Carrera DME unit question...

[ChrisBennet]

With an Eprom emulator setup you can "tune" without opening the box and changing chips. Take a run, look at your A/F curve and/or power, adjust the maps and take another run. You wouldn't do this while underway.
-Chris

[silverc4s]

Chris, et al;

Agreed. I guess I took Dutchie too literally... didn't mean to hijack the thread...sorry.

[stlrj]

Richard,

The 87 control unit is not interchangeable with the 85 because the wiring harnesses are different. I already had this discussion with my P-wrench.

Regs,

Joe

[ChrisBennet]

Originally posted by stlrj
Richard,

The 87 control unit is not interchangeable with the 85 because the wiring harnesses are different. I already had this discussion with my P-wrench.

Regs,

Joe

Your wrench is quite mistaken.
-Chris

[stlrj]

Chris,

I verified the differences looking in my Haynes wiring diagrams. They don't seem to be pinned the same.

Regs,

Joe

[ChrisBennet]

Originally posted by stlrj
Chris,

I verified the differences looking in my Haynes wiring diagrams. Looks like they are pinned differently.

Regs,

Joe

Joe,
Do you rember which pins? I run my '89 motor in my '86 911 with an '86 DME without any problems. When I tried the '89 DME the motor ran but not great so I assume(d) that my '89 DME had some problems. Perhaps there is a harness difference.
-Chris

[stlrj]

Chris,

I have a late production 86 3.2 that came with the 87 control unit. That's how I found out that that the early ones would not interchange when it came to smog time...it failed because the timing was too far advanced. That's when we found out that the factory started using the 87 engine on some late production 86's. The referee station had to modify their data after I proved to them of this fact.


Regs,

Joe

[ChrisBennet]

stlrj,
Yes, the timing advance is slightly different and the idle is 880 on the later DME's instead of 800rpm. (See earlier posts in this thread.) I don't understand how that would effect smog exactly. I'm curious, what does the sticker in your engine compartment say the idle should be?
-Chris

[Tim Polzin]

Joe:

The pin-out difference is news to me. Do you know which pins were different? The only difference I remember seeing on DME harnesses was a different plug for the O2 sensor.

Tim

[RickM]

Here's an informative link on '84 - '89 DMEs.

http://members.rennlist.com/messinwith911s/DMEHacking.htm

[Wil Ferch]

Chris is right:
I have an acquaintance who ( surprisingly, we find) runs a late DME box on his USA spec '85 Carrera....ended up having to buy a 28 pin custom chip instead of the normal 24 pin chip his car should have.
--- no problems----- the box fits and his car runs...empirical evidence prevails.
---Wil Ferch

[stlrj]

Chris,

No sticker since the engine came from an 86 wreck.

Joe

[Tim Polzin]

I just checked my Haynes Manual (not sure if there is an update) and their diagrams only include the 84 and 85 model years. I did find what I think is an error in the Bentley manual. From 84 through 87, they show DME pin 21 (BLK/VIO) going to one lead of the tach and DME pin 4 (YEL) going to the ignition, where on the 88 through 89 diagram, they show pin 4 going to the tach and pin 21 going to the ignition switch. I believe this is an error in the manual and not actually a physical change. This might be what Joe was refering to.

Tim

[ChrisBennet]

Originally posted by Tim Polzin
I just checked my Haynes Manual (not sure if there is an update) and their diagrams only include the 84 and 85 model years. I did find what I think is an error in the Bentley manual. From 84 through 87, they show DME pin 21 (BLK/VIO) going to one lead of the tach and DME pin 4 (YEL) going to the ignition, where on the 88 through 89 diagram, they show pin 4 going to the tach and pin 21 going to the ignition switch. I believe this is an error in the manual and not actually a physical change. This might be what Joe was refering to.

Tim

I just checked the factory manual schematics and pin 21 goes to the tach, at least it does for 1985, 1986, 1987.
I looked at 1988 and 1989 but frankly I couldn't decipher them. The '88 and '89 seem to have a lot more stuff hung off that pin.
-Chris