GentlmnGQ1

I Just had my turn at the failing DME relay experience. I thought I would share the details of said experience as well as describing the signs that my DME relay was failing.



About five years ago, I had a no start problem and purchased a DME Relay as a possible remedy. It turned out that my crank sensors had failed and my DME Relay was fine. Since DME relay failure is a common ailment among our cars, I put the new one in the glove box just-in-case. It was in my car for a long time but then ended up staying in my Autocross equipment bin as I got tired of removing it(among other things) from the car before each race.



For the past three months I have had intermittant no start problems where the engine would turn over but not fire. The first time, it only took a few tries to get the car to start and it didn't show any signs of trouble for another month. Gradually, the frequency of the no start problems increased and each time it would take more attempts to start the car. In the end, every time I went to start my car, it would take at least fifteen minutes worth of attempts to get it to fire. This would happen regardless of engine temp, how long the car would sit, or weather conditions. Also, just before the DME relay failed permanently, the car would randomly shut off when slowing to a stop on smooth road. This happened a week before as well as the same day as the permanent failure.



A few days ago, I drove the car to a meeting at work. When I left the meeting two hours later, the car started, stumbled, then stalled. I tried again with the same result. After that, the car would not start no matter how much I tried. Plenty of crank but no fire. I had someone crank the engine while I listened for a hum from the fuel pump. No sound. I figured the DME relay had finally quit on me. Unfortunately, since I had taken my spare DME relay out of my car some time ago, I couldn't test this possibility.



I got a ride to my house where I tracked down the spare DME relay. In case the relay wasn't the problem, I also gathered a spare ignition coil, my multimeter, a fuel pressure guage, a tool box, a jump pack, and a jumper wire to bypass the relay. When I went back to my car a day later, it still wouldn't start. I immediately replaced the DME relay and it started right up. I shut it off and, to be sure, I put the bad relay back in and (curiously) it started, stumbled, then stalled. Then it would not start again. I put the good relay back in and have had no problems since.



Needless to say, I will be ordering another DME relay soon and will be sure to keep this one in the car.

todzilla

Great write up! Just bought my 951 and I think having a spare would be a wise investment.......can you tell me roughly what they're worth? Is this under the passenger carpet in the footwell?

Cheers

GentlmnGQ1

Thanks! I hope it helps others diagnose their no start problems with similar symptoms.

The DME relay is in the fuse box under the hood on later cars. Bought mine new for around $20. You are thinking of the DME computer which is indeed under the carpet in the passenger side footwell. Not sure of rates on those.

catamount

Nice little write up, thanks.

I have wondered about my DME recently. I don't have starting problems but soon after starting from usually cold I'll get a stutter as I begin to drive. This usually settles down once the car is slightly warm though.

ekeeton

Note to self: buy spare DME relay NOW. Keep in glove box permanently.

Z-man

I always have a spare DME relay in my glovebox -- and I had to use the spare on my way to Lime Rock for a DE event last year.

BTW: if you don't have a spare, you can try to resurrect your DME relay by tapping it on the ground -- it sometimes shakes off the carbon build up on the contacts, allowing you to get back on the road. You should still carry a spare, but in a pinch, and in desperate times, this trick may work...

-Z-man.