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Old 05-14-2009, 09:29 AM   #1
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Default Tuning Vs. Leaky Rings / Valves

So as I mentioned before in a previous thread, I had to do a compression test followed by a leakdown test. These tests proved that I need to get my head redone, cause I had air come out the throttle body and the exhaust during the leakdown test.
I have datalogged countless hours and VE analyzed so many times that I finally found a .msq that I will just have to deal with.
My question is this:
If you have mechanical flaws like leaky valves and maybe rings, would this make your AFR's jump around a lot? Mine do, and it also seems like it misfires, which I think is because of the drastic change in AFR's all the time. I also get resets, at least 1 everytime I do a datalog. I don't mean it jumps around when I am only on the gas and accelerating, but it does it at cruise while maintaining a constant RPM and Vacuum.
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Old 05-14-2009, 06:19 PM   #2
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Forgot to mention, in boost the AFR's stay smooth as silk, and maintain their intended set point...
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Old 05-14-2009, 07:51 PM   #3
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Every misfire puts a pulse of oxygen into the exhaust stream. An O2 sensor NB or WB will record a slight blip as that goes past the sensor. The amount it will affect AFR will be slight same goes for the fuel trim.

HTH

Ron
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Old 05-14-2009, 11:32 PM   #4
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I'd think if you have leaky valves, then they're always leaking a bit, and the amount of the leak isn't varying so much that it's the sole cause of your AFRs fluctuating. Though I suppose it is plausible that as the valve stem spins around and the valve to valve seat interface revolves that the leak could vary in magnitude. FWIW, my engine is in tip-top shape and it's been my experience that AFRs can fluctuate more at part throttle (steady cruise) but stay pretty steady at WOT. So your bad valves may or may not be involved at all.

Another cause of bouncy AFRs could be if you use a different AFR table while tuning in MLV than the table MS references for EGO correction, or the VEs are poorly tuned, or your EGO steps are really big. To see if EGO is involved, just turn it off and see what happens.
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Old 05-19-2009, 07:51 PM   #5
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I have EGO authority set to 20, how much is too much? It seems that if I datalog and then VE analyze it, the changes that are made are only like 1 or 2 points per cell. So that being said, I am assuming that my fuel VE table is correct as per my AFR targets...this is why I think it's a mechanical issue. I just want to make the MS work harder to correct it so I can enjoy driving my car the rest of the summer, cause there's no way I'm tearin down the engine when it's this nice out.
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