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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
--930's have a reputation for burning pistons. Many have wanted to blam this on the design of the intake manifold because it dose not test for even flows on a flow bench. Under boost I suspect this is not as big a deal. However, CIS is sensitive to varnishing and needs to be clean to work properly. If we had carbs, we could have probably had them partially or fully rebuilt every 5 to 10 years. However, with CIS we seem to think that is not necessary or they are above that. My bet is it is the head that is responsible for a high percentage of the failures.

Look at the numbers I calculated based on one injector being 10% less and another 13% less. If you though your AFR was 12.5 at 6000RPM the car would have actually been running with about 4 cylinders at 12/1 AFR and the weak cylinders at 13.3 and 13.8. That will cost someone a cylinder or two on the track quickly. This is why we typically want to run a litter richer mix than the EFI guys do. For a little insurance.

I would think the procedure might be:

Test with injectors in place for quantity and watch to see if all have a spray pattern.

If any do not spray, send injectors out for cleaning and balancing.

Retest in place. Adjust as necessary.

If unable to get them balanced attempt to run professional fuel injector cleaner through head.

If still not matched, send head out for rebuild.

Retest rebuilt head in place.

Old 03-12-2009, 07:53 AM
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