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Thread: One bank shows a point lower AFR than other?

  1. #1

    Default One bank shows a point lower AFR than other?

    So I took my car to the chassis dyno a week ago, and the WBO2 sensor on the dyno read lean coming off the driver side. The Holley NTK on the passenger side said it was correct. We tuned the car to the dyno sensor on the driver side, and the car responded well with the closed loop off, but on the ECU with the sensor on the passenger side said it was rich. Took car home thought something was wrong with the NTK sensor on the ECU possibly. So I moved it to the driver side and put a LM1 wideband on the passenger side. The driver side still read leaner by 1 whole point or better and seems to have a bit more fluctuation, which tells me the Holley NTK sensor & ECU is working correctly. Can't find any exhaust leak, intake is fine, plugs from one side of engine to other look almost identical. Going back to the dyno tomorrow to finish the tune, and going to tune off the side reading lean driver side. Question, is there anything that can cause this? I'm running the injectors Paired could that be a problem? Should I go Bank-To-Bank? Sequential with no cam signal? Or am I missing something. The engine is a ProCharged 388, solid roller, 90 mm throttle body. I would rather play it safe than go lean & hurt it, but it seams weird and would like to figure it out.

  2. #2
    Join Date
    Nov 2013
    Chicago IL


    When one side is much leaner than the other, either you have a bad WBO2 sensor, or an exhaust leak.
    Easiest thing to do is to have somebody smoke the exhaust to check for leaks. Then if you find a leak, weld it up.

    If there are no leaks, start looking at replacing the WBO2 sensor. Buy one new one & install it. If the side you install it reads differently than before, that's the correct one to replace. If it doesn't change, swap it with the other one, and check it.
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

  3. #3
    Join Date
    Dec 2009

    Default (Read "Potential Causes of L & R Bank AFR Differences")
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, 36-1 crank trigger, 1x cam sync, 200A 3G alternator, Optima Red battery, R134a A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM converter, B&M Hammer shifter, Stifflers trans crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

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