DME computer question

ace_944 · 09:23 AM

Im having starting issues on my 87 944 n/a starter cranks but tachs dont bounce the sensors are installed correctly the wires are fine to the dme computer. My main question is if i messed up and got the small wire that goes on the back of the alternator confused with the one that goes on the starter and tried to start it would that fry my DME computer? Also im getting odd readings at the ref/speed sensors i think only 2/4 of the readings are correct

onspeed · 02-11-2011, 09:49 AM

I don't recall if those wires are connected to the same battery terminal or not. If not, I suppose that would cause some electrical issues... probably blow a bunch of fuses too.

But it sounds like you've got faulty speed/ref sensors...

ace_944 · 02-11-2011, 04:23 PM

Its three wires one goes to starter one to the alternator and one that goes to a connector right by the firewall that goes to the main cabin harness. Didnt even check for a blow fuse thats a good idea but which one would cause no tach bounce? Is there one thats for anything having to do with the 2 sensors? And the sensors are new like i said it shouldnt be anything having to do with adjustment of them it ran fine till whatever happened i didnt touch them since it was running last. I though it was because i pulled the wires to the sensors i little harder than i should have but ive checked the wires since and didnt see anything wrong. Thats why im down to thinking its the dme computer.

HondaDustR · 02-11-2011, 06:21 PM

Do you get voltage to the DME while starting? Maybe the ignition switch is bad.

ace_944 · 02-11-2011, 09:22 PM

I honestly thought my ignition switch was bad but thats only because i was having issues with the starter, if the switch was bad could that make the tachs not bounce? From what ive read and seen it seems like my symptoms have nothing to do with the ignition switch though i could be wrong. It seems like everythings good other than something with the sensors, its really starting to get to me. Any suggestions or input will be greatly appreciated.

ace_944 · 02-12-2011, 07:53 AM

Nevermind i finally got it wires came loose behind the boot of the connector. Thanks for the input guys.

ace_944 · 02-12-2011, 09:25 AM

OK new problem how the heck do you get the wire pins out of the connector?

HondaDustR · 02-12-2011, 02:22 PM

Which connector? Usually there's a little protruding tab pointing back towards the wires that engages a slot or the inside edge of the connector block. Usually you have to poke it in with a pin or a small jeweler's screwdriver to allow the pin to slide out. Some connectors actually have special release tools, but I don't know if there is anything like that for the connectors on these cars.

ace_944 · 02-12-2011, 05:59 PM

I was talking about the speed/refrence sensors but i just ordered the new harness from LR so thats all takin car of. After looking at all the options i figured it was the best bet. Thanks again for all the input guys.

ace_944 · 05:29 PM

Ok i got the new harness installed it and still no start im pretty sure i put it in right but i did get a little confused when it came to the grounds in the walk through it doesnt really give a good description of where your supposed to install them especially because they tell you to leave in the o2 sensor ground. I would start suspecting something else but im getting odd readings off the terminals one of the terminals shows 156 kilohms on both sets of pins which is waaayyyy out of spec. Any input would be more than welcome.

ace_944 · 02-16-2011, 08:32 AM

Does anyone know where the ground pins go on the LR harness? As of now i just have them going to where they originally came from, yes i ripped out the o2 sensor ground and soldered it to the bare ground wire nothing else seemed to make sense.

ace_944 · 12:50 PM

I think i might have fried my dme computer this would explain why im getting such odd readings. I opened it up separated the circuit boards and started looking around. I see more that one spot that has what looks almost like rust on resistors and a few other components would this mean its fried or is that just normal corrosion from moister? Whats my best option? Is it possible to repair these thing at home or is that suicide?

ace_944 · 02-16-2011, 02:00 PM

ace_944 · 02-16-2011, 03:22 PM

Fried dme it became very obvious once i completely took apart the dme it fried off the coating of the circuit board there was more than one spot that had copper showing. Im pretty sure the cause was water damage from the battery box leaking. Anyone have a spare dme comp for a 87 944 laying around?

Guess its off to the part forums.

HondaDustR · 02-16-2011, 03:56 PM

That sucks. You shouldn't have too much trouble finding another one. Mounting it under the dash below the steering column like in the early cars made so much sense. I wonder what made Porsche want to change it, except that they seem to just like mounting things in remote, weird places that are a PITA to deal with.

ace_944 · 02-16-2011, 04:27 PM

Yea hopefully things will go smoothly this is my only car so ive been hurting without it for about the past week and hopefully im right about the water damage cause if its not and i fry another one ill pretty much be passed my breaking point.

HondaDustR · 08:29 PM

Quote:

Originally Posted by ace_944

Yea hopefully things will go smoothly this is my only car so ive been hurting without it for about the past week and hopefully im right about the water damage cause if its not and i fry another one ill pretty much be passed my breaking point.

Yep, BTDT...for 3 months last fall trying to go to work, school, and rebuild an engine for the first time all at once, all while always trying to figure out how to get to first two activities. Preview of hell, but in the end it's all worth it. No other car is quite the same. I would do it all again to keep her on the road.

If it were me, I'd look over some wiring diagrams carefully to make sure everything's hooked up right in the mean time. As for the grounds, there is the ground stud on the bellhousing that the main battery ground connects to, as well as at least one more main ground from the fuse block. I think there might have been another smaller stud in the same area that had more ground terminals, but I can't remember. Either way, that area is where the DME gets its ground IIRC. Ultimately, a ground is a ground, as they are all connected. The O2 sensor gets its signal ground through the exhaust system, but the heater (two white wires) does not. I don't know where it gets its ground or supply, but it cant be too hard to track it down. This diagram may come in handy to double check everything.
DME Connector 35-pin
The DME connector housing can be removed by removing the small screw and sliding it off. The it makes it easy to see the wire colors and be able to stick multimeter probes alongside the contacts from the back for testing, especially with the DME plugged in and running. The other nice thing is the arbitrary pin numbers on sensors and other engine control devices that are often referenced in clark's garage, the factory manual, and sometimes stamped on the connectors themselves actually correspond to their respective pin numbers in the DME plug diagram.