Engine "Run On" Condition
 

Does anyone know what would cause the engine to run for a second after I turn the key off? I have done some tweeking of my fuel system and for the most part everything is great, but this problem has surfaced within the past week or so.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Bill,

Not sure if it applies to P-cars, but in my experience, it is usually caused by timing that is too far advanced.

Good luck,
Mike 94 C2 cab

That's exactly what a friend of mine said too. This couldn't also be caused by a bad coil could it?

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Could also be caused by a high idle. Condition worsens when the engine is hot or the outside temp is hot, or both.

I do have my idle rpm set a little above what the manual recommends. I'll adjust it a little bit tonight and see what happens.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Something inside the combustion chamber is getting hot enough to ignite the gasoline when the pressure, during the compression stroke, gets high enough. It could be a shard of metal sticking out, but probably not. It is probably your spark plug electrode.

Be sure your timing is not too far advanced. DEFINITELY use a higher octane gas if possible. I believe you can also use a cooler plug to try to remedy this. This condition, "pre-ignition" or "surface ignition" is bad. It is probably causing a 'knock' whether you hear it or not. It can melt pistons and it can also bend connecting rods during the 'dieseling' after shutoff.

Not trying to alarm you, but this condition should be remedied soon.

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'83 SC

All of the things that have been mentioned, but also a lot of carbon inside the combustion chamber can cause this. Give your motor the Techron or Swepco 503 treatment along with a very spirited highway run, and blow out the crap. And one other thing....are you sure the spark plugs are of the correct heat range for your motor?


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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

Along with the above, I think it might be a manifold-type vacuum leak. Then perhaps the vacuum leak was compensated with an overly rich mixture...

(shot in the dark)
.02

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Nick Hromyak
'85 Carrera

Bill,

Adjust your idle speed to 900 rpm, then see if you still have the problem.

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Warren Hall
1973 911S Targa

Hello

If you have a Marrelli Distributor then check your timing.
MFI or Carb ?

Grüsse

Warren,

Do you recommend a 900 rpm idle speed? Also, I used 89 octane with my last fillup. Should I use 93 octane? I don't think I need it. I think my compression ratio is 8.5:1 or 8.6:1, so I don't think 93 octane is needed. What do you guys think?

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Bill,

Yes, 900 rpm is the factory recommended idle speed.

And, regular 87 octane gas was the specified fuel for the 8.5:1 '72 model 911S and your '73 spec engine! Factory MFI fuel injection publications stress that drivability problems can be traced to the use of Premium fuel ... because it was/is harder to ignite!
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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 04-08-2001).]

"Regular" gas should be fine for your engine. "Dieseling" at shutoff does mean that something in your combustion chamber is getting too hot. Again, probably the spark plug electrode.

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'83 SC

I have been running 89 octane, but G&W Motorworks told me to run premium. I just started having the problem within the past few weeks though. It doesn't happen all of the time, but it is annoying nonetheless. I'll adjust the idle speed as soon as I can and let you all know what happens.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout