DME Relay - Failure & Repair

[Traveller]

Background:
According to the date code on the relay casing, this is the original relay that came with the car when it was manufactured back in 1995.

The relay performed flawlessly in the time I've owned this 993 and failed shortly after removing the relay from the fuse & relay board. The relay was removed in order to pre-lube the engine after a long winter layaway. This enables the starter to crank the engine over thereby building up oil pressure while disabling the fuel injection circuit.

Removing the relay from its socket in the fuse & relay board was enough to cause a break in an existing faulty connection on the printed circuit board.

Having examined my sixteen year old relay (72,470 km - 45,040 mi), there really isn't any reason these should fail.

The two sets of contacts were in perfect condition as viewed under a microscope in my lab.

The single semiconductor, a rectifying diode on the board, is highly unlikely to fail. The same applies to the coils used as electro-magnets.

This leaves the solder joints; usually the cause of any electrical problems.

Solution:
The solder joints in the following photo were resoldered. The two solder joints within the yellow rectangle were the problem connections as the upper coil was intermittent when energized and only operated when pressing on the printed circuit board or side terminal (85b).




The following photos are for general information only...

The left side of the DME relay:


The front of the DME relay:


The right side of the DME relay:


The DME relay diagram on the case:


BTW, the Porsche part number on the top of the casing is 944.615.227.00. This relay is shorter in height than the spare DME relay (Porsche part number: 993.615.227.00) that I purchased back in Oct 2009 for $29.31.

[Joe Bob]

Early 964 engines will use the 3.2 style DME relay.

http://www.pelicanparts.com/cgi-bin/smart/imgdsply.cgi?pn=91161815400-M252

Porsche 911 & Carrera Gauges and Miscellaneous - Page 4

[Traveller]

Originally Posted by Joe Bob

Early 964 engines will use the 3.2 style DME relay.

And just as repairable in 5 minutes. I would assume the cover pops off as well?

[Joe Bob]

Yep, I bought a spare when I thought the orig went bad. It ended up being a short in the switched power for the DME. I have a 91 engine....

[redturbo911]

Great insight very helpfull and interesting to know.

[Traveller]

Not all of them fail alike.

I got this relay from a fellow 993er to have a look at and repair.

Quite obvious is the connection with no solder and the darkened circuit board due to heat.

The contacts across pins 30-87 gave variable resistance readings of 50 to 200 mΩ when switched; they should be less than 10 mΩ. Those contacts were cleaned up (now reading 2.2 mΩ) and the contact that could be adjusted, was.

[lupin..the..3rd]

Originally Posted by Traveller

Background:
The relay was removed in order to pre-lube the engine after a long winter layaway. This enables the starter to crank the engine over thereby building up oil pressure while disabling the fuel injection circuit.

When I pull my car out of storage, I find it easier to pull the fuel pump fuse instead. It accomplishes the same thing and is bit easier.

[Lorenfb]

"Early 964 engines will use the 3.2 style DME relay."

Wrong, guess again, round pins vs flat! Continue to post to the simple ones,
as always, in an attempt to just raise your "count".

[miky]

good day all and tks for give me opportunity to enter here
well I am on italy and have a 911/964 made 1993 .
the problem is that my car run but I DO NOT UNDERSTAND WHY ? sometime the light of 4wd and ABS switch on , on my pannel control.
So now I ask you if the DME relay control the fuel pump , the engine , and also other parts?like bebore descript.
On other way ..........what is the function of DME relay and what is the parts that control?
tkn and regards
miky

[porterdog]

Originally Posted by miky

sometime the light of 4wd and ABS switch on , on my pannel control.

This is often related to the brake fluid level. It must be at max, with the car running.

[RW964]

Just my $0.02 I would and have purchased a extra dme relay seems like the $25.00 American or close to it that you will pay is worth the time and money to have some insurance in the glove box. I also have the jumper wires for a backup to the backup. All I need to do now is fuse the jumpers for a just in case you never know what is going to happen.. Better than sitting on the side of the road esp. at night ...........

[964TargaC2]

A word of thanks to the OP, with the info he provided I was able to fix a brand new relay that did not work....

Folks..Dont assume that the New relay you bought will work, After reading this I went and checked my spare and it did not work and it was OEM not some aftermarket piece!

[Don Plumley]

As a general rule of thumb, with my last two 911's, the first thing I did was buy a new DME relay, put in the car, and pull the old, working unit out and save it as the spare.

That way I'm a) less likely to ever have a DME relay fail (there's a new one in use); and b) if I do need a the spare, I know it worked when I pulled it out.

[964TargaC2]

Mine was a simple fix..just a bad solder at one of the terminals but I would never have gone in there had I not read this post

[Traveller]

Originally Posted by 964TargaC2

Folks..Don't assume that the New relay you bought will work. After reading this I went and checked my spare and it did not work and it was OEM not some aftermarket piece!

Good point!

I once installed a new set of Bosch points and condensor in my mom's real Beetle when I was a teenager. The car wouldn't start. I was checking everything else and in the end is was the NEW set of points.

I'll pop the cover and check my new DME relay. Its an original Porsche unit as well.

I just pulled the cover off the blower fan relay that is found in the driver's side electrical panel in the engine compartment. All solder joints looked OK until I put the relay board under a microscope at work. Sure enough, there were fissures in some of the solder joints. It hadn't failed yet, but I un-soldered all joints, cleaned them and then re-soldered them all...all joints are smooth and shiny now.

[Traveller]

Originally Posted by Don Plumley

I know it worked when I pulled it out.

So did my original DME relay...till I pulled it out. It was that action that caused it to fail.

[roadsterswap]

When the DME relay is not working, what do you see with the car? will it not start? no fuel pump noise? what?
i have a 77 with a 85 3.2 motor in place. i went for a drive. all things working well. I cam home for 1/2 hour, went to start the car and the starter would not turn over at all.
fuel pump on. Key goes through the right motions.. I read that the DME may be a problem. I took the cover off and watched it switch each time. I had decided to push start the car and it fired right up and i drove back to my shop. Starter will not spin. no noise. nothing.
I would think it is not the ignition switch. power is getting to the dme relay. Nothing to starter? I checked the fuses under the hood. looked at the wires under the car to the starter. No oblivious issues.
I was going to get the DME. if anything for a spare.
Get an ignition switch plug, if any reason but to have a spare??

pull the starter? Any thoughts? tim

[964TargaC2]

Check the lead to the solenoid, I just went through the trials of starter replacement, put the new one in and nothing...turns out one of the problems was the lead from ignition switch to solenoid (starter was on its way out as well)

quick way to check it is bridge the hot lead at the starter to the solenoid, if starter engages then its likely that lead from switch to solenoid..

[roadsterswap]

I will check that first thing in the morning. Thanks.

[posers]

where is it located on a '93 C2 RSA? I was told under the drivers seat, but can not seem to find it there...