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why is it running lean?

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Old 04-20-2006, 12:35 AM
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Ah ok, I wouldn't really think bullets would skew the AFR reading that bad but a car I tuned awhile back had a semi-open Borla that threw the AFR off, and I have back to back dyno pulls on my car.. one in the cutout and the other in the tailpipe (after the muffler) that showed a whole point difference (leaner out the back) while my wideband in the Y pipe stayed exactly the same on both pulls.

I was asking because it doesn't make sense for the car to be that lean on the stock tune with no more mods than you have. Can you check the injector duty cycle? Is the MAF stock?
Old 04-20-2006, 04:29 PM
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I thought it may be from an exhaust leak also but the guys at the dyno said that if the car is at WOT then it wouldn't be able to pull in air because the engine would be pushing it out too fast. I think it is leaking from where the headers meet the xpipe. Think this could be the problem?

I am going to take it back and they are going to hook it up to a computer and monitor what is going on. I won't be able to make it back till the 6th though. I already swapped out MAFs on the dyno with one that for sure worked and no changes in the a/f.

We also reflashed the computer just incase there was any programing on the computer since I bought it used and that didn't change anything either.
Old 04-20-2006, 09:39 PM
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Originally Posted by Radcat
I thought it may be from an exhaust leak also but the guys at the dyno said that if the car is at WOT then it wouldn't be able to pull in air because the engine would be pushing it out too fast. I think it is leaking from where the headers meet the xpipe. Think this could be the problem?
With the higher velocity of the exhaust it is going to create more vacuum to pull in air from the leak. Are you in stillwater MN? If so where did you take your car?
Old 04-20-2006, 10:25 PM
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Nope I'm in Oklahoma. So the high reading is probably from the exhaust leak?
Old 06-18-2011, 12:08 PM
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I need some help guys I have an ls1 heads cam supercharged it's running 13.6 is that to lean ?????
Old 06-18-2011, 03:27 PM
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Originally Posted by 383ss

also, 02 sensors have absolultely no effect on WOT a/f.
if you have a bad O2 sensor it will throw your fuel trims off. Those incorrect/ bad fuel trims will lock in at WOT, throwing your a/f ratio off during WOT.
Old 06-18-2011, 04:03 PM
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also, I'd like to add that a dirty mass air flow sensor will cause incorrect a/f ratios.




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