Word of Warning from "Don't Try This At Home Productions" PART II

[uBoat Commander]

I decided to dismantle the intake spider on my 81S Euro 4.7. It was running, then it got to the point where it would start then immediately die. I assumed it was a filter/intake screen on the fuel distributer.

I took off the runners and the main intake, and the metal fuel lines were just sitting there.

I had the genius idea - I'll put a small container under each of the 8 fuel lines, I'll crank it over, and see if fuel squirts out. This way I would know if the CIS Injectors were bad or if it was a clog somewhere in the fuel lines.

Keep in mind - there is NO MANIFOLDS on the car at this point, so I have no idea how the following happens -

I turn the key.......AND THE CAR ROARS TO LIFE. I also got an earfull of the worst noise I can identify...wwwwwhhhhUUUUMMMPHHHH!!!!

And the engine bay explodes in fire.

No extinguishers in the garage.

I did finally get it out by smothering with a blanket, towels, rags and spraying with water.

I'm too f...ing upset to even take pics. First purchase I make before I even look at the car again - fire extinguisher. 40 + years working on cars, what a stupid, rookie mistake. I'm embarassed.

Thanks for being a place to vent.

[uBoat Commander]

Silver lining I guess - It IS getting fuel? Talk about looking for a positive....

[GuyS]

Crazy isn't it? Don't feel bad, we all make mistakes. I would be a little concerned about how much water got into the cylinders, besides that I am sure it was simply fuel burning.

My 79 hadn't run in 11 years. I started by turning the engine over by hand. Then I simply wanted to see if the starter would turn the engine over. The car had no fuel pumps so I wasn't even concerned that anything would happen.

Wouldn't you know it, car started on the first touch of the key. That's right, no fuel pumps and turpentine in the lines. Strange how cars behave sometimes. For all the complications, we need to be reminded that air, spark and fuel make the whole thing go bang

[Geschwindig]

So glad your only sacrifice was some towels, not your car or your life, uBoat!
Your genius idea was not in itself wrong, just backward. All the really dumb
mistakes I make are usually from forgetting to think twice about them. In this
case it should have been 3 times: Fuel-Spark-Compression. You would have then
EXPECTED that to happen. Gasoline in liquid form does not burn, it is the vapor
and oxygen above it. You wrote that the fuel lines were open, with fuel out in the
open, no manifold. Lots of FUEL vapor floating around. No manifold, combustion
chambers open, with ignition system enabled, firing SPARK plugs. Pistons pushing
anything in the cylinders out past the intake valves. COMPRESSION. How could the
whole thing NOT explode!

Don't be embarrassed, be thankful for the very inexpensive, (relatively), learning
experience. Happens to me all the time!

Kevin

[uBoat Commander]

LOL - yeah, when you put it that way. A true "DOH!" moment...

[AirtekHVAC]

Lol...sorry about the fireball....good write up tho'

Get it on video?

[uBoat Commander]

Originally Posted by AirtekHVAC

Lol...sorry about the fireball....good write up tho'

Get it on video?

I wish - it would have won "America's Funniest Home Videos"

The look on my face would have been priceless. After I couldn't get it put out at first, I ran full speed to the house & screamed for my wife to help.

Keep in mind I have not "Run" for years. Wife thought I was gonna have a heart attack. She has been making jokes all friggin night about it, no matter how many times I tell her I'm not ready to joke about it.

My 11 year old daughter thinks she is funny - every time she sees me, she asks "You smell something burning?" then she cracks up.

I think I'll drain her college fund... see how funny she thinks that is.

[Danglerb]

I don't know CI$ that well, but if injectors are working properly with no manifold vacuum would you get much if any fuel flow? Fuel rate is differential pressure across the injectors.

[curtisr]

Originally Posted by GuyS

That's right, no fuel pumps and turpentine in the lines.

Who knew?! I'm switching to turpentine instead of gas from now on.

[curtisr]

Originally Posted by uBoat Commander

I think I'll drain her college fund... see how funny she thinks that is.

And then you can explain to her what 'burn rate' means.

I've always thought that you can't teach kids enough about personal and family finance.

