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Porsche 935 Porsche 935 is offline
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Join Date: Dec 2013
Location: Spring Hill, Florida
Posts: 457
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Air/Fuel changes

Maybe some guys can give me an insight to my recent Air/Fuel changes. Over last year and a half I wanted more power(who doesn't). I upgraded my turbos to twin 54mm. I upgraded to 96lb injectors and swapped out the 4 Bosch pumps with a aeromotive single pump(good for 1000 hp). I installed a new wide-band O2 in the exhaust pipe as designated by the manufacturer. According to the O2 car was too rich to register everywhere in the map table. Started taking out fuel. Got to the point where all fuel ratios looked good except O2 reading rich at idle(10.6-1) and too rich to read over 19lbs boost. Idle did not change much no matter what I did. But started pulling more fuel out of high boost. I live in Florida and most test days were in the upper 80's- mid 90's. It is now cooler 70's to 80's. Took car out for little blast and in pulled fantastic. But noticed idle O2 now reading 13-1. Took it out again a week later. When I started it, idle read 14-1 and started coming down(richer) as car warmed up. On next blast fuel mixtures at above 19lbs boost up to 23lbs read 11.3-1 and computer was adding 5% fuel to get there. I do not have any warm up enrichments programmed in yet. Is it possible 20 degrees of outside temp. could change the mixture that much. And as for idle why did it change so drastically? It is a twin plug motor and I run regular Bosch plugs in bottom and Bosch race plugs in top. I guess it is possible that I fouled out the race plugs and when the engine mixture got better it cleaned off plugs and they started firing. I checked the O2 for accuracy, I checked fuel pressure, Idle vacuum is better than before. Only thing i can think of is plugs,warm up enrichments, or some type of fuel restriction. Any thoughts?
Old 11-07-2014, 04:10 AM
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