Wow! Cis Meltdown?

[Porschephanatic]

Strangest thing happened to my wife and I yesterday. I'll make an honest attempt to be brief, but this is baffling!
Scenario: Engine run for over an hour, temperature normal. Cruising at 2500 revs, the engine just dies. Before I could even disengage the clutch, there was an explosion out the dual outlet Dansk (like a shotgun blast), then as I pushed the clutch pedal in, there was a huge cloud of white smoke out of the engine lid grill, while simultaniously there was the awful sound of very loud detonation (like run-on when an old Chevy's ignition was turned off, only much louder), then silence. Of course, after the shock factor had subsided somewhat, I tried to restart the engine
to no avail. I had good, hot spark, so I pulled off the air filter. I lifted the pop-off valve, and was amazed by the amount of fuel vapor being emmitted from through the valve, around the airflow sensor plate, and shortly thereafter from the tailpipes.
Fortunately, we were only a mile from home, and had a ride in minutes. I let the car cool for an hour, and it started as normal and I was able to drive it home. It still has excellent power and response (for CIS injection).
Where do I start now that it runs fine. Anyone else have a similarly traumatic experience? Thanks in advance. The membership of this site has never left me down!

[Porschephanatic]

Sorry. Forgot to mention that during my initial roadside diagnosis, I thought the thermal time switch may have failed, resulting in the cold start valve being energized, causing the flooding condition, so I pulled the wires off, w/ no change. Then I pulled off a wire to the throttle-closed position switch, thinking this may control a deceleration valve, with again a no-start condition. It sounded as though it wanted to fire while cranking, though. Thank you. Hope this helps.

[tutzilla]

Sounds similar to the problem that I had with my 81SC except without the loud explosions. Car would run fine for a specified amount of time and then just die and then would not start. I let it cool down overnight , started it the next day and the same thing all over again. Turned out to be the CD Box. Maybe this will help you!

[911mot]

Sounds like severe pre-ignition. Could well be CD box. I've seen similar stuff happen when a condensor goes bad in a points setup. Blew a massive hole in an exhaust silencer on the M25 in a Capri once when a new one failed. **** the life out of me!!

Also check the spark plugs for signs of overheating as well. If the tip of the plug gets too hot the fuel burns under compession before the spark moment. Thats what causes running on after igniton switch-off and the diesel-like sound and the white smoke from the intake.

Causes of overheating could be running too lean, incorrect ignition timing, or something like a shop rag blocking airflow to cyl heads

[bigchillcar]

i was thinking about ignition timing as well..not sure if severely retarded or advanced ignition would be the one to cause this symptom. has the timing been adjusted recently?
ryan

[Porschephanatic]

Thanks for responses. The car just had it's 75k service, but it could be timing. I'm beginning to believe your ignition theories. I've read through some archives and fuel injection components appear to completely fail (generally speaking) instead of intermittently failing only after the engine is completely warmed up (but not screaming hot). CD box is a (second ) Perma-tune (every 3 or 4 years, guys?). The first Perma-tune completely failed all at once, and cooling down didn't help. I should just bite the bullet and buy a Bosch CD box @ 4(?) times the price. If the Bosch unit lasts 4 times as long, it will be well worth it! I'll go out and check my fairly new spark plugs and let you know what I find. Thanks again!

[bigchillcar]

if you have an old bosch box, they can be rebuilt much cheaper...also try searching the used parts threads on here..you might find a deal. good luck!
ryan

[Paulporsche]

A lot of posters have said their Permatunes stopped working once warmed up, causing similar symptoms. Someone even put ice on his and the thing worked again, only to quit once it got hot again.

[bigchillcar]

i'll second paul if i didn't mention that fact as well..lots of questions out there concerning warm permatunes and intermittent problems..
ryan

[pa911]

When my Permatune started going bad car would just die when I tried to restart seen smoke then the BIG BANG! I don't want to hear that noise again I have a Bosch now!

[Porschephanatic]

Checked my plugs, and they look good. Maybe not enough usage yet to show symptoms. Just read another thread on CD ignition box failures. Anybody have any luck with the MSD 6-AL system with tach adaptor? The "BIG BANGS" can't be good for the old gal! I'm gonna check our hosts' inventory now. Thank you all so much!

[Porschephanatic]

Wow! Now I'm really confused. Does the MSD system Wayne sells replace the piece of crap Perma-tune or piggy-back it? Wayne doesn't even carry any Perma-tune products anymore. What part #'s do I order (box and tach adaptor)? Sorry I'm so naive about ignition systems. Thanks again!

[Bobboloo]

The MSD is a replacement. It is an improvement in some ways over the Bosch in that it gives off multiple sparks below 3k RPM to improve idle and low rev running. They are bconsidered the best alternative to the Bosch CDI.

[ruf-porsche]

Ask Art Z about his Perma Junk.

[tshih]

Wow, do you have a pop off valve installed to protect your airbox? Sounds like a flooded engine with all that extra fuel which prevents restart when hot.

[Porschephanatic]

Yes, Sir! Pop-off valve was fortunately installed years ago. Previous owner installed a brand new airbox without it, but I learned enough from you gentlemen to install one immediately after I purchased my SC. New MSD-6420 now on the way!