DME Relay - carry the spare.

[howard freeman]

The originals fail due to melted solder joints. Resolder the joints & throw it in the glove box as a spare. Uro parts stink,use only O.E. & I have had good luck with K.A.E. in the past.
Howard

[chococrazy]

Rather than carrying a spare a lone, carry a spare with a paper clip on it to use as a jumper. That way if you REALLY need it you know it won't fail..

[Arne2]

OK. First, the disclaimer. This jumper should NOT be used as a normal replacement for a DME relay. It should be considered as an emergency bypass to get you home in event of a DME relay failure on the road. Be warned that with this bypass in place, the fuel pump will run whenever the ignition switch is in the Run position. (This differs from the actual relay which only energizes the pump while the starter is cranking or the engine is running.)

That said, the jumper is simple. I will not provide a diagram, as looking at the picture below should be enough. The male bullet terminals are the common .157" size, and you should use a relatively heavy gauge wire. Mine is 12 or perhaps 14 gauge. (I can't recall for certain now.)

To use the bypass, you'll need to unplug the harness from the failed DME relay, and then plug the jumper wires into the terminals that would normally connect to the relay terminals marked 30, 87 and 87b. (I put a dab of white-out on the connector to mark the three proper terminals so I wouldn't have to figure it all out again while stranded on the side of the road. See picture below.)

If the DME relay has failed, but everything else is OK, this will get you home. And it shouldn't go bad from the vibration of rattling around in the glovebox for a couple of years, either.

If/when my next relay fails, I may build a replacement instead of buying yet another fragile dual relay. Looking at the schematic and such, I could build a simple replacement to duplicate all the factory functions using a pair of standard 20 amp lighting relays. Parts for that would be available at any FLAPS. That's a future project.

[Arne2]

Had to replace the picture of the plug, had it marked wrong. The plug terminals are marked 1-6. You want to jump 1, 2 and 6.

[SilberUrS6]

Arne, that's a good work-around. I like the idea of a robust dual-relay replacement, too. OK, so here's a dumb question. Let's say I want to do a 3-wire splice but NOT use a vampire tap - is there a crimp-type 1-in-2-out electrical connector for 16-12 gauge wire? Waterproof would be acceptable, but not necessary. Vampire taps usually fail, even when not in use, due to their design. I found this out the hard way. Twice.

[Arne2]

Several ways to do it w/o the vampire tap, but when I needed it to move my car, that's what I had on the shelf. But for example:

[SilberUrS6]

Originally Posted by Arne2

Several ways to do it w/o the vampire tap, but when I needed it to move my car, that's what I had on the shelf. But for example:

Yeah, that's about right. Where does one get such a beast? My local Radio Shack folks look at me like I have two heads when I talk about this issue (I've run into this before.)

My solution in the past has been splicing and soldering, which is great if the wires are where you can get at them easily...

[Arne2]

I can get those at my FLAPS, but maybe not at the chains like AZ or O'R. If that doesn't work for you locally, try someplace like Pico Electrical Wiring Connectors

[Canada Kev]

Seeing that it's just three wires all connected together at one end, you could use a Marette or wire nut on one end and the bullet connectors on the other. Hell, even if you're in the middle of nowhere with nothing, the closest farmer will probably have everything you need to make something like this and get you mobile again. Not quite as elegant as the stuff above, but it'e just to get you home, right?

[86 911 Targa]

Originally Posted by Arne2

Had to replace the picture of the plug, had it marked wrong. The plug terminals are marked 1-6. You want to jump 1, 2 and 6.

Well done Arne2, well done.....

Thanks,

Gerry

[ant7]

Hi All,
The coils in the DME can also go open circuit, mine had this failier when i got the car, to get round it someone had fitted a jumper wire in the fuse box.
Anthony.

[tazzieman]

Originally Posted by 304065

I used to carry a spare DME relay. The spare was the known good one out of the car. The replacement was the one I installed. That accomplished two things:

1) Put a known good DME relay in the glove box; and
2) Familiarized me with how to change the DME relay so the first time I did it at the side of the road with trucks roaring by at 80 mph in a rainstorm while kneeling on roadkill, it didn't take very long.

My thoughts exactly! On my DMEd car (the 944) I found the relay was hard enough to get to on a nice sunny day , with no traffic thundering past & under no spousal pressure - figured it was best to put in a brand new one and keep the perfectly functioning old one in the glovebox. No reason for it to deteriorate if kept in a sealed bag.

