1989 Carrera 3.2 engine "dieseling" upon shut down

[xxultramistersi]

Greetings Late Night Readers,
My car seems to be having trouble shutting down. After I turn the car off it seems to sputter for a few seconds as if trying to start itself up again. It doesn't sound like the car is enjoying it at all and it takes an extra second to start up again after it happens. Any suggestions as to how to diagnose and fix this problem?
Andrew

[Tippy]

You might have a leaking injector.

Second, more than likely the carbon build-up on the pistons is acting like an ignition point and when the fuel leaks out of the injector, it is ignited causing dieseling.

[db_cooper]

Interesting problem..when the ignition is off..the DME relay should shut down..and no fuel injector pulse and no spark.

Yes..it could be a leaking injector. The engine needs fuel to diesel with the key off.

I would swap out the DME relay under the seat with the spare DME relay you must have available at all times in the car..use a known good one if you don't have a spare.

Try that first.

Then inspect the injectors for leaking.

Be sure your spark plugs are the correct heat range too..not likely..but you may be working under the rear deck lid anyways, if the DME relay is not the fix.

[Rob T.]

Hello from Germany

I had the same problem a few years ago.
Take a look at your regeneration valve for the activ carbon filter.
When the valve isnt thick the engine takes fuel out of the activ carbon filter and starts "dieseling"
Sorry for my "perfect" english.

Greetings Rob

[db_cooper]

Originally Posted by Rob T.

Hello from Germany

I had the same problem a few years ago.
Take a look at your regeneration valve for the activ carbon filter.
When the valve isnt thick the engine takes fuel out of the activ carbon filter and starts "dieseling"
Sorry for my "perfect" english.

Greetings Rob

Ach, du Lieber! Augustine!

A very, very good suggestion..it would allow fuel vapor in the intake manifold and your engine would diesel..

Very easy test..prior to pulling the injectors....just remove the breather hose on the backside of the airbox and plug it. See how it goes after that.

I don't know if we can still get the "purge valve" referred to from Porsche.

[xxultramistersi]

Thank you for all your help, I am sure that one of these problems will point me to the right solution. I am always so amazed at the level of automotive knowledge on this forum, keep it up and keep people like me on the road!
Andrew