Auto Igniton

[dypascal]

Hi,when I Turn Off The Engine On My 964 Turbo,the Engine Continuous To Run For 2/3 Seconds Before Shut Down.any Idea About That?many Thanks

[Flieger]

Turbo timer?

Maybe there is a turbo timer electronic system installed by the previous owner (or Porsche factory- I don't own a turbo) that keeps the engine running after turning off the key. This keeps oil circulating and helps lessen oil burning and coke build-up in the hot turbo housing and helps oil system longevity throughout the lines, filter, and engine.

This is a desirable condition if the motor is not "Dieseling"

If it is "Dieseling", check for carbon buildup in the combustion chamber on the heads, valves, and pistons, and spark plugs. The carbon can shrink the chamber, cause detonation due to increased compression ratio and hot spots. The carbon holds heat in the cylinder, causing detonation like a glow plug in Diesels. To cure this, take the car out at night and run it up and down to redline under load and engine braking through the gears. It will smoke and cough out the carbon. "an Italian tune-up"

Also, your spark plugs may be too hot in their heat range. Maybe a colder plug, like the factory reccommended for early turbos, would be better. If you drive your car agressively, the plugs need to be cooler so that they do not stay hot and cause detonation.

Hope this helps.

[dypascal]

Hi Flieger Thanks For Your Help.i 'll Try Colder Plugs But I Think My Nozzles Could Be The Problem.any Tips About This?

[Flieger]

If you suspect dirty fuel injectors, run a bottle of commercial fuel injector cleaner through the system in a full tank of fuel.

Symptoms of carboned injectors would be popping/sputtering at low rpms and off throttle and poor throttle response. Full throttle running should be pretty much normal because the higher pressures and volumes of fuel will overcome dirt resistance. I would not expect the injectors to continue to spray fuel after the fuel pressure is removed, but they may hold a little residual pressure if they are very dirty. It is a cheap treatment (relatively).

[RarlyL8]

when I Turn Off The Engine On My 964 Turbo,the Engine Continuous To Run For 2/3 Seconds Before Shut Down

It is supposed to do that. The fuel pumps stop and excess fuel is burned off before shutdown to prevent subtle backfire or "poof". It has not done this all along?