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Porsche Crest not starting! dme?

Ok, I'm driving home last night (it's raining). I get home and park the car. About a minute later I figure I should move it. I go to start it and nothing. It just turns over. This morning I go out and try it again, nothing. My dad and I are looking at it and it is not getting spark. The coil is getting power and it tests good, but it is not sending power to the distributor, the green wire is not grounding itself in the DME... Is there some type if test to check this or something else that might be wrong? Anyone have any ideas? By the way how much does FRwilk charge for a dme rebuild?
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'83 arctic silver 944 n/a
Power steering? who needs it!
Old 05-02-2003, 09:28 AM
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Old sparK plug wires? You check the wire from the coil to the dis? No corrosion or anything?
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Old 05-02-2003, 09:52 AM
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Yeah the wires are pretty old, they seem fine. But the coil isn't making ground. And would the wire really all of a sudden go bad, I mean the car sitting for 30 seconds?
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'83 arctic silver 944 n/a
Power steering? who needs it!
Old 05-02-2003, 10:16 AM
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what is it with all these 'early' 944 'no spark' problems lately...it's worse then SARS

easy way to check your coil...

pull the Hi Voltage lead out of the distributor and keep it away from any other wires, i.e. injectors...else you will blow that DME

get the ol' cheater wire out...that is, connect a wire to ground & tap away on that green wire to see if you get spark from the HV lead to chassis/engine...hold about 1/16th inch away...and tap the ground to that green lead's terminal

I still can't figure out how a reference sensor 'wears' out, but that would be my first guess, before a bad coil or a bad DME. If you got a volt/ohm meter the sensor should read around 900 to 1000 ohms.

and even if it does I wouldn't be convinced it's doing a good job of pulsing the DME (which then sends a 'ground' pulse out on that green wire to the coil). make sure ALL connections are cleaned up & shiny too...from the sensor, the DME, the coil, the starter, the battery terminals...both...and all those red wires to the + terminal...yadda..yadda..
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Early '85 944

Last edited by carsontc; 05-02-2003 at 12:18 PM..
Old 05-02-2003, 12:16 PM
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Does your battery box leak onto your passenger side footwell?
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Old 05-02-2003, 12:37 PM
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Quote:
pull the Hi Voltage lead out of the distributor and keep it away from any other wires, i.e. injectors...else you will blow that DME get the ol' cheater wire out...that is, connect a wire to ground & tap away on that green wire to see if you get spark from the HV lead to chassis/engine...hold about 1/16th inch away...and tap the ground to that green lead's terminal
This is to check if the coil is good right? We checked it with a volt meter, it's good.

And, no my battery box doesn't leak. That doesn't matter though because I don't know if it's pre 85.5 or just the 83, but the DME is under the steering column...
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Old 05-02-2003, 04:29 PM
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all the pre 85.5 or 'early' 944 use the same DME part and yeah, it's under the steering column

ok, you have a volt/ohmmeter...good

and you said you have 'no spark'

but you do have +12vdc on the small black wire of the ignition coil...good. btw, the +12v comes from the key switch which also sends it to the 'DNE'/fuel pump relay

(btw, you do hear the fuel pump? just curious, as that fuel pump relay shouldn't effect the 'no spark' problem anyway)

and we know that with the key 'on' you should have +12v on the green wire terminal of the coil too...simply because it is feeding thru the coil winding from the black wire

but the ground 'pulsing' from pin 1 of the DME via that green wire to the coil is not there when you try to start it

before you replace the DME, the most expensive part on the check list, you may want to eliminate the more common problems

like I mentioned earlier...make sure ALL electrical connections are clean...from the reference sensor, the DME, the coil, the starter, both the battery terminals and all those red wires to the + terminal...get a large tube Permatex dielectric 'tune-up' grease...

clean & coat all this stuff and do this cause it needs to be done every 10 years and probably hasn't been done in 20 years...you may need to use sand paper or a toothbrush sized wire brush to clean the oxidation off and get everything 'shiny'

check inside distributor cap & make sure the rotor is on tight...it is held in place with a small screw..again, tune-up grease...all the spark plug wiring needs this tune-up treatment too

even if it doesn't fix the 'no spark' problem it will prevent a few dozen new ones that will very likely come up...look around, how many 20 year old cars are around your area?

as for the reference sensor...the connector has 3 pins, 1 of the outside pins is a shield and from it to either of the other 2 pins (with the ohmeter) should read 'open'

measuring the resistance between the middle and remaining pin should read around 900 ohms to 1100 ohms. (btw...we have tested these as 'good' and still had problems 'til we replaced the sensor.)

to find the reference sensor look at:

http://www.clarks-garage.com/shop-manual/ign-02.htm

I would open the reference sensor plug/connector at that 'feed-thru' bracket near the firewall to measure this

also with your volt meter set to low low scale, you may be able to read a small AC voltage (~2vac spike) when cranking

let us know what you come up with
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Early '85 944

Last edited by carsontc; 05-02-2003 at 09:30 PM..
Old 05-02-2003, 09:25 PM
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Man, you guys do things the hard way. One side of the coil gets batt. voltage from (you guessed it) the batt. all the time. The other wire on the coil gets voltage (batt.) when you turn the ign. on. A simple volt metere is all you need. Is there 12v when you turn the key on? If yes, proceed, if not, you probably have a grounded wire. now then, most multi meters have a rpm function. Hook it up to the secondary hot wire and try to start it. If you have an RPM reading, you're getting ing. pulse. something's wrong with your dist./rotor/wires/plugs. If no rpm sigal, then your TDC sensor is mess up, or your pin is gone or something along those lines. DME's rarely, rarely go bad. My first diagnoses would be vapor inside your dist. cap condensed and now you are just not getting that spark. clean the inside of your dist. make sure rotor is bolted on tightly.
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Old 05-02-2003, 09:50 PM
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a neat trick I picked up on accident: If you take your rpm sensor out of bracket, but leave it hooked up you can move a piece of metal by it a few times (like a bicycle spedo works) and you should hear the fuel pump spurt. OR I found that if you hold the end of the sensor over the O/I switch of one of the flourescent portable shop lights, it' will pickup the pulse from the light and activate the fuel pump.
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Old 05-02-2003, 10:03 PM
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Porsche Crest

SHE RUNS! Thanks for all of the suggestions guys. We tried what you all said and what we found in the factory manual. The problem ended up being the connectors on the back of the engine for the sensors on the flywheel. They were loose and the pieces of plastic were broken that held them together. We put some tie-raps on them to hold them together. I'll go get some of that "tune up" grease.
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Power steering? who needs it!
Old 05-04-2003, 02:47 PM
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cool

gotta make sure ALL electrical connections are good and clean on these old cars
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Early '85 944
Old 05-04-2003, 07:13 PM
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