Fried just the DME relay or worse...?

[Icemaster]

I reached under the drivers seat a couple weeks ago to retrieve my coffee mug, doing so knocked the cover off the DME relay and snagged a couple of the wires off the relay itself. During the ensuing wriggling of my hand, there ensued a series of sparks, some smoke, and a few dollops of melted solder from the tops of the female barrell connectors.

Got everything wired back up and secured properly, pleanty of crank, no start. I figured I probably fried the relay and shortened the lifespan of some of the solder joints - a couple looked cracked but my eyes suck. While the relay was opened up I figured I'd mess around a little, so I wedged in a shim on the fuel pump relay, cranked, fired right up and ran like there was nothing wrong.

I replaced the relay, same damn thing. No click either on the new relay - dead air. I get 12 v across all terminals at the relay except 87 when "On".

So - WTF now? Did I fry my ECM?

I've started at the simple - fuses, connections, everything I think would be the obvious after affects of a short and I'm stumped.

Any suggestions?

[equality72521]

Oooh Pete, sounds like you may have damaged the ECM. If you swapped a known good DME and it still doesn't fire sounds like bad news. Have you looked at the ECM for burnt traces or components? Maybe you can get JEOII or one of his group to build you a new one

[Icemaster]

Yeah, I'm not real happy at the moment. This all happened the evening before P2O. I haven't pulled the ECM out and opened it up yet, I'm gonna try that before I go pulling the fresh air blower and bypassing the alarm module, although I'm leaning more towards that than the cooked ECM right now. I can get everything running perfectly if I manually close the fuel relay. Took a nice run yesterday with the plastic VOM probe cover wedged in there.

We've got a pretty nice lab, I wonder....nah....

I need beer.

[rick-l]

Here is what drives the fuel pump relay in the DME. ADV7 comes from the processor and the signal through R750 is the yellow starter wire.

Does the voltage on pin 20 go low when you crank it? How about when it is running?

EDIT: are you sure you are forcing the fuel pump relay closed or the DME POWER closed?




http://www.frwilk.com/944dme/

[Icemaster]

Thanks for making me go check...I was wrong. It is the DME power relay that I'm closing, not the fuel pump.

I'm pulling the ECM this eveing. What should I be checking? I still have my stock chip I could swap back in.

[rick-l]

Originally Posted by Icemaster

Thanks for making me go check...I was wrong. It is the DME power relay that I'm closing, not the fuel pump.

I'm pulling the ECM this eveing. What should I be checking? I still have my stock chip I could swap back in.

The power side of the DME relay is driven by the ignition switch in the on or start position. You should check that wiring.

There does not appear to be anything wrong with your DME.

[ischmitz]

I second Ricks comments. It might be as simple as a burned relay socket contact. Don't (yet) mess with the DME itself if it was the power stage of the relay that did not actuate. Remove the DME relay and check Terminal 86 (+12V from ignition switch through alarm module with ignition ON) and Terminal 85 (GND). That is what actuates the first stage of the relay.

With the ignition switch in ON position the power stage of the relay needs to close and the ICV in the engine bay is supposed to hum (DME CPU running).

Ingo

[Icemaster]

OK, so no power across either 85 or 86 with the ignition on. Only place I got power was from 30 - and if I'm reading the diagram right - that's direct to the battery. All the barrell connectors look sound, I'm checking the ignition switch now.

[dshepp806]

Originally Posted by ischmitz

I second Ricks comments. It might be as simple as a burned relay socket contact. Don't (yet) mess with the DME itself if it was the power stage of the relay that did not actuate. Remove the DME relay and check Terminal 86 (+12V from ignition switch through alarm module with ignition ON) and Terminal 85 (GND). That is what actuates the first stage of the relay.

With the ignition switch in ON position the power stage of the relay needs to close and the ICV in the engine bay is supposed to hum (DME CPU running).

Ingo

+1. Don't yet think it's the DME...

you mentioned "melted solder",..WTF? Where?

Best,

Doyle

[Icemaster]

The melted solder came off the top of the barrels that connect to the relay, it was a couple of tiny drops that are used to seal the wire to the connector. All the connectors are good.

[Wayne 962]

I agree with Ingo, check the sockets there and don't move, touch, or mess with the DME right now. The fact that the car ran well when you manually operated the relay means that the DME is probably fine...

-Wayne

[Icemaster]

Yeah, thats what I'm thinking also. This is starting to become extremly irritating, especially now that the trigger for the drivers side door just snapped off. And the window is now out of the track. And theres a nice new dent from a black walnut hitting the hood.

What freakin next.

I'm bypassing the alarm module and trying that. I can't find anything else.

[Wayne 962]

Originally Posted by Icemaster

Yeah, thats what I'm thinking also. This is starting to become extremly irritating, especially now that the trigger for the drivers side door just snapped off. And the window is now out of the track. And theres a nice new dent from a black walnut hitting the hood.

What freakin next.

I'm bypassing the alarm module and trying that. I can't find anything else.

My suggestion is to take a break for the rest of the day. I find that when I work on the car like this, I tend to do silly things that cause more damage...

-Wayne

[Icemaster]

I would, but I do my best thinking after dark.

It was the alarm module. The underseat fireworks from a couple weeks ago must have fried it. Bypassed now, fires and runs beautifully.

The fresh air blower being out for this fix, now I can reverse the wipers. The glass has been out of the track for a bit now, I had to open the door up anyway. And I can R&R the handles and get them looking and working nice. If craps gonna break, I'd rather it be all at once rather than a piece at a time. Silver lining is always there, just have to look for it.

Thanks for the advice and suggestions gentlemen.

[Wayne 962]

Cool, glad to hear it. I've never really known why those goofy wipers block everyone's views. I've heard many viewpoints on it - none of which seemed to make any sense. I did that on my SC, I think I might do it on the '72 RS clone too...

-Wayne

[richde]

Originally Posted by Wayne at Pelican Parts

Cool, glad to hear it. I've never really known why those goofy wipers block everyone's views. I've heard many viewpoints on it - none of which seemed to make any sense. I did that on my SC, I think I might do it on the '72 RS clone too...

-Wayne

Because when it's raining, the water streaks back up in front of the driver without the wiper there to hold it back/deflect it.

Much better when the sun is out, not so much when driving in the rain.

[scarceller]

Originally Posted by Icemaster

I would, but I do my best thinking after dark.

It was the alarm module. The underseat fireworks from a couple weeks ago must have fried it. Bypassed now, fires and runs beautifully.

The fresh air blower being out for this fix, now I can reverse the wipers. The glass has been out of the track for a bit now, I had to open the door up anyway. And I can R&R the handles and get them looking and working nice. If craps gonna break, I'd rather it be all at once rather than a piece at a time. Silver lining is always there, just have to look for it.

Thanks for the advice and suggestions gentlemen.

Nice find, the alarm module is what picks (activates) the DME relay. So did you simply remove the module and jumper 2 pins at the module harness?

[Icemaster]

There's a couple of good threads on the topic, the best instructions were here:

How do I disable alarm w/o key? 87 Carrera

[Wayne 962]

Originally Posted by richde

Because when it's raining, the water streaks back up in front of the driver without the wiper there to hold it back/deflect it.

Rain? What's that?



-Wayne

[Icemaster]

Drippy wet stuff that falls from the sky and causes gridlock, mass confusion, and media blitzs touting the "End of the World" when it occurs in SoCal.