Bob - 95 993/C2

After parking the day before yesterday, I hosed off the overnight dust and tried to start my 95/993. It cranked a while (usually starts right up)coughed and caught momemtarily then shut down. Still cranks great but no start.

Feels like no gas (got half a tank) or water at distributor but that has never happened before. I sprayed off the "outside" of the car...but did direct some water at the rear vents but no more than a normal wash.

Before I go tearing into in, anyone have any specific ideas?

Thanks!

E. J. - 993 Alumni

Bob,

The car is a 95, and you had problems after hosing off or washing. This is appearing to be one of the tell tale signs of wiring harness failure. Do a search for wiring harness if you are not up on the issue. Might also check out my web site.

E. J.

911-TOUR

Let the car sit overnight...if it still won't crank in the morning, have it towed to the nearest shop. Had you driven the car hard on a warm day immediately before rinsing the dust off ?? Could be vapor lock. I used to get vapor locked in CA on a hot day.

sean

tom97c4s

Sounds like it could be a dme relay.

Bob - 95 993/C2

Still did not crank the next day.

No water visible on the motor now or after I rinsed the car, really...I'm optimistic that the wiring harness is okay.

Ordered a DME relay from Suncoast yesterday (and a spare). Two for what my local dealer wanted for one!. I'm hoping that's the problem and will let you know. Thanks for the ideas!

Greg Fishman

[quote]Originally posted by tom97c4s:
<strong>Sounds like it could be a dme relay.</strong><hr></blockquote>

I agree. If you want to do a test use a jumper wire to connect the three positive connections and see if it starts. Only problem then is that the fuel pump won't turn off when you stop the car and have to unplug the wire.
If it is the DME relay, also known as the fuel pump relay the car will turn over but it won't catch.
Sounds like a good place to start. And per Steve W's recommendation I alway carry a spare.
Greg

Flying Finn

Sorry being stupid, but... Anyone has a picture where it is?

Bob - 95 993/C2

<a href="http://www.miataforum.com/bobh/993_dme_relay.htm" target="_blank">Pictures of the Relay</a>

Flying Finn

Thanks Bob!

I'll go & get one & carry it for the spare.

Bob - 95 993/C2

It was the relay! Thanks, Tom for reminding me and others for the advice.

Robin has added the pictures and process to his DIY section for future reference.

tom97c4s

I'm glad it worked for you. Lets hope all our fixes are this easy.

Robin 993DX

Bob,

I was thinking about your bad relay issue a little more today and I have made the following theory that I wanted to share.

As far as I know, mechanical coil relays don't fail that easily and quickly. The fuse box is located in the front of the car, and it is sealed pretty well, so there is no way water can enter the fuse box and cause the relay to burn out. Obviously there would have been more damage than just the relay.

So I asked myself this question, what caused that relay to go bad?

Maybe there is a short somewhere in the harness that caused the relay to burn out?

Maybe this is a sign of a bad harness?

What's the relation?

tom_993

Hi Robin,
Interesting theory. I guess you’re thinking along the lines of something shorting in the harness, and sending bad voltages to the relay. I suppose it could happen. Let’s see:

My harness failed, but my relay is still OK (possible point against theory).

I have a new harness, and my relay is still OK (possible point in favor of theory).

Here’s an interesting question. These relays have a 944 part number. Do they ever fail on 944’s? I did a search of the 944 part number (944.615.227.00) (nothing came up) and then the words “DME Relay” on the 944 board. I found a bunch of references, including suggestions to carry a spare, but in the few messages I looked at, no one actually said that theirs failed and replacing it solved the problem. If they never fail on 944’s I’d guess that there is nothing inherently wrong with the relay itself.

Sound logical?

Tom

Robin 993DX

Yes Tom, very logical thinking.

Here is another question I was also thinking about:

There are several more similiar relays in the fuse box, I don't believe I have ever heard of anyone complaining about their other relay failure other than the DME relay.

Now of course one would say, that the DME relay is used more, but what about the fule injection relay? It should have had the same usage frequency as the DME relay.

Regarding this theory:
My harness failed, but my relay is still OK (possible point against theory).

All of the bad harness wire that were replaced didn't have some sort of common wire that had bad insolations. It was sort of random, so maybe when your harness went bad it didn't effect the wires that lead to the DME relay?

I am glad to see someone else participate in this brainstorm.

Thanks

tom_993

[quote]All of the bad harness wire that were replaced didn't have some sort of common wire that had bad insolations. It was sort of random, so maybe when your harness went bad it didn't effect the wires that lead to the DME relay?
<hr></blockquote>

Yep, that's why I said "possible."