[Caferacer]

Originally Posted by 86 911 Targa

Hope this helps.

Good luck,

Gerry

Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

Thanks Gerry! Looks like the one in my Project List was indeed the URO.

[dshepp806]

I also installed a small pad under it to attempt a degree vibration reduction that it "feels".

I've mostly seen the contact failures (any of them), especially the fuel pump contacts. I've often wondered about an aging DME relay causing strange happenings, other than an outright failure. Although I've never tested this scenario, I often wondered about voltage drops occuring across the contacts (as it slowly becomes resistive) , resulting in less voltage to the fuel pump,..then what? Again, just curious about this impact on the fuel pump (proper) operation...Guess I'd have to look at the fuel pump specs to truly assess the "what-ifs"..

The other failure I've found (on a friend's relay) was solder fracture on the coil connection at the PC board,..resolder fixed that.

Again, I changed them out cyclically (preventatively)...never been a fan of any resistance in any contacts on any relays!!!!!!!!!!!!!!

BEST!

Doyle

[88911coupe]

Trying to localize a random no start situation and would like to try this bypass option. Basically what will happen is the car will turn over fine but never start. I just put a new DME relay in from our host and thought the problem was solved since I found a chunk of solder missing from he old DME. However after about 3-4 perfect starts the problem re occurred. I grabbed the DME, gently shook it a bit and could clearly feel the click at "on" position and then the car started fine and did so for several subsequent tries. So now I'm thinking maybe the new DME is buggy but it could be the rpm/flywheel sensors as well...very frustating! Anyway, I want to take the DME out of the picture by using the bypass...any danger in this, other than the fact that the fuel pump will run in the "on" position? I'm thinking if the problem does not occur for several days then it was the new DME being buggy...correct? There is another thread by Loren on how to test a DME relay but my ignorance on electrical issues leaves me with some questions on exactly how thats done.

[rick-l]

Next time it does not start why not stick a spare plug in a wire and see if there is a spark? That will take the DME mostly out of the picture.

[cabmandone]

I bought two new ones from PP when I installed my engine and had starting troubles with the one that came with my donor car. Once I got the car running I switched in the other new one to be sure both worked then kept the other in my glove box for emergency purposes. I don't know that it's a guarantee the other will work if/when I need it but i'd think if it worked out of the box it should work again.

[rick-l]

Also look at the tach when it is cranking.

The DME is separate from the DME relay. The DME relay is really two relays. When you turn the key to run the DME relay powers the DME and the injectors etc. When you turn the key to start the DME powers the coil in the DME relay to run the fuel pump.

[cabmandone]

Originally Posted by 88911coupe

Trying to localize a random no start situation and would like to try this bypass option. Basically what will happen is the car will turn over fine but never start. I just put a new DME relay in from our host and thought the problem was solved since I found a chunk of solder missing from he old DME. However after about 3-4 perfect starts the problem re occurred. I grabbed the DME, gently shook it a bit and could clearly feel the click at "on" position and then the car started fine and did so for several subsequent tries. So now I'm thinking maybe the new DME is buggy but it could be the rpm/flywheel sensors as well...very frustating! Anyway, I want to take the DME out of the picture by using the bypass...any danger in this, other than the fact that the fuel pump will run in the "on" position? I'm thinking if the problem does not occur for several days then it was the new DME being buggy...correct? There is another thread by Loren on how to test a DME relay but my ignorance on electrical issues leaves me with some questions on exactly how thats done.

I bench tested my old one by applying 12 volts to the coil of the relay. IIRC it's marked on the relay which two pins are the coil. Once you apply power to the coil the contacts should switch. I think one is normally closed and the other normally open. If they switch the relay "should" be good but my old one checked out okay and still didn't work. Somehow it was closing but not carrying power.

I'd check your connections for your speed and reference sensors in the engine compartment. I had one that was cracked on the sensor side and would allow the harness connector to slip off slightly causing a intermittent problem.

[88911coupe]

Thanks Cabmando, I'll check the sensors. They are relatively new since I replaced them when I rebuilt the engine a couple of years ago. Should it be "safe" to drive around with the bypass installed for a few days, just to take the DME relay out of the system and eliminate it as a possible cause?