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I haven't had a chance to write this up and put up photos, and a few people have asked to see photos of what I did to make this work, and solve my misfire issue:
At SOC I had my car set to run at the dyno day, only to discover that I had developed a nasty misfire under boost in the weeks leading up to the convention. I have one of the factory knock detecting tools, with the LED built into it to alert when the knock detection circuit is activated, and operating to help diagnose issues with the APC.
It lit up like a Christmas tree that got invited to a Kwanzaa party when on the throttle.
While there, I tried pulling timing, and put in a higher pressure FPR, but misfire didn't go away. I was able to isolate it to an ignition problem, rather than fuel. In my car I have a large FMIC, with aluminum tubes plumbing it. I was able to keep the A/C, by tilting the radiator and A/C condensor back towards the engine, which doesn't leave much space between the radiator and the front of the engine.
My alum intercooler tubing was running so close to the distributor cap, that under boost when the resistance across the plug gap increased sufficiently high (about 14-15psi) the spark energy would arc from the end of the plug wire to the grounded metal intercooler tube!
I put some rubber insulation between the wires and the tube, and moved the tube a little farther forward, but couldn't completely get rid of the misfire.
Until.....
Walter Wong suggested I just try an NG900 non-turbo distributor cap, which has the terminals hooked at 90 degrees to the axis of the distributor, rather than having them come out the ends like usual. It clips right on, and moved the plug ends well away from my FMIC plumbing that misfire went completely away.
The car is now holding 20-21psi of boost with a base timing of 19* BTDC retarding to 8* BTDC at full throttle, and I put the 2.5 BAR regulator back in (with JSP stage 2 ECU and 34 lb. T5 431 injectors). No blinkies on the knock detector, and the car runs awesome. The different dizzy cap looks kind of cool too, but something to keep in mind if anyone needs a fix for clearance in front of the distributor.
I am going to try to get it on a dyno this week, there's a nice shop around the corner from ours I'm going to try to work with for any custom ECU work, and testing new components.
Best,
Drew
posted by 75.28.6...
Picasa album of NG dizzy cap on C900
, Wed, 23 Sep 2009 19:20:27
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