Distributor cap pitting on terminals
03-22-2008, 02:57 AM
#1
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Distributor cap pitting on terminals
I've been chasing an intermediate miss at idle, and noticed a lot of pitting on the brass terminals inside the distributor cap, even after changing it recently. Other things I've done around the same time are; changed wires, plugs, cap rotor, cap gasket, new ground cable and cleaned up ground points, changed alternator regulator (several years ago), checked timing marks (dead on), did AFM wiper retracking procedure, new O2 sensor, coolant temp sensor, TPS, cleaned reference sensor connectors. Also noteworthy, is that the spark plugs seem to get carbon fluff on them quickly. Fuel pressure is perfect. Only known issue is a weak battery. My thoughts at this point are; weak battery causing resistance, coil going bad, DME unit??? Carbon on plugs usually means running rich, but I think the cause is electrical (weak spark?) because the fuel pressure and injector leak down tests were normal. Thoughts?
--Lizard
--Lizard
03-22-2008, 11:42 AM
#2
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I'll ask my failure analysis prof about the pitting on tuesday- corrossion is his profession.
Battery with low voltage will definitely put a stress on your system with all that current it will be flowing, though.
Battery with low voltage will definitely put a stress on your system with all that current it will be flowing, though.
03-22-2008, 05:38 PM
#3
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Knfeparty-thanks! I'm just wondering if there's some excessive arcing going on inside the cap due to resistance, timing, or high voltage issues. After all of the other work I've done, I'm really leaning towards the DME throwing off the injector timing a little (reason for frequent carbon fouling of plugs) and possibly doing the same thing on the distributor timing?? Strange part is that there are no drivability issues, other than the slight miss at idle.
--Lizard
--Lizard
03-25-2008, 11:22 PM
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He said that definitely sounds like arcing. Capacitors going out and letting too much current flow all at once contributes to arcing, as well as the timing to the rotor being a bit off. I don't know what controls the ignition timing in a 944, though.
Hope that helps.
Hope that helps.
03-26-2008, 04:47 AM
#5
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Thanks Knfeparty. My timing marks line up perfectly. My only options left are the DME or possibly a 22y/o coil, but I'm not sure if even a bad coil would cause this. I'll post back if/when I find the problem. Thanks for taking the time out of your day to look into this for me!
--Lizard
--Lizard
