Car Forum / Porsche / Porshe 944 / February 2004
Help - Need DME Connections
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Reno - 10 Feb 2004 17:52 GMT Help - Need DME Connections
I have a 1987, 944 NA with a no start, no fuel problem. I'm sure I blew something in my computer. I managed to turn a simple problem in to a huge problem.
Background: Car would not start. No spark, no fuel. I checked out my DME relay and it is good. Turned out to be "no voltage" at pin #86 of the DME socket (with ignition switch turned on). I removed the DME relay cover and jammed the main relay closed with a tooth pick and the car started right up. By closing the main relay contacts, battery voltage was then sent to DME wich in turn closed the fule pump relay and energized the fuel pump. I suspected the ingnition switch went bad (unlikely since every thing else worked fine) or the wire going to pin #86 of the DME relay socket may have slipped down thus not making contact with the relay. All I have is a haynes manual and it shows a green/red wire going from DME relay socket pin #86 to the compressor. (?) Could this be right?
Now it gets worse. In an attempt to check the connections on the bottom of the DME relay socket, I attempted to lift the fuse board up to look underneath. I was in too much of a hurry to disconnect the battery and DME. (If you find yourself in a hole, stop digging). No luck, too hard to pull the board up far enough to work with. Now, not only do I not have power at pin #86, but the tooth pick trick doesn't energize the fuel pump relay anymore. Jumping from battery voltage (pin #30) to DME/Fuel Rail (pin #87) and Fuel Pump (pin #87b) powers the fuel pump but not the injectors. Apparently DME is not sending signal to pin #85b of DME Relay. I still have spark, but no fuel. Fuel pressure is approx 39 psi upon cranking, but injectors aren't working. I think I blew something in the DME. I have the great schematics of the DME form FRWILKS, but don't know all the connections to the 35 pins of the DME.
Just so we don't get off track, Fuel pressure regulator and damper are good. My DME Relay and spare relay are good. Speed and Refernce marks sensors are good. Coil and wires are good (I have spark). I am in the process of checking/replacing ignition switch in case it feeds pin #86 of DME relay, but I don't think so.
Was all this too much? Just wanted to document in case anyone else had same problem. I know 944 no start problems are a royal pain. I've had 3 no start problem. First was bad fuel pressure regulator that shut down computer. Problem pin pointed by disconnecting on injector, reduce injector current draw. Second was bad solder joint in computer. Resoldered board, worked fine. By the was I have really abused the computer and now I finally broke it. Third was no ignition power to working DME Relay, still trying to work it out.
Forget everything above and please let me know if you have answers to the following 3 questions.
Questions:
1. Does anyone have a list of the connections to the 35 pins of the DME? What sensor/relay goes where?
2. Where does pin #86 of DME RELAY get its power from? What color wire to where?
3. Where do pins #87 and #85b from the DME RELAY end up at the DME connector? Need to identify possible problem in associated circuit of the DME.
Thanks
Reno
Paul Sure - 10 Feb 2004 23:18 GMT I tried to send you the schematic from the work shop manual that has the pin connections but the email bounced
Paul
Reno - 11 Feb 2004 02:05 GMT Paul
Sorry about email address, don't like spammers. I'm at biznet19@att.net.
Anyway, I have schematics for the computer, but they don't show what external relays and sensors are connected to what on the 35 pins of the computer.
The second stage of the DME relay (fuel pump relay) is not being energized by the DME. I'm trying to figure out were pins #85b and #87 of the fuel pump relay end up on the DME connector. Then with the schematics that I have, I can test computer components.
Thanks Reno
> I tried to send you the schematic from the work shop manual that has the pin > connections but the email bounced > > Paul Martin? - 11 Feb 2004 02:45 GMT The DME computer GROUNDS pin 85 of the DME relay WHEN the engine starts cranking. The relay takes power from pin 30, always on. If your DME doesn't ground pin 85, you can take out the relay, connect pins 87 and 87b and connect them by wire to a fuse switched on by ignition circuit (e.g. auto tranny, even on manual). The DME computer can be repaired, contact F R Wilks or Don Istook via rennlist.org forum. Regards, Martin
Reno - 13 Feb 2004 00:54 GMT I don't believe this is accurate. Pin 85 is always grounded and does not go through the DME. Pin 85 is the ground for the main relay that is activate when power is applied to Pin 86 by the ignition switch. The main relay supplies power to the DME and Fuel Rail. The DME then grounds pin 85b which activates the fuel pump relay and powers the fuel pump.
My question is, if you can't get ignition power to pin 86 and it IS NOT the ignition switch, were would the fault be?
