7747-7427 Swap

[Scooterwrench]

Hey Folks.
Anybody out there done a 7747-7427 ECM upgrade?
I've got a 7427 coming to upgrade the ECM in ol Smoky and read the swap thread on the gearheadefi site. Everything looks pretty straight forward with he exception of the TCC pin. They're saying to use E11 to drive the TCC which is the PWM TCC solenoid output. Pin E10 is the direct TCC output. Could using pin E11 cause the TCC to slip because it's not getting a direct ground?

 

[L31MaxExpress]

Hey Folks.
Anybody out there done a 7747-7427 ECM upgrade?
I've got a 7427 coming to upgrade the ECM in ol Smoky and read the swap thread on the gearheadefi site. Everything looks pretty straight forward with he exception of the TCC pin. They're saying to use E11 to drive the TCC which is the PWM TCC solenoid output Pin E10 is the direct TCC output. Could using pin E11 cause the TCC to slip because it's not getting a direct ground?

Not if you use the correct transmission setting. Have to select the option for Non-Computer Transmission in the programming. Most of the writeups on the subject where robbed from my old TGO post.

 

[Scooterwrench]

OK, I'll study the $0D XDF.
Guess I should have mentioned that my truck has a 700R4.

 

[L31MaxExpress]

OK, I'll study the $0D XDF.
Guess I should have mentioned that my truck has a 700R4.

My 83 G20 that I swapped from a 299 to a 7427 did as well. The TCC output is on E11 and it requires 12V on the brake light switch input wire for the PCM to lock the converter. I used a leftover 12V wire in the ECM harness as my TCC was wired to where the brake switch released it without having the 12V signal cut from the PCM anyway.

 

[Scooterwrench]

I was just looking at the 91 driveability manual. It shows 12V supplied to the the TCC sol. through the brake pedal switch. You lost me on the with your leftover wire explanation. Are you talking about pin E13?

 

[L31MaxExpress]

I was just looking at the 91 driveability manual. It shows 12V supplied to the the TCC sol. through the brake pedal switch. You lost me on the with your leftover wire explanation. Are you talking about pin E13?

Sorry, pin E13 needs 12V power for the PCM to ground pin E11. The un-used wire I mentioned was a 12V source wire to the old 7747/299 not used with the 7427 swap.

 

[Scooterwrench]

Gotcha! 12V constant or switched?
Any idea why pin E10 is not used? That is supposed to be the TCC sol. wire. Just curious!!!

 

[L31MaxExpress]

Gotcha! 12V constant or switched?
Any idea why pin E10 is not used? That is supposed to be the TCC sol. wire. Just curious!!!

I put constant to it, because that is what I had easily available without splicing. Never cause a parasitic draw.

No idea why GM choose E11 rather than E10 other than perhaps the fact that E11s output is interrupted by the loss of voltage at E13 at the circuit level. Reversing the code, the non ecm controlled automatic TCC output is on E11. No output from E10. E2 is the shift light output for a manual transmission.

 

[Scooterwrench]

Cool! Thank you!!!
So the TCC sol. is switched off on both sides. Ground breaks in the PCM and hot breaks by the brake pedal switch. Or does having the constant 12V on E13 keep E11 grounded?
What about the high gear switch(7747 pin C7)? I know there is no input on the 7427 for it. Is the TCC lockup being applied by VSS vs MAP vs TPS?

 

[L31MaxExpress]

Cool! Thank you!!!
So the TCC sol. is switched off on both sides. Ground breaks in the PCM and hot breaks by the brake pedal switch. Or does having the constant 12V on E13 keep E11 grounded?
What about the high gear switch(7747 pin C7)? I know there is no input on the 7427 for it. Is the TCC lockup being applied by VSS vs MAP vs TPS?

It is applied by TPS vs VSS with a minimum MPH threshold to unlock and lock. The 4L60E trucks cut the power to E13 thus disabling the ground to E11. If you felt inclined you could pull a wire from the brake switch to E13. The 700r4 wiring already cuts the power feed. Its only needed for abrupt hard braking, where the rear wheels might lockup suddenly, stalling the engine. In normal driving the TCC will unlock when you drop below the minimum speed. Never really seen any of the 700r4 TBI trucks use different tables for 2nd/3rd gear vs 4th gear. Hence I am not even sure why the high gear pressure switch exists.