DME relay failure? Symptoms?

JohnS_77 · 04-12-2005, 08:00 AM

What are the "normal" symptoms of a failed DME relay?
This weekend I installed a remanufactured alternator in our 85 Targa. After I finished the install Sunday afternoon, we took the car out to meet up with from friends about 5 miles from home. It ran great there and back home. Less then a half hour later we ran up to a town about 30 minutes away from home. It ran great on the way there. It started great when we were ready to go home. Leaving town the speed limit changes from 30 MPH to 45 MPH. As we were accelerating out of town the car cut out. It was just like somebody turned off a switch. The car fired right up when we tried to restart it, and it ran great all the way back home.
Monday morning the car stalled in the driveway when my wife was leaving for work. It restarted and ran great on her way in. At 5pm when it was time to go home, the car would not start. It turns over, but won’t fire. I think it is getting gas. When I got there my wife hit the key and I could smell gas when it turns over.
I didn’t have any tools with me, so I could not pull a plug. By smelling gas I assume the engine is getting gas, perhaps it is not getting spark.
Does this sound like a DME relay failure? We had the car flat bedded to the shop. The shop has something like a two week backlog. I was wondering if I ordered a new DME relay and ran up to the shop and installed it, if the car would start? At least then we wouldn’t be without the car for two weeks.
Or did I knock loose a sensor or something when I had the car apart, and it just took a couple miles to disconnect itself?

Thanks in advance for any help.
John
1985 911 Carrera Targa

Rot 911 · 04-12-2005, 08:02 AM

If you can smell gas it ain't the DME relay as that is also the fuel pump relay.

cellison · 04-12-2005, 08:14 AM

I changed the DME relay on my 88 in December. Car would not start on occaision, either hot or cold, and actually cut on me once shifting from 2 to 3rd. when troubleshooting, can't remember if the fuel pump was working, but pulled the old DME out and checekd it. It looked good, but for $38 and being 18 years old I decided to change it. Have not had problems since.

Charles
88 cab

Charles
88 Cab

Crowbob · 04-12-2005, 08:19 AM

I'd check the coil. If it's original, it may have burned out. When they go, they shut down intermittently. However, they act worse when warm for some reason.

JohnS_77 · 04-12-2005, 10:01 AM

I feel like a tool for sending it directly to the shop. I should have had it dropped off at my house.

scottb · 04-12-2005, 10:21 AM

If the relay has never been changed, you might as well start there.

JR911 · 04-12-2005, 10:56 AM

John,

I had just about the same symptoms with my 86 as you described.

After driving a while, ( up to 3+ hours) the car would not start or if driving the engine would shut down, as if you tuned off the key.

One time on the freeway the car quit on me three times. Each time I wiggled the connector on the DME where it plugs into the relay. After a few min. the car would start, run normal a few miles then quit again. I limped home where I promptly removed the relay and took it apart.

It was the original one (85) and after closer inspection MANY of the solder points on the circuit board were broken. I re-soldered the joints, installed the relay and the car has been running fine since. I have put a few hundred miles on the car since the solder repair. I will be buying a new relay and keeping the old one as my spare.

Check for a post with pics from Steve Wong a year or so ago on this repair.

Hope this helps you, let us know!

88911coupe · 04-12-2005, 12:37 PM

Same symptons on my '88 and as with JR911 it was a broken solder. This was very hard to see but once I found it it was a piece of cake to fix. It's worked fine ever since and that's been about 2 years.

Wil Ferch · 04-12-2005, 12:40 PM

Once you fix this....you may want to place a small block of foam rubber under the relay.

Why?

The relay is plugged in sideways...and the "cantilever" load as it just hangs sideways in space....IMHO....contributes to the solder failure. A rubber block below "supports" the relay and lessens the strain on the soldered connections....

Wil

Crowbob · 04-12-2005, 12:46 PM

Listen to Wil and learn.

Steve87-911 · Steve87-911's Garage

Quote:

Originally posted by cellison
... It looked good, but for $38 and being 18 years old I decided to change it. Have not had problems since.

Wow. 18 years is a long time for the DME relay to last, yes?

htron435 · htron435's Garage

If the new DME relay doesn't fix it, check your fuel pump pressure. You could have a weak or dying fuel pump. Another place to look may be the cylinder head temperature sensor.

strupgolf · 04-12-2005, 06:21 PM

Maybe Im off base, but where can I buy a new DME chip?

htron435 · htron435's Garage

Our host probably stocks them, but if not, I think that every Porsche dealer keeps them in stock.

Paul Franssen · Paul Franssen's Garage

John, the way you described it, is exactly like a DME relay failure, except for smelling gas. (but that may be "spurious" info)
... My 88 relay gave up the ghost just driving on the freeway: one moment the car ran, then there was an cutout, then some intermittant cutouts, then the engine hiccupped a few times, then it stopped. And restarted, and later stopped again. ON and OFF kinda thing. Put in a new DME (after having been -illegally- towed home...), we have ON. And it's stayed there since. I have an extra relay in my glove compartment.

cellison · 04-13-2005, 05:35 AM

I got the April copy of Panorama yesterday, and in the tech Q/A section page 77, someone wrote about their 3.2 acting the same way. Sorry I can't cut and paste and can't spend time typing in hte whole letter and response, but it points to the DME relay and/or the cylinder head temp sensor.

Yes my relay was 18 y/o and looked ok, but my eyes aren't what they used to be.

charles
88 Cab