Electrical Fire!

[dtool242]

I might be a little over-dramatic with the title as it didn't devolve into a full-blown fire. But there was a good deal of smoke and a wire glowing red.

So here are the details so far. Drove my 86 to the local cruise night, when I went to leave the car would turn over but wouldn't start. After a few attempts at starting the car I noticed a little stream of smoke coming from the passenger foot well. Pulled back the carpet and opened the cover to release a large cloud of smoke and saw a wire coming from the 'W' connector (the one on the far right) glowing red. At this point the ignition was off with the key out so I ran to the back and disconnected the battery as quick as I could.

About this time it starts raining so I just call a tow truck and have it towed to where I work. We build equipment for nuclear power plants so we have lots of tools there and since my boss is a car nut, we also have a lift in the shop.

I haven't really dug into it yet to see what the problem is. I intend to get at it after work this evening. Early suspicion is something related to the fuel pump got shorted out? Anyway, not necessarily looking for advice or help yet as I haven't provided enough detail for anyone to do so. Just a heads up that it will probably be coming I intend on updating the progress on this as I go.

Anyone else experience something like this?

TIA
Alan

[dtool242]

Oh and I should mention I don't have any electrical diagrams for my car. I suppose that is the first thing before I start this. Anyone know of a link to one online somewhere? I haven't run across on yet.

[Alan in AZ]

Most of the W's go directly to the LH ECU (Air/Fuel ECU) - which wire connector was it: bottom left is W11 top left is W15, bottom right is W21 top right is W25...?

Yes you will be needing the factory diagrams the online sources seem to have dried up - you can order via Roger at 928srus.

Alan

[dtool242]

The wire coming from W12 has about a 2" section of insulation burned away. There are 3 wires coming from W13, two of them are red with a yellow stripe and are intact, the third has the insulation completely burned off and has broken as well. Looking at the bundle coming from there, the sleeve is scorched/melted all the way to the penetration in the fire wall. Looks like I'll be replacing that wire bundle along with figuring out/fixing the root cause of this.

Thanks Alan!

Alan

[Alan in AZ]

W13 has 2 thick wires (red/yellow) and 1 thin wire (Blue) the thin wire goes to the Oxy sensor in the exhaust, the other 2 feed the power side of the fuel injectors (they are switched on the ground side) - these are all fed by the XX Fuel Pump relay (there is no fuse in these lines - though there is to the fuel pump).

W12 (brown/red) is fed by the LH injector pulse signal (brown/red wires from LH pin 13 - so check that) it also connects internally within CE to J12 (yellow) that feeds the pod fuel consumption guage.

I think what is most likely is that a connection on W13 caused the problem due to a short somewhere in the engine compartment - Could also possibly have been the Oxy sensor wire shorting on the exhaust - but I'd expect that thinner wire to have simply melted though...

Some of the damaged wires may have just been collateral impacts... try to identify a single cause

You should get a new XX relay - it wasn't the cause but it likely has very damaged contacts by now...

Alan

[dtool242]

The two thicker wires on W13 were the undamaged ones, the thinner one burned through. I have a new fuel pump relay in hand. Don't have a fuel consumption gauge on my car.

Just noticed there is another wire bundle that comes through the firewall that has a thick green wire that goes to a connection not on the CE and thinner blue and brown wires that go to a connector (again not on the CE) that has white wires coming out the other side of it. I believe these two white wires go to the O2 sensor before the cats... correct? Anyway, this bundle has some pretty severe melting right at the firewall penetration and for about 3" into the passenger compartment. Doesn't look like it's collateral from the other bundle as the melting looks more severe on the smaller bundle.

I'll take some pictures and get it up on the lift to check out the O2 sensor and also where the bundles come through the firewall into the engine compartment.

Thanks for all your help so far. You are a valuable asset to this forum!

[Alan in AZ]

Green (with grounded shield), Blue & Brown are the oxy sensor wires. Check the exhaust for a shorted spot due to contact.

Alan

[dtool242]

So I'm about 99% sure the problem was the O2 sensor shorting/grounding out. And 100% sure it is all my fault. It is about the only electrical thing I have messed with on the car, other than replacing the dash light dimmer.

Last year I replaced the transmission. To do so you have to remove the exhaust. Easier than breaking it at the clamps aft of the cats is to just unbolt it from the headers and drop the whole thing. But to do that you have to a) remove the O2 sensor -or- b) clip the wires and splice them back when you replace the exhaust. I went with b).

I used crimp-on butt connectors and also didn't even tape over them with electrical tape. So when I got the car up on the lift I found that the plastic covers on the connectors on the white wires had dried/shrunk/slid off the metal part of the connectors. Undoubtedly making some sparky sparks on the exhaust.

Here's the pictures I took. First is the damage in the footwell. The bundle you can see with the extensive melting/scorching is the one going to (coming from?) the W connector. Also you can see the bundle running down in front of the CE that goes to the O2 sensor. Hard to see the extent of the damage to it in this shot.



The next shot is in the engine compartment below the air cleaner box. The badly damaged wires are connected to the ground underneath the bundle.



The big main wire bundle going through the firewall has spots along it where the cover is melted. I guess it is probably safe to say I will need to replace the whole wiring harness to the engine.

[dtool242]

While google searching for a replacement wiring harness, I ran across this PORSCHE 928 FACTORY SERVICE MANUALS AND WIRING DIAGRAMS good resource for wiring diagrams.

[Danglerb]

Originally Posted by dtool242

While google searching for a replacement wiring harness, I ran across this PORSCHE 928 FACTORY SERVICE MANUALS AND WIRING DIAGRAMS good resource for wiring diagrams.

Those links look like they are to copies of the CD set Jim Morehouse made, most of us feel his work is worth paying for.

What I like it to take the files from the CD and have the diagrams for my model years printed on a large format printer, easier on the eyes, and you can mark up changes and highlight specific circuits.

[dtool242]

Finally got it out of the car. Looks like it's going to take more work to repair than what I want to do. Made some calls, looks like my options are a used one from 928Intl for $400 or a new one from Germany for ~$2500.

[19psi]

How extensive is the damage? Did it get into the sealed portion of connectors?
If not, I'd break out the soldering gun, spare wire and heat shrink tubing.

[dtool242]

It is repairable, but will take more than $400 worth of my time.

[Danglerb]

928Intl will send you out a good harness with a one year warranty within hours of you calling, but if you are on a budget and can wait look around and maybe something cheaper will show up.

Last one of those harnesses I recall someone buying from the dealer was more like $1300, six months ago one (new) showed up on ebay and took months to sell at $500 or so.

[dtool242]

And she's back on the road!

Big thanks to Alan in AZ for all his knowledge in 928 electrics, and Landseer for the replacement harness.

Drove out to his place in Indiana (about 2 hours from me) on Saturday to pull the harness off his 86.5 parts car, and picked up a few other goodies. I'm not going to say this guy is a 928 hoarder, but.... if people in the upper-Midwest area need some parts, check with him. He has tons of stuff and is a great guy!

[Landseer]

Glad to hear its running again.

Remarkable turnaround on this.

The car suffered a major short to the core wiring harness last week.

Its already fixed. Nice work.