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'79 n/a engine overrun at shut off, feedback requested

 
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porsche_reg  



Joined: 19 Jun 2016
Posts: 53
Location: Boise, Idaho

PostPosted: Tue Apr 11, 2017 12:21 pm    Post subject: '79 n/a engine overrun at shut off, feedback requested Reply with quote

Hey all - I have a "overrun" or final rundown of the engine when I turn it off. As I've known this car for it's life, I can say that growing up it was something I thought was a normal quirk, but I'm not finding any of the usual messages to that end on this forum.

Somethings I've noticed:

1. It seems pronounced or more likely if I've been running the engine hardish before shutting down. I'm mostly dd run down six miles to work in a near straight line (some twisties, but don't need to slow down) in 3rd gear, 40 - 50 mi at 3 - 4k for the 15 minute run.
2. I've been noticing a few broken lines in the vacuum system that I've been fixing - anything related? Years ago my dads mechanic unhooked the egr and it's been that way for many years.
3. Although I don't currently know much about the engine timing, could it be related? In the fall I took her in for some work and the shop noticed the timing was way off. I haven't been playing with timing, yet, so not sure if related.
4. I run the VT hard motor mounts (was just reading an article on these, I'm sort of thinking about looking for something else due to the harshness) would there be a possibility of rattling this thing apart? Related to timing or similar?

thank you for any info!
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Paul  



Joined: 02 Nov 2002
Posts: 9348
Location: Southeast Wisconsin

PostPosted: Wed Apr 12, 2017 9:54 am    Post subject: Reply with quote

Some possible causes:

leaking injector(s) and a hot spot in or more cylinders
leaking cold start valve and a hot spot in or more cylinders
faulty ignition switch
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
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Ozzie  



Joined: 12 Mar 2005
Posts: 4416
Location: Townsville, Qld. Australia

PostPosted: Thu Apr 13, 2017 7:51 am    Post subject: Reply with quote

Correct me if I am wrong but wasnt there a tech bulletin by Porsche about this and mentioned installing a diode somewhere.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
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porsche_reg  



Joined: 19 Jun 2016
Posts: 53
Location: Boise, Idaho

PostPosted: Thu Apr 13, 2017 9:54 am    Post subject: Reply with quote

Eager to hear more on this... thanks!
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'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback
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porsche_reg  



Joined: 19 Jun 2016
Posts: 53
Location: Boise, Idaho

PostPosted: Sat Apr 15, 2017 6:32 am    Post subject: Reply with quote

Another thought and question, could non-ethanol 87 octane cause this type of issue? I'm a little confused on the gas topic. Recently read about another '24er who was switching back over to 91 oct, I'm using the non-ethanol as I put $1k into new hoses and ~$500 into tank seal over the last few years.

thx
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'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback
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Ozzie  



Joined: 12 Mar 2005
Posts: 4416
Location: Townsville, Qld. Australia

PostPosted: Sat Apr 15, 2017 8:03 am    Post subject: Reply with quote

I use 95 or 98 non ethanol
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance
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porsche_reg  



Joined: 19 Jun 2016
Posts: 53
Location: Boise, Idaho

PostPosted: Sat Apr 15, 2017 8:56 am    Post subject: Reply with quote

hmmmm, have not seen that octane around my parts (Boise, Idaho).
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'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback
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