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1986 930's Avatar
 
Join Date: May 2011
Location: Cape Canaveral Florida
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Dieseling on shut down

As far as I know I have a stock CIS System, Euro Fuel System. After running the car for a bit, the car diesels when I shut it down. ( turn off the key and it continues to run for a bit, very roughly) When I run the car around town and start and shut it down it only does it on the first shut down. Otherwise it runs great. So I have two questions:

1) What is causing this?

2) Is this bad and I am destroying my car little by little?

Thanks,
Mark

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Mark

1986 930 Ultra-Smith RUF Slant Nose conversion, RUF VB, K-27 HF-S, B&B Headers and Exhaust, RUF Short Shifter, RUF Interior
Old 06-12-2011, 04:08 AM
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beancounter
 
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There is something called the ignition delay relay. This maintains power to the ignition system for a few seconds after you shut off the key. The fuel pumps power is cut, but the car runs on for a few moments to burn off the last bit of fuel in the injection system. From your description, its possible that what you are calling dieseling is actually the normal ignition delay.
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Jacob
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Old 06-12-2011, 04:59 AM
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It could be the injector(s) not holding pressure enough after shutdown and leaking.

Check your fuel pressures. Raising the system pressure can stop it occuring however if it isn't the usual delay-relay shutdown then more than likely a leaky injector.
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Ben
'85 930 - Black on Black
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Old 06-12-2011, 05:26 AM
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Thanks for the replies.

If the injector(s) were leaking, wouldn't I smell fuel?
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Mark

1986 930 Ultra-Smith RUF Slant Nose conversion, RUF VB, K-27 HF-S, B&B Headers and Exhaust, RUF Short Shifter, RUF Interior
Old 06-12-2011, 08:40 AM
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Crotchety Old Bastard
 
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No you won't smell fuel because they are leaking into the cylider. The delay relay is in place to allow any unburned fuel to do so, meaning that if the fuel system is working perfectly there will be no run-on.
Unfortunately the only way to find a leaker is to pull the injectors and test them. If this is not something you want to do the relay can be jumpered/disabled. There has been a few threads on this phenomenon lately and one has the ID# for the relay and which ports to jump.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 06-12-2011, 10:41 AM
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Is it something to worry about beyond just annoying?

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Mark

1986 930 Ultra-Smith RUF Slant Nose conversion, RUF VB, K-27 HF-S, B&B Headers and Exhaust, RUF Short Shifter, RUF Interior
Old 06-12-2011, 11:15 AM
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