Fried DME relay.. twice
 

Hello there- this is my first post here and I'm sure many will follow. Im the recently new owner of an 84 Carrera and I am very happy about it.
I have searched the boards and found numerous similar afflictions, but I have been able to locate the problem, or the result of the problem.
Under strong acceleration ( its happened 2 times only)the car just sputters, looses power and craps out. It turns over fine but will nor restart. it almost caught a few times and sputteres rough at idle but no power at all if i try to accelerate. Died after 10 seconds.
First stall I towed it to mechanic who determined it was Cylinder head temp sensor which he replaced as well as the flywheel sensor and speed sensor on the left side of the engine. It ran well for about a week.
second time- strong acceleration to pass a dumptruck, I smell a strong sour electrical smell and the car sputters and dies. The engine turns over, all electrical & gauges seem fine but will not start. A new friend and porsche owner pulls over and offers me a new DME relay. I pop it in and the car starts first try and runs smooth for about 10 seconds and dies. We tow it home, and today I took out the seat to look around and took apart both the original and the new DME relay and they are both fried in the same spot. It appears to be melting at # 87, on the top left corner.
Can anyone suggest what this may be a symptom of? I have no books/bently etc yet but working on this over the weekend.
Any help is greatly appreciated.
Thanks
Scotthttp://forums.pelicanparts.com/uploa...1337461291.jpg

Scott

Welcome to the club.

The only help I can offer, is... well, a pic of you car will probably start a deluge of potential solution :)

87 feeds power to DME and possibly coil if not mistaken. 87b feeds fuel pump.

Here you go JJ 911-
Yes it is in need of a tune up, but...

http://forums.pelicanparts.com/uploa...1337467016.jpg

Just joking

Seriously- I pulled back the plastic hose that surrounds all the wires leading into the DME receptacle and 4 wires were spliced(home job wrapped in cloth tape) into one which leads to the faulty # 87 terminal. One red, 2 red/yellow, one blue/yellow. Is that right?

You should get yourself a Bentley manual for your car ... those books are a must unless you like taking your car to the shop every time something goes wrong !

I'm sure somebody with extensive electrical knowledge will chime in and help you :)

Welcome and Cheers !
Phil

DME Wiring Color Code.
 

DME PIN # SIZE (mm) color & function

87B .75 GE Pin #2-O2 Sensor & 2.75 RT/GN-Fuse

85b 1.0 SW/WS-DME

87 6.0 RT-12V

85 1.0 BR-Ground

86 1.0 SW-burglar Alarm

30 4.0 RT-12V From battery

http://forums.pelicanparts.com/uploa...1337477780.jpg

If needed, I can send you a copy from my factory manual.

Good luck,

Gerry

Thank you Gerry- Would you think that means only one wire(6 mm red) is supposed to be leading into terminal 87? I would, but at the terminal there are 4 wires spliced into that #87 pin that connects to the DME relay. could be overloading it.

Can you trace where the splices go? I assume they're not factory....correct?

Dme
 

It would appear that someone has been playing "Fingerpoken".

What color wires are on the splice?

The 6mm red wire feeds the other functions when the ignition key is "on"
such as the IDC, the DME ect...

Here is the CKT diagram.

pm me as needed.

Gerry

http://forums.pelicanparts.com/uploa...1337493252.jpg

My SWAG, but sounds like bad VR (voltage regulator) to me . . .


IMHO, Bentley + 101 projects are must-have, first purchases. My best advice is don't go poking around or DIY -- especially w/engine management systems -- without good tech references. This ain't a Kia.

Thanks Gerry for the diagram, It appears that splice is a factory splice according to the diagram. What book did you get that from?

Flat Six- I am thinking that could be the root of the problem as well, a bad voltage regulator.
Anybody else ever seen this or know what could cause the DME relay to cook like this?
I have some time this week and am going to try and get it all figured out.

wehrle (sp?) or uro brand?

John Walkers- Hi! I remember your shop- I lived in Seattle and drove by often, before I had a Porsche. Are you asking who made the Voltage Regulator or DME relay. I havent gotten in there to inspect the VR yet- Looking if there is a way to test it with it in place. Battery with engine off is reading at 12.6 volts.
Thanks

Looks like damage at the top pin in the picture as well.

i can't see the voltage regulator being the problem. lots of them go crazy and charge 17V and this doesn't happen. something in the circuit obviously went to ground or is drawing a huge amount of amps.

Sure no one has tapped 12v switched power from the 87 wire? It is red and about 8 gauge in size.

To me, either something has shorted inside the DME or related sensors or someone tied a huge load on pin 87 wire.

A real easy check is to (disconnect battery first!) disconnect plug connecting to relay. Pop off cover and make sure none of the wires are grounding to each other. It may not cause this condition but it's easy to inspect.

Just a thought.

With the engine running you should read at the battery around 13.8 volts which would mean the VR is ok.

If it read 17 volts or more, is a goner but like JW said would not do anything to the relay, the car will still run but it will boiled you battery and may damage some electrical component, BTDT :(

Thanks guys for the thoughts on Voltage regulator. Because the car wont start because of this problem, I cant test the battery with running voltage. 12.6 with engine off. Maybe something could have shorted or grounded when the cylinder head temp sensor and the other 2 sensors were recently replaced in the shop. The mechanic is on vacation till the 29th so I am sleuthing this out on my own with all your help.
Thanks
Scott

Dme relay
 

Here are a few more hints.

As per the previous poster, I doubt that there are any issues with your VR.

I would be looking for an additional load on that circuit.

Do you have any blown fuses?

Start by liftng the connection to the o2 sensor.

http://forums.pelicanparts.com/uploa...1337628022.jpg

Hey thanks for that last bit of information. I am not at the car right now, but I do know the O2 sensor is not connected. I noticed it loose in there dangling on the left side when the 3 sensors were replaced. The mechanic said it wasnt necessary, & the car would probably run leaner with it but he didnt replace it. Maybe it moved and hit something causing a short. Ill check that when I get home.
Thanks so much.