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Join Date: Mar 2007
Location: Williamsburg, VA
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Soot on a plug

I have an 1982 930 with SC cams and a twin turbo system. # 4 spark plug is covered in black soot, and after cleaning it, 3 - 4 miles of driving causes it to be covered again. I swapped out the spark plug, distributor cap, rotor and plug wire as well as the fuel injector. No change. The other 5 plugs are fine. The compression is even on all cylinders. Can the problem be in the mixture control unit? Any suggestions? (I have a little bit of oil spread in the intercooler due to a turbo scavenge pump issue, but that has been fixed.)Thanks Thor
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Old 03-18-2007, 04:29 PM
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Strange! Maybe do a leakdown test on that cylinder? If you've swapped out all other components, then the only thing I can think of is a suspect leaky cylinder
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Merv
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
Old 03-18-2007, 06:34 PM
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Iamchappy posted this link in different but related thread: http://www.pelicanparts.com/techarticles/rice_ramblings/rice_ramblings-4.htm

It's worth reading the whole thing, but in the first paragraph it says they ARE black and sooty.

Now, my 930 is stock with the W3DP0 plugs. I just removed them and they were ALL black and sooty. But this is normal.


What plugs are you running and what is the gap? Maybe this plug isn't gapped correctly. Dumb question, but are all the plugs and the gaps the same, because you said you swapped it out?

Possible fuel injector issue?
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Old 03-19-2007, 04:26 AM
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I had a similar issue and it was due to a bad injector.

I removed all 6 and had them checked / cleaned. That one ended up needing replaced. Since then I haven't had a problem with that plug.

You might want to check for an air leak as well. See if the bolts on the manifold have come loose at all. I had that problem on a Carrera a while ago.

Last edited by David G; 03-19-2007 at 01:02 PM..
Old 03-19-2007, 08:22 AM
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Wouldn't an air leak in that cylinder indicate a LEAN condition, due to unmetered air entering the cylinder?
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Merv
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
Old 03-19-2007, 02:43 PM
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