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I fully appreciate the location of the burn through. There is nothing in the wheel well that could have caused that so obviously it went from inside the engine bay to the outside.
When I looked at your photo initially I saw what I was expecting to see in the form of two cables exiting the hot post. When looking at the pics again yesterday I realised that the photo suggested two cables taking the original routing and one cable in the foreground of the photo. I checked the 89 wiring diagrams and sure enough it seems they were equipped with three 4mm2 cables from the hot post to the central electrics, the cable in the foreground being the third such cable. My query was whether that third cable, when fed along the original cable route, would extend to the point of burn through. My assumption is that it will and that this cable will be the one that failed.
The other thing that struck me when looking at your original pics was how well the engine and supercharger location survived. The foam fuel rail cover is intact and yet over the wheel well, the aluminium fender has completely gone and yet there is not that much to burn under it- just the wheel liner. Even the front tire has survived for the most part or so it seems. How this fire did not take the rest of the car yet alone the entirety of the property is quite surprising really but of course a blessing for your business.. The aluminium melts at around 600C so that alone says something about the intensity of the conflagration. .
Yes, the plastic cover over the fuel rails was warped, but the fire self-extinguished just short of breaching the fuel lines. The RF tire was flat, having burned through on top. They said that the heavy smoke from the burning urethane, tire, and nylon; sealed in a room, is what extinguished the blaze. It literally snuffed itself out. I am so glad all my doors were new and weatherstripping was good.
My new Klein multitool arrived (Thanks Bulvot for helping me find the right tool for this) and we shoveled off the snow on my '91 and hooked it up right away. Dead battery! Ha! Its always something. I pulled the battery and brought it indoors, we are charging it now. Results on Monday.
I just took this picture from a 1995 GTS that is on our shop now for a engine rebuild. The spot I am pointing to is the location where our fire started on that 1989 S4 - behind this wire bundle is where it shorted to the inner steel fender. Granted, there are plenty of points along the unfused wiring that could fail - this is just where ours did. Anyway - thought you might find it helpful or interesting,
Where our fire started,. picture taken is a 1995 GTS
Pic from the 1989 S4 that burned.
My 1989 S4 (12/88 build) wiring looks just like the GTS wiring in your picture. The red conductors from the jump post to CE join the KS-1 harness on the engine side of the fenderwall, then pass towards the rear in that harness following the fender arch and over the shock tower, next to the coolant reservoir. They don't pass through the fenderwall into the wheel-well the way your failure picture suggests. Are you sure you were looking at factory primary wiring on the fire car?
My 1989 S4 (12/88 build) wiring looks just like the GTS wiring in your picture. The red conductors from the jump post to CE join the KS-1 harness on the engine side of the fenderwall, then pass towards the rear in that harness following the fender arch and over the shock tower, next to the coolant reservoir. They don't pass through the fenderwall into the wheel-well the way your failure picture suggests. Are you sure you were looking at factory primary wiring on the fire car?
I concur with Bob. My 89 is wired the same. Besides my wiring looks good, even after living in the Las Vegas heat for years, and Phoenix before being brought here. I'd venture to say the summers in the South West, are probably harder on the wiring than other locations in the country.
My 1989 S4 (12/88 build) wiring looks just like the GTS wiring in your picture. The red conductors from the jump post to CE join the KS-1 harness on the engine side of the fenderwall, then pass towards the rear in that harness following the fender arch and over the shock tower, next to the coolant reservoir. They don't pass through the fenderwall into the wheel-well the way your failure picture suggests. Are you sure you were looking at factory primary wiring on the fire car?
Bob,
What you are perceiving is an optical illusion. Because all the insulation and sleeving has gone what you see misleads the eye into believing that the cable is going through the wall in some kind of grommet. In fact the "mystical grommet" is the lower of two bolts that can be seen on the other shot taken outboard and the cable detritus or what little is left of it, runs behind Carl's wooden pointer back along the wall as per every other 928 but of course it looks somewhat diferent due to the fire damage.
Thanks Fred. From Carl's pictures, it looks like the wires pass through there where he points to the burned-through hole. Looking at a picture I have of mine and the picture of the GTS wiring (same...) it's hard to see how the primary wiring migrated from the engine side of the bundle out to the fenderwall side for the burn-through. There's a lot of bundle between the primary wiring and the fenderwall by my estimation, as the primary wiring has a pretty obvious loop that joins the rest on the side away from the fenderwall.
Further, it looks like the rest of that harness was destroyed/vaporized, as all but the primary conductors in the KS-1 harness are completely missing. Was the subject vehicle a road car, or had the rest of that harness been removed for track use? Carl?
Thanks Fred. From Carl's pictures, it looks like the wires pass through there where he points to the burned-through hole. Looking at a picture I have of mine and the picture of the GTS wiring (same...) it's hard to see how the primary wiring migrated from the engine side of the bundle out to the fenderwall side for the burn-through. There's a lot of bundle between the primary wiring and the fenderwall by my estimation, as the primary wiring has a pretty obvious loop that joins the rest on the side away from the fenderwall.
Bob,
On my GTS the two 10mm2 cables from the hot post loop through 180 degrees and into the main cable run such that they enter the run close to the fenderwall. The other wires in that run constitute those emanating from the 14 pin connector, and all the wiring that goes to the front of the car that includes the lighting, ignition circuits, ABS and other minor cables. The point being that when the car is not running the only live cables [electrical faults excluded] are those exiting the hot post. For sure the cable run is such that those live cables run close to where the steel structural wall has been breached. Not difficult to understand why the cable insulation failed but how it got past the outer sheathing as well takes some fathoming out unless someone has been dicking around with it [most unlikely I would think]..
