Topic: Recovering from a Car Fire: What went wrong and how to fix it!
To: Amateur racing enthusiasts
From: Team OLD FARTS,
My intention with this thread is to share with my fellow racers our team's mistakes, and how to avoid them in the future. There are also some ideas on the recovery from such an event, and possibly some useful technical information. If I am wrong, feel free to correct me. All of our team members are amateur mechanics at best, and this is probably the most invasive repair we have ever attempted. Hopefully this information could save at least one team from a catastrophic, dangerous fire. Special thanks to the fire-fighting team at Buttonwillow for quick and effective extinguishing work.
Our Porsche 924 suffered a massive car fire at the 24 hours of Buttonwillow. 8 hours in our driver came in to swap drivers. When going out, our next driver, Karl, noticed a few puffs of smoke when exiting the hot pit. Three turns later, Karl had no clutch, brakes, engine, and huge plumes of smoke escaping from the hood. You can see the video in this thread:
http://forums.24hoursoflemons.com/viewt … p?id=17063
We were doing quite well, having clawed our way from 40th to 10th, but there were a few minor quibbles: The battery indicator had been on even before the race began, and the starter was having a hard time firing the car up. We attributed this to some faulty Porsche wiring and concentrated on other things. During the race, we found the cause of our battery indicator light to be a loose ground wire, but after that we still needed to push start the car. Once going, besides a difficult idle, the car seemed fine - so we ignored the starter problem. Then this:
The fire started shortly after refueling, and melted the fuel and fuel return lines. When we pushed the car into our pit there was still fuel dripping out of these lines. This was an obvious effect of the fire, and one of the primary reasons it blazed for so long, but not a root cause. The Porsche 924/944 has a shared clutch/brake reservoir, which melted and resulted in loss of clutch and brakes simultaneously. A cursory glance shows no hope of recovery in the 16 hours of racing we have left. We call it a night
Here she is the morning after we get back:
The back of the engine (Notice the fried fuel lines leading to the fuel rail) had the most damage. We had suspected a slightly leaky fuel rail before the race, but after welding two junkyard fuel rails and swapping in a third, there was no room in the budget or time to find another. The stock fuel rail had last us some 15+ races, but after some engine work a few races ago we couldn't seem to find a workable rail.
Gross!
Intake manifold disassembled. Removing brake/clutch components. Check out that oil filler cap!
We found THIS during the tear-down. What this is, folks, is the line to the emissions control charcoal canister. To those of you unfamiliar with the device, it is a canister installed on late-model vehicles (relatively - our Porsche is a 1987 model) that captures excess fuel vapor from the fuel tank and stores it inside charcoal pellets until the engine is sufficiently warm, then the canister is redirected for burning in the engine. That's all fine and well, but what this means is that there is a third line from the fuel tank that channels all excess vapors through this hose. We pulled the canister almost from the very beginning, sometime around 2009 I suspect, for weight savings. At one point in the past, perhaps four races ago, this line was pulled out of its location in the fender well, and left venting in the engine bay, an oversight from our lack of understanding of what the charcoal canister actually did. You can see in the picture the grommet where this hose passed into the left front fender and vented these fumes harmlessly into the whirlpool of air in the fender well. This innocuous hose, when yanked out of the fender, was venting highly flammable fuel vapor straight from the fuel tank into our engine bay. How we got so far without catastrophic failure I don't know, but perhaps we needed a better spark.
Much further down the car, we find the charred remains of the fuel vapor line that once led to the charcoal canister. The fire burned this hose far further from the engine than anything else; this shot is right below the rear seats.
More tear-down. We labeled all of the harness wires, while still connected to the sensors, with blue painters tape.
Now, for no reason, my cat:
Disconnecting the wiring harness from the inside. Turns out we were quite lucky, and the main harness escaped nearly unscathed. The ECU harness was a different story. Check out the gnarly burn marks two pictures down.
The engine-less donor car that contributed its life so that ours may have a new set of arteries.
Cleaning the engine bay so that we can more accurately track down leaks in the future:
Pairing up components with that of the parts car. We got quite lucky in that we needed nearly nothing from expensive Porsche dismantlers, save a new dipstick. Check out that oil filler unit (The unit has a combined Air-Oil Seperator).
Dismantling the engine bay harness and ah hah! We have our spark. This was the factory 4AWG wire that led from the battery to the starter motor. Somewhere along its length it had began to rub against the engine, and eventually reached copper-engine contact. We expect that this shorting was the spark for our fire.
A better view of the cable I'm talking about:
Whatever the firefighters use gets EVERYWHERE and is hard to clean off, especially with water. Here it got into our mostly sealed timing belt area.
Rebuilding:
Rebuild complete! 100+ man-hours later (A substantial portion mine) two and a half weeks after our fire we have a completely-assembled Porsche engine. But will it start?
Yes!
Boy, this journey caused a mess.
Conclusions:
We should have diagnosed our electrical problem from the start. Knowing about the battery indicator lights going into the race but not fixing them was a mistake, and having to push start the car AFTER fixing the ground mid-race and having good battery voltage should have set off alarm bells. Even the spark might not have been enough on its own, but we had a combination of a possibly leaking fuel rail that should have been addressed pre-race along with the fuel vapor hose leading straight into our engine bay, with its multitudinous places for possible ignition.
If you are stripping components out of your car for lightness, simplicity, or cleanliness, make sure you know the function of the components.. Our fire came from a desire to finish competitively, a misunderstanding of certain components of the engine emissions equipment, and some simple maintenance oversights.
Hope you enjoyed our thread and please, stay safe.
Regards,
Team OLD FARTS
1987 Porsche 924 "Pac-Man"
1986 Audi 4000 Ghost 'Speedy'
1991 Audi 200 Ghost 'Clyde'
