Running lean on overrun

[Jhonno]

Cerb keeps pinging afra and afrb on overrun.. On throttle it's fine, around 0 or -ve adaptives.. But when you back off the adaptives spike and it throws the fault (not logged)..

Any ideas? Running too lean on idle? I am planning to get the injectors returned/cleaned anyway.

[jamieduff1981]

Vacuum leak on throttle body thermal barriers?

[fatjon]

It's normal to run lean on the overrun. Most cars get down into the 17:1 to 20:1 on overrun. No point in peeing fuel in when no power is needed and the manifold is in high vacuum and the throttle plates are closed or pretty much so.

[Jhonno]

fatjon said:

It's normal to run lean on the overrun. Most cars get down into the 17:1 to 20:1 on overrun. No point in peeing fuel in when no power is needed and the manifold is in high vacuum and the throttle plates are closed or pretty much so.

Enough so to throw afr faults though?

[fatjon]

As in MIL lights and beeps or as in ECU logs a transient lean condition. Not too familiar with the MBE diagnostics as mine has been on an Emerald for years. Mine dips to fresh air (fuel cut) on a hard overrun and down into the 17.5 to 18.5:1 on a moderate overrun.

[Jhonno]

It doesn't log it, it just pings an afr fault in the short term memory of the ecu, rather than the logged faults

[jamieduff1981]

Mine has never lit the MIL even with failed lambdas and terrible misfiring.

[fatjon]

I wouldn't worry about it then. It's probably just the MBE firmware that logs the lean condition even when it's an expected lean condition, hence no MIL or beeper.

[fatjon]

jamieduff1981 said:

Mine has never lit the MIL even with failed lambdas and terrible misfiring.

On the MBE mine lit up and beeped when I connected the lambda wires to the wrong banks but that was about the only thing that did it and it stunk of fuel and ran very, very badly.