> The DME computer GROUNDS pin 85 of the DME relay WHEN the engine starts > cranking. [quoted text clipped - 6 lines] > Regards, > Martin Martin? - 13 Feb 2004 01:47 GMT My post is correct. The whole point of the DME relay is to switch off the fuel pump in when the engine stops for fire safety reasons i.e. in a crash. Therefore the DME computer (switched on via ignition key) detects from the engine speed sensor when it is turning then uses a transistor to ground pin 85 which triggers the relay, which then powers the fuel pump and (87b) idle stabilizer circuit and the O2 sensor. I suggest you by-pass the relay as I previously described, and is you have spark the car should start and run normally. Regards, Martin
Reno - 13 Feb 2004 01:58 GMT Ok. When I jump from Pin 30 to 87b and 87, car starts and runs fine. When I put the DME relay back in, no start. I have checked out the relay and my spare relay, both work fine. I just can't get voltage to pin 86. Replace ignition switch, still no power between pin 86 and ground. Any ideas?
> My post is correct. The whole point of the DME relay is to switch off the > fuel pump in when the engine stops for fire safety reasons i.e. in a crash. [quoted text clipped - 6 lines] > Regards, > Martin DCorley - 13 Feb 2004 06:11 GMT do you have the wiring diagrams for your car, they go a long way towards tracing issues....
> Ok. When I jump from Pin 30 to 87b and 87, car starts and runs fine. When I > put the DME relay back in, no start. I have checked out the relay and my [quoted text clipped - 20 lines] >>Regards, >>Martin Reno - 13 Feb 2004 17:27 GMT Up until now I was trying to use that worthless Haynes manual. One of the guys in this group was kind enough to send me a couple of pages out of the porsche manual. Just waiting to hook up with a friend who has the program to open the files.
> do you have the wiring diagrams for your car, they go a long way > towards tracing issues.... [quoted text clipped - 23 lines] > >>Regards, > >>Martin DCorley - 14 Feb 2004 01:05 GMT if they are PDF files, you can download the reader for free from www.adobe.com you want Acrobat Reader ...
> Up until now I was trying to use that worthless Haynes manual. One of the > guys in this group was kind enough to send me a couple of pages out of the [quoted text clipped - 46 lines] >>>>Regards, >>>>Martin Paul Sure - 14 Feb 2004 13:29 GMT I made them in PS format so you can send them directly to a postscript capable printer. Or get ghostview (free) and view the pages on the screen.
Paul
85 must somehow be connected with ground and 86 need to get a +12V from somewhere. Does your car has a anti theft installation?
Reno - 14 Feb 2004 22:58 GMT FIXED!!!!
You don't need to be an auto mechanic to work on a 944, just a computer tech and electrician.
I appreciate all of your inputs, gave me ideas for trouble shooting. Paul, Thanks for the pages.
I now know pin 86 of the DME relay comes out of the fuse/relay pannel as a black/yellow wire from E32 (that's E block of wires, row 3, second pin). The wire then goes back into the fuse pannel at E44 (Yes, E block, forth row, forth wire). Then comes out of fuse pannel again at F14 as green wire and goes to alarm. In my case I don't have a factory installed alarm, so the green wire is connected to the black/white wire that powers the alarm from ignition switch #15 (ignition switch on).
After much troubleshooting, found power in green wire from alarm but not the black/yellow wire that came out of and back into the fuse pannel. So took the fuse pannel apart. What a job. Seven laters of contacts and copper buses. Cleaned everything up and put it back together. Now have ignition power to DME relay. Car starts right up.
BTW, the computer is pretty tough. I took it out and put in in a few times without disconnecting battery. Shorted some circuits. Even resoldered the board twice. And it still keeps on ticking.
Again, thanks to all. When you're stuck, every idea helps in troubleshooting.
Reno
> I made them in PS format so you can send them directly to a postscript > capable printer. Or get ghostview (free) and view the pages on the screen. [quoted text clipped - 3 lines] > 85 must somehow be connected with ground and 86 need to get a +12V from > somewhere. Does your car has a anti theft installation? Martin? - 14 Feb 2004 01:40 GMT Reno, exactly as I thought, you have the same problem as I have, your DME computer doesn't ground pin 85 when the engine starts cranking. You have three choices. 1. Wire pins 87 and 87b to the auto tranny fuse (or any that is switched on with ignition) and live with it, as I do. 2. Repair the DME computer, it' just question of replacing a transistor, (once you have found it !). 3. Get replacement DME, possibly an exchange one from Bosh. Regards, Martin
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