[924CarreraGTP]

I did the exact same thing on my first Porsche 944 when I was 16 years old. I was working on the fuel rail, and forgot to put the end cap back on. So when I turned the key fuel spilled out right on top of the distributor and it caught fire immediately. The fire extinguisher that I had would not work, so I resorted to a half empty bucket of water that was near by. It just happened to have dried paint chips in the bottom of it. I dumped it on the engine, and almost got it put out. By then my Dad had gotten the water hose, and we put it out. I had to replace all of the vacuum hoses, and of course the plug wires. When I sold the car, you could still see white paint chips down under the intake. I learned my lesson though, and now every time I'm working on fuel systems I unplug the ignition coil at the distributor. I make sure to have a good working fire extinguisher in ALL of my cars as you should in any Porsche. I also keep a flowing water hose handy just incase my other options fail. It's also smart to move all of your other cars out when you're working on fuel systems. A car fire is one thing. A car fire that burns your garage down with all of your cars in it is another. Sorry to hear about it. Accidents happen, and the old motor will probably be alright after you get the burnt parts replaced.

[Danglerb]

Originally Posted by 924CarreraGTP

I learned my lesson though, and now every time I'm working on fuel systems I unplug the ignition coil at the distributor.

Spark voltage starts at the coil, and any part of the system from the coil high tension connection to the plugs can make a solid spark. It might be safer leaving the distributor connected and prevent spark with some other method.

[924CarreraGTP]

To explain better, I usually unplug the distributor and pull the wire over to the coil and tuck it in behind it. Sometimes I unplug from the coil. It all depends on the area that I'm working on. On my 911 I cannot do that at all because the Constant Discharge Ignition (CDI) will fry if you don't have the coil plugged in when you attempt to start the car. So it's different from car to car.
One time I was working on a fuel pump under a car and didn't realize that I was spilling fuel onto a burning shop light. I grabbed it, and quickly threw it out of the way. The bulb burned out when I threw it and it did not catch fire, but it was still a good scare. Another thing to be careful about. Don't spill fuel on shop lights.

[qdac]

I don't have a CIS car, so please verify these statements.

My understanding is that CIS sprays fuel CONTINUOUSLY as long as the system is under pressure. This may be occurring the entire time that the fuel pump is running. The amount of fuel being sprayed varies along with the position of the sensor plate (that big plate in the air path.) I do not think that the engine has to be turning to dump fuel into the cylinders - the system just has to be under pressure.

The book "Bosch Fuel Injection & Engine Management" describes the CIS K-Jetronic system in some detail & may be useful in your restoration efforts. There is a lot of diagnostic info in the book.

[Danglerb]

I'm not a CI$ expert, but pretty sure its differential pressure across each injector that sets flow. Fuel pressure regulators make the input to the fuel distributor track manifold pressure (constant base differential pressure) and the FD combined with the WUR regulate the pressure at each injector.

I am not certain, but pretty sure below some minimum differential pressure flow totally stops. Reason for this belief is that Porsche keeps the fuel pressure up even with engine off to keep the boiling point of the fuel above the high under hood temps to avoid vapor lock.

[rjm65]

Originally Posted by qdac

I don't have a CIS car, so please verify these statements.

My understanding is that CIS sprays fuel CONTINUOUSLY as long as the system is under pressure.

You can jumper the fuel pump, which pressurizes the system, and the injectors won't do a thing, no fuel will come out of the injectors (otherwise our CIS engines would flood every time we jumpered the fuel pump to check/adjust the control and system fuel pressures). With the fuel pump jumpered and engine off, if you manually push down on the airflap (normally airflow causes this movement), you will move the piston inside the fuel distributor and this will cause fuel to flow to the injectors. You'll hear the injectors buzz when this happens. The more you move the airflap down the more fuel that will flow to the injectors. How much the airflap resists movement from the airflow during operation is determined by the control pressure (set by the WUR). Increasing the control pressure will lean the mixture, decreasing control pressure will richen the mixture. Make sure you have a set of fuel pressure gauges before tinkering with any of the pressures or you'll never get it right.

You want to be careful about this as doing the above is spraying fuel into the cylinders and you don't want to flood your engine or let so much fuel flow into the cylinder that you run the risk of hydrolock.

I had a thread over on MPDano's site with a little more detail on CIS stuff.

Porsche 928 Forums dot com - View topic - CIS Warm Up Regulator Made Simple

[Landseer]

Ouch. Sorry to hear this. Am hoping any damage was cosmetic. If more than that, I'm certain you can find suitable parts or a new shell. Don't give up.