$E6/$0D '8625/'7427 AC clutch control

[ben73]

Hi Guys,

Is anyone else still playing with the '93-95 TBI PCMs?
I've had one in my 383 '84 Corvette for over 18 years. It now got a WBo2 input, fan control, 4L60e etc etc.

I see that the code allows for A/C clutch control.
It looks like it's made active by selecting x400F bit 2.
I'd like to use it to enable the A/C to be turned off at high TPS% and RPM. It also allows for an A/C clutch engagement delay of a few seconds when starting the engine which would be nice.

It looks like the code was there but possible never used?
Does anyone know which of the unused pins on the ECM it is coded to control?
I've tried to figure it out by reading the code but my assembly knowledge is not great and I don't know how the pin addressing works in the code either....

I'm going to test a few of the spare pins to see if I can find it. I will start with E3 as I believe it's the (also unused) 'CPI tuning valve' and I *think* when x400F is not selected, it means you with to activate this option instead of the clutch control(?)

Does anyone know?

[tayto]

Looks like AC signal is on E12. Have not seen AC relay control like the older C3 ECMs have.

[ben73]

Yes that's correct. I have it running that way currently.
The PCM knows when the clutch is energised, turns on the 'AC Requested' flag on the ALDL and adjusts the idle speed etc as per the AC relevant tables.

But the PCM has no control of the AC clutch.

I have now confirmed that pin E3 plays a part, but I haven't yet figured out it's operation.
If x400F bit 2 is selected (AC Control Mode), a test lamp connected to E3 comes on. If it's deselected (0) I think it's in PFI/VAR Manifold valve mode and the test lamp turns off.

However when in AC Control mode, the E3 output is 'on' regardless of whether 'AC request' is on or off and none of the AC Clutch Control related parameters seem to ever turn it off either.

I think there's a bit more to the logic behind this than I initially assumed....
I wish I could find a wiring schematic for a vehicle that used this PCM as that may reveal some of the secrets....

[dave w]

Perhaps these 1994 Chevy C2500 schematics will help.

94 Chevy C2500 5.7_4L80E_01.jpg

94 Chevy C2500 5.7_4L80E_02.jpg

94 Chevy C2500 5.7_4L80E_03.jpg

94 Chevy C2500 5.7_4L80E_04.jpg

94 Chevy C2500 5.7_4L80E_05.jpg

94 Chevy C2500 5.7_4L80E_06.jpg

[ben73]

Thanks Dave. I hadn't seen any diagrams for a '94 w/4L80e, but it seems they are the same as the other trucks where the only link with the PCM is feedback to indicate the compressor is engaged.
I guess all the 93-5 trucks had a separate and capable AC controller built into the dash and the PCM didn't really need to get involved much...
I might look for some 6 cylinder applications, maybe they used the functionality in the PCM to unload the compressor at high TPS or RPM.

[dave w]

1993 Astro 4.3 CPI

1993 Astro Van 4.3 CPI VIN W _ 01.jpg

1993 Astro Van 4.3 CPI VIN W _ 02.jpg

1993 Astro Van 4.3 CPI VIN W _ 03.jpg

1993 Astro Van 4.3 CPI VIN W _ 04.jpg

1993 Astro Van 4.3 CPI VIN W _ 03.jpg

[ben73]

Thank you!
It's the same with respect to the AC control, but it does use the CPI manifold valve on pin B3 which is interesting.

Because the code has a bit which allows a choice of EITHER A/C control OR the CPI valve, I made the assumption the AC control must use the same pin as the CPI valve (pin B3)... but maybe this is incorrect. There's a bunch of other 'unused' pins on the PCM. I've love to test them all, but an reluctant to risk damaging my spare PCM doing so.

I'll keep hunting. Thanks for your help.

Are there other vehicles that used this family of PCMs other than the C/K trucks? I'm not in the USA so I don't really know what other vehicles may have been available at the time that could have used the same PCMs.

[dave w]

Typically, 1993 ~ 1995 full size Chevy Pickups, Vans, Suburban's along with 4.3 Liter Astro Vans and S10 Pickups with 4L60E transmissions.
There are four PCM part numbers 1993 ~ 1995:
4L60E - 16168625 ($E6) and 16197427 ($OD)
4L80E - 16196395 ($OE) and 16156930 ($31)
Some Full-Size Pickups with Manual transmission - 16196395 ($OE)

[dave w]

Possibly helpful links:

http://www.gearhead-efi.com/Fuel-Inj...Information-31

http://www.gearhead-efi.com/Fuel-Inj...Information-OE

http://www.gearhead-efi.com/Fuel-Inj...Information-0D

http://www.gearhead-efi.com/Fuel-Inj...Information-E6

[ben73]

Thanks Dave. I was aware of all of those except I didn't know the $31 was used in the Hummer. It's different enough that it may actually provide something useful if I can find some PCM pinout info.


