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RarlyL8 RarlyL8 is offline
Crotchety Old Bastard
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Join Date: Jan 2000
Location: Huntsville, AL
Posts: 14,357
Follow up to the story, the car has been sitting sense the relay was changed out as I haven't had a chance to take 'er out for a romp. Took some time today to do that and verify everything is OK.
Well it's not exactly OK and again the gages tell the tale. Car fired right up and the AFR's and fuel pressure rose as they should over time as the engine warmed. Typically I just get it and go but this time I wanted to observe the entire warm-up cycle. Once the fuel pressure reached 53psi the AFR is usually 13.0:1, this time it was 12.5:1. That's odd. So I got out the little allen wrench and cranked the idle mixture screw until the AFR raised to 13.0:1. At that point I heard a slight miss and random pop out the tailpipe. It sounded like a lean pop. After thinking about this for a second I realized it was a lean pop and lowered it back to 12.5:1. I'm pretty sure what has happened is the plugs have fouled causing a slight miss and rich reading due to incomplete burn.
I went ahead and took 'er out for a drive, sounded really good off idle but I could hear a slight miss at even cruise. AFR had dropped from typical 14.3 to 13.7. Got to a good spot and stomped it to blow all that leftover carbon and fuel out and WOW, what huge plume of smoke blew out when the boost hit! Repeated again and the smoke was gone. Took 'er home and at idle there was a distinct miss. Looks like new spark plugs are in 'er future. Not really unexpected, could have been worse.
So one more thing the AFR gage can tell you, fouled plugs!
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 02-11-2017, 03:36 PM
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