Jake951

I am troubleshooting a possible DME problem in my '89 951 and I'm looking for another DME to swap in as a check.

What's the difference between DME's in different model year 951's? I understand that 1988 and later use a different DME than earlier years. Is this correct? Do the "non-S" Turbo's use the same DME as the "S" models (except for chip)?

Also, how about interchangeability between DME's of different 944 series cars (944 NA vs 951, etc.)?

Waterguy

The 1988 and later 944T DMEs are identical for the Turbo S and non Turbo S except for chips. These are the part number 915 618 121 08 DMEs with the 28 pin chips. They are also listed as the replacement DMEs for the earlier 1986 and 1987 turbos, so they must be similar in wiring and function. HOWEVER, AFAIK only Danno has made 24 pin chips with the K26#8 maps on them, so you won't be able to swap an ealier (951 618 121 08) DME into your car for diagnosis unless it has the appropriate Guru chips. It would probably work for testing, but have the wrong (LEAN) fuel maps for wide open throttle.

A DME from an N/A will not work. They have different connector assignments as they did not have to deal with the KLR, knock sensor, etc. HTH.

tjbreen

John:

My '87 has a factory rebuilt DME with 28 pin Guru chips that should be compatible with yours. I have forgotten which version of the chips I have but I think it was 9a.

Danno

What's the problem? I've got a spare DME I can send you. Either 24- or 28-pin. I've got one that can use either 24 or 28pin chips. Also have one that can use a 28-series EEPROM as well.

Jake951

The problem was that one day last week out of the blue, the car suddenly started to cut out intermittently while driving. It would idle fine and run perfectly 98% of the time, but every once in a while it would start bucking and the A/F ratio would go dead lean while cruising. I suspected a DME problem.

This past weekend I went through and remade all the electrical connections (harness plug, harness connector splices, O2 sensor plug, etc.) going into the DME, reseated the DME chip into the socket inside the box, etc. and now it's been running fine the last couple days. So I hope it was just a bad electrical connection somewhere and the DME itself is OK.

Danno

"but every once in a while it would start bucking and the A/F ratio would go dead lean while cruising. I suspected a DME problem. "

This would be a sign of a bad speed-sensor. It's the rearward one on the bracket. Without the proper 132-teeth count per-revolution, the DME won't be able to determine the proper duty-cycle to keep the injectors open. Going lean is a sign of this as fewer than 132 triggers are being picked up.

DME problems, they to be more of a start/no-start, run/no-run situation; it either works or it doesn't. Then using force typically flips it between the two states, until sufficient force is applied to keep it in the non-working state permanently...