I've continued to experiment and know this much:

The ALDL stream has flags for 'AC Requested' and 'AC On'.
'AC Requested is triggered by a 12v input on E12 when the AC clutch is engaged.

If bit 2 at 400F is set to '0', Control of the AC by the PCM is NOT enabled. In this case the ALDL 'AC On' indicates true whenever 'AC Requested' is active.

If bit 2 at 400F is set to '1', Control of the AC by the PCM IS selected.
When this is the case, a number of conditions must be met before 'AC On' will be true. I haven't managed to achieve this as yet, nor do I know which spare pin on the PCM will control the compressor relay.

From the $0D hack, the conditions are:
(values shown are from an application that doesn't use AC control, so may be unrealistic/disabling)

;
;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;-Adaptive A/C clutch control params
;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;
; All timer values are seconds x 10
;
L4010 FCB 0 ;Upper TPS threshold for A/C to come on
L4011 FCB 0 ;Upper TPS threshold for A/C to remain on
;
L4012 FCB 1 ;.1 sec, min time to enable A/C after A/C requested
L4013 FCB 0 ;0 sec, min time to re-enable A/C
L4014 FCB 0 ;0 sec, time delay for A/C to come back on after launch mode
L4015 FCB 0 ;0 sec. time delay for A/C to be disabled if high RPMs
L4016 FCB 0 ;0 sec, min time to re-enable A/C after high rpms
;
L4017 FCB 255 ;6375 RPM, upper rpm limit for A/C to come on
L4018 FCB 254 ;6350 RPM, upper rpm limit for A/C to remain on
;
L4019 FCB 254 ;6350 RPM, upper RPM threshold to disable A/C
;
L401A FCB 254 ;150 deg C, upper cool temp limit for A/C to come on
L401B FCB 253 ;150 deg C, upper cool temp limit for A/C to remain on
;
L401C FCB 0 ;0 MPH, Lower MPH limit for launch mode if A/C on
L401D FCB 0 ;0 MPH, Lower MPH limit for launch mode for A/C to come on
;
L401E FCB 254 ;99.2% TPS, lower TPS limit for launch mode for A/C to come on
L401F FCB 255 ;99.2% TPS, lower TPS limit for launch mode for A/C on
;
L4020 FDB 0000 ;0 sec, min time to re-enable A/C after high TPS
L4022 FDB 0000 ;0 sec, min run time for compressor to come on

This reminds me of when I first installed the '8625 and couldn't figure out how the get it to control a 700r4 TCC despite all the code clearly being there!
I think it took me 3 years of experimentation to finally figure it out!!

I might ask 93V8S10 if he knows anything....
Meanwhile I'll go hunting for $31 Hummer info just in case it holds the secrets. :)

[ben73]

I'm making some progress. Have now found a drawing and confirmed that pin E3 is used for the AC clutch relay control on the 2.2L S10 !

Now to make sense of the prerequisites and parameters to get it to switch the relay.
I have a 2.2 .bin to compare so I may actually get it to work.

[tayto]

Screenshot_20221111-063749.jpg

https://docs.google.com/folder/d/0B9...dh/edit?hl=en#

Wiring Diagrams and Repair Info -> S10 -> 1994

[ben73]

Yes that's the same one I found elsewhere.
Thanks for the link, there's a wealth of handy info there!

[Fast355]

I'm making some progress. Have now found a drawing and confirmed that pin E3 is used for the AC clutch relay control on the 2.2L S10 !

Now to make sense of the prerequisites and parameters to get it to switch the relay.
I have a 2.2 .bin to compare so I may actually get it to work.

From memory the 2.2L also uses a power steering pressure switch. That pin may have to have an input to gain AC clutch control similar to the PCM requiring a +12VDC signal on the brake switch pin to operate any TCC control. I had mine controlling the ac years ago but I forget all the details on how. From memory I think it requires the PS pin in the neutral state meaning how the switch indicates no power steering activity. When you rock the wheels and the pump builds pressure, the signal cuts off the ac clutch.

[ben73]

Hey Fast355, good to see you're still around and have some interest in the old junk :)

I had determined that the 2.2 has a PS switch on pin F8, but I did not know or expect it would play any part in the AC control!
Thanks for your input, I'll experiment with that.

I did have a play with the PS switch input last week, just to see how it works in case it became useful for something else in the future.
I struck a problem in that pin F8 is also used as the 4x4 low range input. Even after I had selected the correct bit to enable the use of a PS switch, the ALDL stream continued to toggle the 4x4 low indication only. Obviously it takes more than just the 'PS switch in use' flag to be ticked to get that input working.
I'll keep working on that if you think it's involved in the AC control.

One question, when you had the PCM doing AC control, were you still in TBI mode or were you running it in PFI mode?


I'll look deeper into this tomorrow. Thanks again for responding.