DME Relay Questions
 

Have a few DME relay questions below. My 1993 911 (964) has a reocurring problem of a failing DM relay. The car will run fine for a few months and then start to skip. After replacing the DME relay this takes care of the problem but I'm going through around 2 relays a year. A few question below.

1. Is it normal for this relay to only last about six months?
2. Is there one brand better than another. I usually buy from our host pelican.
3. Can these be repaired ( I have a small collection of these relays now)
4. Is something else in the system causing this relay to fail?

No, it's not normal for these relays to fail so soon. Do you have any problem with the other relays, or just with the DME relay? If you have other problems, then I would check the charging voltage. But, if just this relay is failing, I would look for bad connections in the circuit or at the relay itself. I suspect that it's drawing too much current and overheating. I don't think that there is any problem with the quality of the replacements. Also, I would check all the ground connections. A dirty or corroded ground could cause this problem.

Had a similar problem, the DME relay was a symptom not the cause.
Start by checking voltage at battery, at rest and running.
Then start tracing backward to Alternator to Battery.
Then DME CU to alternator.
There are a bunch of ground points, some are mult- stacked.
Need to take these apart and clean them. There is a diagram in Streather book and shop manuals showing location - something like 16 ground points!
I actually had a power wire from DME CU to Alternator that was bent over like a paperclip inside the wire harness, that over time, had caused resistance to draw. Could see the burn mark at the kink in wire.

As far as brands go, specify " factory DME relay" the aftermarkets are crap. Actually, even those labeled "OEM" are crap. I had three, all in new boxes, and all failed.
The solder joints are weak. Steve Weiner/ Rennsport /Systems resolders all his before sending them out- they are that unreliable. So don't discount that possibility.

Hope this helps

Sometimes there's a different manufacturing issue.

Nope. The original relay in my car is going into its 19th year. It did fail a few years back, but after I repaired it, it is as good as new...actually better.

I never had or bought a non-original relay, so I can't comment.

Yes and very easily. First, determine what in your relay has failed.

Start by removing the cover and checking the contacts. They should not be pitted due to arcing. Mine looked like new after 16 years; no pitting or wear whatsoever. And the same goes for the relays I repaired for local owners. It was always the solder joints.

DME Relay - Failure and Repair

Higher than expected current draws. An intermittent bad connection somewhere leading you to believe it is the relay. I'd check the relay and the socket it sits in and associated socket wiring first.

Do a search for the title (DME Relay Explained) There is a good write-up with picture of how to repair the relays. Deals with reflowing the solder joints..

For what it's worth, I had a situation where my car ('90-C4) would intermittently
start then not start after shutting it down.

Turns out that the problem was NOT the relay but oxidized contacts in the relay socket . The car had been left out in a deluge of a two day storm and apparently the relay compartment took on a bunch of water which led to the oxidation/corrosion problem.

One socket at a time, I took some 400-600 grit aluminum oxide emory (which I had previously laminated to some very thin sheet metal to form a very fine emory board.)
and cleaned the relay sockets. After that I sprayed all the contacts with electronic contact cleaner to further "flush" the socket contacts clean...followed that with a gentle blast of filtered compressed air. Started up right away and never failed again.

That was six years and 5,000 miles ago.;

Hope This Helps!

Tony :)