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Thread: AFR at Idle

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    TheEngineer's Avatar
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    AFR at Idle

    I'm trying to figure out if my AFR gauge and/or 02 sensor are working correctly...At 58 PSI, my AFR gauge shows 11.7 upon initial startup, and then gradually climbs above 13 while the ski sits at idle. How much variance (up/down) should I expect to see while the ski is sitting at idle? Also, I've read in some other posts, do the 02 sensors go bad when unpowered and left in the exhaust manifold?


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    imp0ster's Avatar
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    Are you in the water looking at this. On the trailer is useless. 02 sensors go bad period. Un-powered has nothing to do with it unless it's sitting in complete humidity and rusts or corrodes.

    when it's warm at idle I shoot for 14 to 14.2.

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    TheEngineer's Avatar
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    Quote Originally Posted by imp0ster View Post
    Are you in the water looking at this. On the trailer is useless. 02 sensors go bad period. Un-powered has nothing to do with it unless it's sitting in complete humidity and rusts or corrodes.

    when it's warm at idle I shoot for 14 to 14.2.
    Yeah, this was on the trailer. I'll water test it this afternoon. I was getting some AFR readings last Friday that didn't make sense, so I'm afraid the sensor is going back (it's barely been used though), or perhaps there was a pressure problem with my fuel line.

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    shrabber's Avatar
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    don't look at it on start up either your always gonna be initially rich on cold start on cold motor. I idle 13.5 ish everyone idle can vary some whats important is wot pulls for rec riders being in a safe afr zone. As You get along you clean everything in between

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    TheEngineer's Avatar
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    Alright, so I know tuning based on the pressure gauge alone is not ideal. But, given the mods I have listed, running 93 Octane, in 85 degree temps, what PSI would one expect to achieve 12.0 AFR at WOT using an 8650 48 169 36 36 VTech Tune?

  7. #6
    PSI in the intake? 8600 RPM on the stock blower should get you about about 185 KPA or about 12.5 PSI.

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    These ski fuel pressure drops and we just installed riva fuel regulato on two rxtx and an AF guage just to check and adjust, And we need to adjust the fuel pressure to 62 pound here in the north east. weather getting a little bit colder. You should install one of these with a AF guage and see what your getting and adjust to get to read 12.4 to 12.6, thats what we are running.We are running the v tech 8500 tune.

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    Quote Originally Posted by whittlebeast View Post
    PSI in the intake? 8600 RPM on the stock blower should get you about about 185 KPA or about 12.5 PSI.
    Sorry, I meant what fuel pressure PSI would be required (roughly). I'm just trying to gauge whether or not my 02 sensor is really going bad or not. I had my fuel pressure regulator set at a much higher than normal PSI and was still not seeing low 12's at WOT. I did smell a bit of gas in the ski, but wasn't sure if that was from a small spill during fill-up, or if I might have a slight pressure leak somewhere in the fuel system.

  10. #9
    The rule of thumb for fuel pressure is 44 to 59 PSI higher than max pressure that is in.the intake. So about 51 + 12 = about 63 psi when running fixed pressure.

    The easy way to verify if your wideband is getting a reasonable AFR is to toss it about 6" up the exhaust of any fairly new car that is idling and warmed up. You better get real close 14.7 or something is messed up.

    Andy

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    imp0ster's Avatar
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    45psi+ with no reference line and bosch injectors. crappier injectors I'd say 50+

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