Engine fire - how lucky was I?

[RichMason]

So I was going to move my 911 into it's new garage last night. Turned on the key, pulled on the defroster/cold start for a second to activate the cold start and it cranked right up. Ran for a second, sputtered and died. That's odd, never happened before. Maybe its really cold so I went through the procedure again but it just turned over with no effort to start. Got out of the car, saw smoke, smelled burning plastic and ran for the fire extinguisher. Smoke dispersed quickly but the left side of the air cleaner housing was hot so I pulled it off and beheld my melted and smoking MFI stack. Looks like the cold start fuel ignited to some degree but it went out quickly. How lucky was I? I've disconnected the system but I'm still concerned about the source of ignition...is this common? I didn't hear a backfire but I changed the cam/MFI seal this weekend so the pump timing may be off one notch. Could this be part of the problem? Finally, I need to replace the stack...should I keep the plastic or replace them all with metal and where can I find them?

[john walker's workshop]

lots of MFIs went up in smoke because of a fire from the raw gas squirted in by the cold start system. if you think you have a fire, the best thing to do is get the engine started so the fire is sucked down the holes. it's fairly well contained by the air filter housing so you have some time.

[69911e]

I did the same thing with the defrost switch(now changed to a momentary push button). Don't squirt fuel unless the engine is cranking, the moving air keeps the fuel vapors in the intakes. Keep cranking for a few seconds after releasing the button if it fails to start. 15 years of no problems doing it this way.
ED

[Early_S_Man]

Rich,

Sounds like you were pretty lucky! My recommendation would be to tape off the cold-start solenoid wire temporarily, until you can replace all of the hose with OEM-type fabric-braided fuel hose that Pelican sells, or any VW, Mercedes, or Porsche dealer should have in stock. Don't use a generic hose from Autozone or a like source!

[cosmo]

I've been the auto repair bussiness for over 30yrs and I've never seen so many engine fires. Whats up with Porsche??

[Doug Zielke]

Congratulations, Warren and Phyllis!!

[Jim Sims]

Originally posted by cosmo
I've been the auto repair bussiness for over 30yrs and I've never seen so many engine fires. Whats up with Porsche??

Air cooled cars up to 39 years old; many with original fuel lines and fittings and original wiring harnesses. MFI and CIS fuel injection systems with many fuel lines. Time, temperature and vibration take their toll. Fires are inevitable. '64 Fords and Chevrolets with original fuel system components would likely be burning too. Cheers, Jim

[cosmo]

Sorry but thats no excuse!! In early 1970's 914's caught fire on a regular basis.

[pwd72s]

FWIW, it wasn't just MFI cars...I had a fire in my then nearly new '70T....the mickey mouse cold start sytem of tubes that squirted fuel mounted in the upper part of the air filter housing. NOT one of Porsche's better design ideas. I notice the tubes aren't there in my '72. Warren or John, do you know when the factory dropped the hazardous system?

[Early_S_Man]

cosmo ... as did Pintos, Vegas, even some Mazdas and Datsuns ... when smog-controlled underhood temps surpassed the fuel-retension capabilities of new production cars!

[cosmo]

All I'am saying is take alook on the net at some of the larger Porsche salvage dealers and look how many engine fire cars they have, compaired to other makes it's scary!!

[RichMason]

It seems to be a design problem. The hoses are new, the lines in the air filter housing are clear and the car rarely, if ever, backfires. While the wires may be old, nothing frayed and grounded to cause the ignition - it was pure fuel and whatever magic takes place inside the MFI intakes.

There may be an issue of incompatibility of the parts - if the 72 and later cars didn't have this system with the metal lines in the air cleaner that drip fuel into the stacks (my car is a 69 E 2.0 with the correct air cleaner housing), then the plastic stacks (which I was told in another thread are for the 2.4 S matching the pump on my car) may be the weak link. Maybe it was a chemical reaction instead of a fire or maybe the plastic is more prone to ignition with a backfire?

[RichMason]

I just spoke to my local Porsche shop and it looks like there were several different systems. The later cars used "injectors" lower down in the air cleaner housing so that you were sure that the fuel went straight down the throat instead of dripping down the side of the stack.

[john walker's workshop]

a bit of carbon gets stuck between the intake valve and seat, a flame leaks upward thru the little gap, lighting off the fuel from the squirter. it's a normal occurance in lots of cars from day one. carbs have squirters, as well as that MFI cold start system. newer 911 CIS FI systems still blew airboxes because of the same thing. they're starting to get a grip on the problem with DME, which doesn't use a cold start injector, and has an enclosed intake manifold. once the engine is running, any small flame gets sucked down the intake and extinguished.

[kristian85]

Originally posted by cosmo
I've been the auto repair bussiness for over 30yrs and I've never seen so many engine fires. Whats up with Porsche??

Actually, engine fires are very common in all Porsche models using combustion engines.

[Dantilla]

I bought my '73 from an insurance auction. Nice clean car except for the crispy engine. Perfect candidate for the 3.2.

[mskala]

Originally posted by cosmo
Sorry but thats no excuse!! In early 1970's 914's caught fire on a regular basis.

The 914's had a specific problem which was addressed by factory recall. Except for that, the only 4-cyl 914 fires I ever knew about were from people who converted to carbs and from replacing high-pressure fuel lines with crap vacuum lines.

The 6-cyl 914's are the same as the 911T's, where you had to disconnect the start enrichment mechanism that shot raw fuel the sometimes started fires.
Mark S.
'70 914-6

[pwd72s]

Originally posted by RichMason
I just spoke to my local Porsche shop and it looks like there were several different systems. The later cars used "injectors" lower down in the air cleaner housing so that you were sure that the fuel went straight down the throat instead of dripping down the side of the stack.

Actually, not lower down in the air cleaner housing...but into the stacks themselves, approx. half way down...assuming my car is standard '72, which I'm sure it is. After the experience I had with my 1970 911T, I would suggest dumping any cold start system that uses those in the air filter housing lines. They are a disaster waiting to happen, and I'm amazed they are still around. Does anyone know if the later stacks are still available as a new part?

[sammyg2]

I'm one of those junk yard rats who like to frequent Pick-a-part junkyards.
Every time I've been there I see several Chrysler 2.2 liter turbo engines that are burned up. Caravans, LeBarons, etc. Seems they thought it was a good idea to put the rubber fuel injection hoses directly above the turbo. I would have enjoyed being at the meeting where they approved that one.

I'm on my 4th porsche and never experienced a fire. I don't personally know anyone with a Porsche who has experienced an engine fire. They don't seem to be that common to me, but any time you have rubber fuel lines on top of an air cooled flat engine you run the risk of a fire. Think about it, on a V8 a fuel leak will run off the front or back of the intake manifold, down the block and onto the ground. No ignition unless it hits the exhaust.
same with a V6, an inline engine would be even safer except for those genius' who put the exhaust manifolds directly under the intake. The vapors will probably not get concentrated enough to be ignited by a faulty ignition system for example.

On a flat air cooled engine the fuel puddles on top of a hot engine and vaporizes. By design it doesn't have anywhere to go.
All it takes is a small spark and it's lit up. Plus as someone stated most of these hoses are getting very old.

[cosmo]

Well for all who want to argue, I currently work for and have for 10yrs a car manufacture and have never seen a engine or for that matter any fires anywhere on the car.So it's very possible to build cars that don't catch fire, reguardless of the fuel system.