There is also an earthing point with several cables close by. The ghist of what Carl intimated from the original investigation suggests that those involved concluded that there was a leak to earth from the live cable feeding the central electrical bus. On a vehicle that is shutdown the only credible explanation for the leakage is pretty much as assumed. The only other possibility I could think of is whether there was leakage to earth from the live cable via another degraded cable in the harness should there be one that is earthed when the vehicle is shutdown and thus started a fire that took out insulation and then all hell was let loose but to me that sounds awfully like double jeopardy- possible but not probable.
For sure nothing burning in that area could have burnt a small hole in a steel wall like that- there is nothing there that can burn that hot unless by some fluke a thermite process type reaction was triggered locally but I just cannot see that happening. On the other hand the battery in the 928 probably has a CCA of somewhere in the region of 700 amps. A bit of research suggests that a shorted battery of this kind could possibly sustain 1200 amps for a short while. The 30mm2 cable from the battery to the starter motor puts up little resistance and drops 1.4 volts, the 16mm2 from the starter motor to the hot post via the alternator will drop about 6 volts and the 4mm2 cable from the hot post to the fender wall location will drop about 3 volts. At 1200 amps the power being transmitted would be 14.4 kW! If all that power could flow through the 4mm2 cable that battery would last less than 4 minutes. A 4mm2 cable shorting the battery to earth will probably glow white hot and burst into flames immediately, the other two 4mm2 cables would catch fire almost as quickly and once the insulation breaks down would help sustain current flow. If the power is shorted and there is no filler rod it is not difficult to see how it will quickly burn a hole through the steel as it melts locally. To help visualise what we are talking about see the attached video clip
Here's a picture of the engine bay / light harness focusing on the area of the jump post. This harness connects to everything bolted to the engine bay sides and front except ABS/RDK/BPW. It's from a '90 but this harness is substantially the same 87+.
My 1989 S4 (12/88 build) wiring looks just like the GTS wiring in your picture. The red conductors from the jump post to CE join the KS-1 harness on the engine side of the fenderwall, then pass towards the rear in that harness following the fender arch and over the shock tower, next to the coolant reservoir. They don't pass through the fenderwall into the wheel-well the way your failure picture suggests. Are you sure you were looking at factory primary wiring on the fire car?
No sir, the car that burned did not have any wires that passed thru the fender well either. That after-fire pic shows where the wires ended up after the fire. That wire was pointing almost directly at the hole it had arced and created. The wire burned thru/melted and then broke the arc, much like Bulvot and others have said. It must have been damn hot, because it even lost it ability to support itself against gravity and dropped down from where it started.
Further, it looks like the rest of that harness was destroyed/vaporized, as all but the primary conductors in the KS-1 harness are completely missing. Was the subject vehicle a road car, or had the rest of that harness been removed for track use? Carl?
The harness in question - unless modified - does pass a branch into both front fenders. This harness connects to all of the lights in the front of the car. The pass-through is very close to the driving arm for the head lights.
As promised, I got outside to test my 928 that's been sitting in the snow outside for a while.
1991 928 GT
Parked outside, 20 deg F during this test, engine has 15W-40 motor oil in it, has not been started for 3 weeks
Not supercharged. No power-adders installed.
Peak Cranking Amp Draw: 1st test 279.2 AMPS; 2nd test 287.8 AMPS; and 3rd test 311.2 AMPS. As expected, as the starter warms up, it takes a higher AMP draw.
Note MEGA fuse in this car is a 300A Slo-Blow fuse. You can see it in the picture.
First crank test Second crank test Third crank test
Fluke is much nicer, but also much more expensive. So, I didn't recommend them since they probably aren't what you're looking for.
The Klein is more than adequate for this and has many other uses to boot. Just set it to measure DC amps and to hold the min/max values. Put it around the main wire from the battery and then crank the car. You don't need to watch it since it will capture the highest current rating and hold it for you to review after you stop cranking.
Unfortunately good DC clamp ammeters are always much more expensive than AC clamp ammeters.
How lucky were we to not have lost the whole building?
The previous HVAC person had plumbed the natural gas line to the furnace with flexible gas line designed just for this purpose. When the fire inspector saw that, he told me about how often those are compromised even in a little fire… A further inspection of the natural gas line showed it was within the last mm of being burned through in spots. Had the fire gotten a supply of fresh natural gas – it’d been all over.
Under the hood of the car, the plastic covers over the fuel rails were melted on the right side of the engine, and the OEM rubber fuel lines were visibly cracked. Had the fire gotten to the gasoline – well, you can imagine the rest.
We had to throw out so much inventory as a result of the corrosive nature of the urethane smoke! All the tools, even those in the tool box with the drawers closed, had and still have a coating of rust on them. We have tried to clean them, and lubed them up, but it’s insidious. Our lathe and mill got it bad. A new telephone in the shop, less than a month old, was destroyed because of the corrosive smoke alone. It wasn’t near the heat, it was just in the same room.
I had to throw out camshaft cores, brake rotors, calipers, used clutches, and all kinds of parts that I’d accumulated in 19 years of 928 work. We filled a steel and metal recycling dumpster.
flourescent fixtures melted and hanging from their cords The natural gas line that was very nearly breached by the fire. The corrosion ruined parts ...and coated every tool with rust
03-01-2019, 12:00 PM
