Peteinjp

This is what I was trying to say in post 12. You just have to dig in and go at it methodically. If you have questions like- “what does this in the wiring diagram mean?” You can probably get useful answers.

It’s a pain for sure. Here is a great primer on how to read the diagrams if you find them as confusing as I do.

http://www.928-electrics.com/Docs1/P...WDP%20Only.pdf

LM964

Agree. This download is really useful. Explains so many niggling questions I have when tracing faults and component connections.

orange911

Did you ever get this sorted?

porsche964IRE

No I am still not fixed
Will have a go with the wiring diagrams this weekend.
Thanks everyone for the help.
I have to figure out why the DME is only get 8/9V while ignition is on, So will chase the ignition DME wires or at least try.
The terminal X arrived and did not make any changes. Car is going in for refurb later in the month so would ideally have sorted by then.

ZG862

I've been doing some similar troubleshooting (my current problem seems to be fuel pump, so not the same as yours) which led me to trace the DME wires.
This involved pulling the Central Electrics board out of it's tub to get access to the big bad plugs on it's reverse. Note that there is a moulded plastic lock rail that retains all the plugs. If you want to pull the plugs, this tab must be slid back around 10mm. Do remember to pull the battery terminals before poking around here as there are plenty of live circuits. See sheets 5 and 11 of the wiring diagrams for much of this.

The positive terminal on the DME should be marked 30 on the relay unit and 3 on the central electrics unit DME socket (Relay 41). This socket connects to the "E" plug on the underside of the CE board to terminal E31 (i.e. 3rd column, 1st row).
E31 connects via a red 4mm loop wire across the back of the plug to E35.
E35 connects within the CE board (i.e. via the copper tracks) to G25. It also branches off to E25, which connects back to E21 via a 1.5mm red wire.
G25 connects directly to the battery via 4mm red.
E21 connects within the CE board to fuse 35 - the DME fuse. (also connects to D21 which I hadn't noticed before, though this seems to be unused).

Therefore if you have continuity between each of these points, I (as a DIY electrician with limited skills) can only put your low voltage down to poor earthing on your meter probe, a problem within the DME relay itself, or an issue within the DME control unit. Between which connections are you measuring the 8/9V?

Z

bd111

are you based in ireland? If you are I know the right Porsche guy to take a look at it

porsche964IRE

Yes I am.
is that DOB?
My problem is someone will have to come out to fix it.

bd111

chat with terry Jackson. I’ve done work on my 964 with Terry and his son George. Absolute gentlemen and pros. They specialise in classic Porsche and mercs. Can’t imagine they’ll go out to you, but I’m guessing they could arrange a tow or you could. That’s their website http://terryjackson.ie/

porsche964IRE

Update.
Still not fixed, today when I went to it the battery was low, however the DME worked perfectly, did the same again later. But when I put battery charger/jumper on the battery the DME stopped working as it should.
I jumped a new wire from Pin 86 to battery positive for test purposes which the DME works as it should but of course this is not a fix, I must run a new wire from pin and attach it to a fused ignition plug. Any suggestions?
Or reading a different rennlist forum could my problem be a poor ignition switch? https://rennlist.com/forums/964-foru...ng-else-2.html

Ralph3.

I replaced mine couple of years ago, it solved a strange issue with my headlights. A fairly inexpensive item to replace, I noticed when I jiggled my key the lights would go on and off.

systemsc

View and understand the Porsche diagram in post #30, i.e. it's all there with regard to the DME relay. Avoid guessing.

porsche964IRE

After spending lots of money on "genius" mechanics I give up on mechanics, €150/hour labour for the guessing and looking into a hole.
I am not leaving my pride and joy in anymore "geniuses" yards for them to be poking around the wiring and leaving it outside.

I have decided to fix it in the following way and would like advice, I will cut and run a new wire to DME pin 86 from the back of ignition. I would like to know which wire I can join onto at the back of ignition to insure the DME gets full 12v when the ignition is on and none when off.

Or could I join wire from pin 86 to a fuse wire and piggy back off existing loom without needing to enter cabin like radio etc.

Thanks.

porsche964IRE

Have I any suggestions on what wire to connect to? Maybe test continuity for a wire heading from terminal X?

ras62

Did you fit a new crank sensor? If not I am sure it will solve your issue. I fthe car is still on the old type sensor you may need a holding bracket and a change of plug on the wiring. If it uses the later 996 sensor its an easy swap with the car on a lift.

porsche964IRE

Solved

After a long time of self diagnosis and misdirection from mechanics I stuck with my incline of immobiliser fault, after a long time of figuring out the wires and diagrams I removed the immobiliser function to original and no issues since, all working perfectly.