Use of a 944 DME in 84 3.2L Carrera

[ausgezeichnet]

I've read that DME's from a 85.5 and later 944 have been used in Carreras. Can the DME be use as is (other than the chip replacement) or do other mods need to be made to it? Also, does the 944 DME take a 24 pin or 28 pin chip? Thanks.

[ChrisBennet]

From memory, the 944 DME hack involves changing a precision resistor in the injector driver circuit and changing it from 24 pin to 28 pin EPROM.
Not that you asked, but you'd be better off fixing your own DME if it's broken.
-Chris

[ausgezeichnet]

Thanks. I was just looking for a spare DME for testing to make sure my original is indeed bad. All the cyclinders on the right bank stopped firing which leads me to believe the signal from the DME for the fuel injectors for that side may be bad. Amazing how it runs on only 3 cylinders.

[Lorenfb]

"All the cyclinders on the right bank stopped firing which leads me to believe the signal from the DME for the fuel injectors for that side may be bad. Amazing how it runs on only 3 cylinders."

Not true! The 3.2 DME has ALL injectors connected to a common point in the
DME.

[ausgezeichnet]

Loren,

Do you know why there are 2 separate pin assignments for the left and right bank in the ECM that control the injection time signal. According to the DME fuel injection diagram in my Bentley manual (page 240-38) they never come to common point. Am I missing something? Thanks for your help.

[Lorenfb]

That design (2 separate wires) reduces the current requirement of each wire
and thus reduces the wire size, i.e. voltage drops when pulsing the injectors.

[ausgezeichnet]

Loren,

Ok. That makes sense. So could a bad output from either terminal 14 or 15 in the DME in this design cause one bank of cylinders not to fire? Thanks.

-Mike

[Lorenfb]

Yes, but only if the circuit board in burned near pins 14 & 15, rarely happens.
Most likely the injectors don't have +12 volts on the "dead" side,
or the common return line to 14/15 is broken.

1. Remove one injector on the dead side and check for +12 volts
using a test light.
2. Check continuity of the injector wiires.