AFR reading between shifts

[iamchappy]

My LC-1 appears to be working correctly up until i shift, then it pegs at 18 for a second or two before returning to normal.
Could this be caused by flames shooting out my tail pipe . My sensor is located about 22" downstream of the turbo and about 16" from the end of the tail pipe.

I dont know that flames are but I could hook up the Go-Pro to check and see.....

[Tippy]

Raw fuel will actually read as no fuel, so yes, that may be it.

I don't know if CIS has a fuel shutoff as that can be it too.

[proffighter]

EFI or CIS?

However, here is what happens when I shift:

[Ken911]

Sometimes when it backfires and pops during decel and between shifts when the gas ignites and explodes out of the tail pipe air rushes in backwards which will also give you a signal like that. Mine has a dual out and i have to block one of the pipes to even get a steady reading during idle.

[mark houghton]

Originally Posted by Ken911

Sometimes when it backfires and pops during decel and between shifts when the gas ignites and explodes out of the tail pipe air rushes in backwards which will also give you a signal like that. Mine has a dual out and i have to block one of the pipes to even get a steady reading during idle.

I believe you've hit on it. I laid awake last night trying to puzzle this out.

Remember that these O2 sensors for the AFR gauges are reading the amount of oxygen remaining after combustion. If you're reading high AFR's, that means that there is excess un-consumed O2 still available (in other words, not enough fuel to consume all the available O2). One would think that in the case of excess fuel in the exhaust system (i.e, muffler) there won't be enough O2 present to completely burn all the fuel...i.e, all the O2 has been consumed trying to combust all that extra fuel...which means a low AFR reading 'cause there aint no oxygen remaining but just a bunch of raw fuel drooling out the exhaust pipe after it's done blowing flames. So the only way for a high AFR would be if fresh air were to be re-introduced between shifts.

My AFR sensor is located about 11" inside of the exhaust tip, and yet I don't see the AFR's peak lean between shifts (actually, just the opposite as the throttle plate closes and restricts any more air from entering the combustion chambers). But then I'm not running pig rich on boost either and as far as I know I'm not shooting flames. I usually look straight ahead when seriously 'getting it on', not really caring what's going on behind the car.

[Ken911]

mine spikes every time i shift. the sensor is located about 6 inches from the end of one of the tail pipes. right after the emptybox/muffler.

[cliyde]

Normal behavior on my 3.2T when the throttle plate closes - no fuel , no combustion, only O2 flowing through. Also, fuel injectors will turn off until the rpms return below 1000 RPM.

Originally Posted by iamchappy

My LC-1 appears to be working correctly up until i shift, then it pegs at 18 for a second or two before returning to normal.
Could this be caused by flames shooting out my tail pipe . My sensor is located about 22" downstream of the turbo and about 16" from the end of the tail pipe.

I dont know that flames are but I could hook up the Go-Pro to check and see.....

[gavinc69]

Mine also does the same thing, AFR jumps about showing 14+ to 15+ on down shifts as its popping.

[mreid]

That's normal. If EFI, the ecu will also shut off fuel as it reads a high vacuum with no load.