dv013003

I just installed a wideband O2. At idle it bounces around 14.9. At WOT it is at 14.7 ro 14.8. But when I let off the gas after WOT, the reading jumps to 22:1 which I believe means that it is running super lean (the max the gauge can read)? Why is this? How can I fix it? Is it harmful?

Thanks

Apeiron

It would be helpful to know something about the car.

dv013003

Sorry. It is an 89 firebird. 350 tpi. All of the free mods and bolt-ons possible. Timing was set at 10 above. Running 93 octane. I just turned it down to 6 and I'll let you know what effect that had. There is also a slight bounce in the idle (only around 50-100 rpm difference which could be a miss). All maintenance has been kept up on.

Apeiron

Your injectors are shutting off on decelleration to save fuel.

dv013003

Is that normal / safe? Can it be changed?

Also, I changed the timing down to 6. It seems to actually run a little leaner at WOT. It bounces from 14:7 to 15:5 A/F Ratio. And after a WOT run, as I decellerate, it runs 22:4 until it downshifts into second at around 40mph.

Apeiron

Why would you want to change it?

dv013003

I thought that 22:4 is extremely lean in the cylinder, and so could create tremendous heat ??? Don't we want to aim for 14:7 or a little less so that there is extra fuel for cooling or to avoid a lean condition.

I must be missing something--why is it ok to have 22:4 at deceleration, but not acceleration? Also, Is there a way to richen the mixture at WOT without using computer tuning devices?

86LG4Bird

iTrader: (1)

With the injectors shut off, there's no fire, no heat.
It's good. Leave it alone.

Without computer tuning, there's no reliable way to adjust WOT fueling on a closed loop feedback EFI setup like you have.

Apeiron

It's not 22:4 and 14:7, it's 22.4:1 and 14.7:1. Your mixture isn't 22:4 on deceleration, that's only as high as your gauge reads. The mixture is really infinity-to-one, as in there is no fuel in the charge.

RockinGTA89

agreed with 86...without any form of computer chip tuning you can't alter the air/fuel mixture off the ecm which has a specific data table to where the air-fuel ratio is set to, from the factory. Changing the timing will not do anything to change the injector run time or air mixture...

it is normal for vehicles to briefly run lean for periods of time as this won't do any damage when your on a decel... injectors will cut down on pulse width run time to a minimum, unless specified by throttle position is sensed and in relation to other sensors such as map, mass, and/or baro...(which senses air charge, temp, and vacuum in the intake side of the system.)
the O2 only looks at whats coming out of the exhaust and as the ecm reads it, it adjusts the fuel requirements as needed accordingly to the data table that is set in the ecm fuel trim constants...

Viprklr

iTrader: (5)

It's normal.

Damon

It's normal. Happens with carbs, too. There is almost no cylinder pressure on the over-run and almost no combustion going on in the cylinders so there is no harm done. If it was like that under a load you'd be in trouble, but an over-run condition is a special circumstance that doesn't share much in common with more typical engine running conditions.