the TH400 electric kickdown, or a TCC, I can see
where this can be easily used for other things, like kicking out AC on acceleration,
lighting a warning lamp at TPS% PE engagement, stuff like that.
Wonder why it hadn't come up before ?
It is easy enough to re-assign some of those things. I re-assigned the AIR Divert output to control my A/C compressor clutch when I was still running the 7747.
The later model TBI PCMs have about 7 extra outputs that can be re-assigned if not using an electronic transmission
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