3.6 swap A/C idle mode

William Miller · 07-08-2007, 12:16 PM

I finished my 3.6 swop about a month ago.
Many have complained about their stalling when using the lightweight flywheel when comming off throttle like at a traffic light.
Mine has not had this issue except once or twice while the engine is going thru the warm up cycles. Not when cold and never once warmed up.

While researching for this project, someone mentioned that the 964 DME has a curcuit to compensate for when the A/C is running.
I think it might eliminate the fuel or ignition cutoff while the engine winds down.

I'm now in the process of getting the A/C working and need further info on the subject. I identified a few wires on the wiring diagram and on the DME harness that have to do with A/C.

Does anyone know how to set this up?
When working on the harness I installed bullet connectors on these wires for future use. (NOW IS THE TIME!)

Any DME or electrical guru's out there?
I have a chart of the pinouts, but don't know what the the wires do.
Seems that all that should be needed is to ground one of the wires and/ or put a 12 volt signal to one to simulate that the 964 A/C system is calling for cooling.

Any help appreciated!

Rouxzy · 07-08-2007, 07:57 PM

It is my understanding that a chip is reprogrammed to make like the a/c is on to compensate for the lighter flywheel. I may be wrong about this but that is how I have understood it to mean. I myself never had a problem with it stalling but I did have a minor issue with it hunting for idle. A Steve Wong chip fixed that along with other benefits.
Tom

Jack Olsen · 07-08-2007, 08:56 PM

Get Steve Wong to burn you a chip with the drop-to-idle programming adjusted. Also, check for vacuum leaks. Their effect (idle hunting) might be exacerbated by the mechanical load from the AC being on.

William Miller · 07-09-2007, 03:08 AM

Thanks for the feedback.
To clarify, it very rarely stalls except for now that I have the a/c under heavy load. When it drops to idle it actually drops below idle for a split second before the idle speed controller (Whatever you call it.) picks it up. With the a/c on there is too much load.
The idle is very smooth and constant once it recovers from the dip.

Jack, There shouldn't be any vacuum leaks because I went over everything before I installed the engine. I'll double check because there is always that possibility.

The DME already has a performance chip (GAIC) that was installed by the PO. I recall trading messages with Steve about this sometime last year and at the time he didn't know much about the A/C idle compensation. I think one of the 3 wires from the DME harness to the car is the key. I think this can be done with what I have without spending money on another chip.
I thought I would check in here before I dig out my wiring diagrams and pour over them.
Does anyone really know their stuff on the DME wiring?

William Miller · 07-14-2007, 04:03 PM

Spent a few days studying the wiring diagram, traded some e-mail with Steve W and spoke breifly to Jim Patrick.
Also trade some PM with Ingo schmitz.
Ingo told me that I wouldn't hurt anything trying to ground or apply +12 volts to the 3 wires that I identified. (He stated it more technically, but in short the inputs are protected some how internally.

Jim Patrick couldn't give me the exact answer off the top of his head, but he did mention that his wiring harness took care of the jumper.

The 91 964 pin-out diagram and wiring diagram shows 3 wires connected to the DME that are AC related.
These are pins 40, 41 and 50.
I believe 40 and 41 are actually outputs providing a ground for the coil on the relays that control the AC compressor and condensor blower.

I think the key is pin 50 and I was right.
Once I applied +12 volts to pin 50 the idle dip went away.
The no load deceleration of the engine acted simularly to the SC (CIS) deceleration valve. rpms fall and slow for a second at arround 2000 rpms and then slowly drop to normal idle of about 800 +-

When letting off the throttle lightly it doesn't cut out the fuel or spark like it used to so cruising is somewhat smoother.

Because the rpm's don't fall off so quickly, my shifts from 1'st to 2nd all of the sudden got smoother.

I'm smiling ear to ear.

Now with the AC on it will no longer stall. The idle bounces once or twice as the idle speed controller catches up. But I can easily live with that.

The 3.6 is running sweeter than ever and now has a few more maners for driving arround town.

Thanks all!