On my mission to breathe new life into a neglected and abused RX-8, I've found a vacuum leak in the intake accordion tube that is causing high fuel trims.

Based on my admittedly limited understanding of the inner workings of the catalytic converter, I think the excess unburnt fuel will probably clog the cat, if it hasn't already. My question is this, should I avoid running the engine until I've replaced the accordion tube, or is it not likely to make a difference?

Thanks.

--
Joshua Colson

 

I'll try and make this easy to understand

The MAF measures air that flows past it. The computer adds fuel based on that amount of air.

When the car runs that mixture is burnt and the O2 sensor measures what it expects for an air fuel ratio

When the car is in "closed loop" mode it uses the AFR reading from the O2 sensor and adds or subtracts fuel to get what it is looking for as a result in the O2 sensor.

If the fuel adjustment is short term....IE only happens as a transient it will add fuel via the short term fuel trim. If it always happens the same places the ECU learns it needs more fuel there and will add a long term fuel trim that the ECU remembers

If you have a vac leak....there is air that is not being measured by the MAF...so that makes the ECU inject less fuel than needed..and it will add fuel via a ST and LT fuel trim to compensate for the leak.

Your CAT will see the AFR that is derived from a correct mixture after the adjustments so it won't hurt the CAT

Usually the CAT is damaged by fuel that isn't burnt due to ignition misfires due to crappy ignition components

 

This should be added to the new owners thread. it is something everyone should have an understanding of.

 

Thank you, dannobre! That was a very clear explanation. That is why once I've fixed the vacuum leak, I need to reset the ECU so that it forgets any long-term fuel trims it has learned, correct?

 

That's the easiest way.. although the computer should correct the LTFT over time when it learns that there is too much fuel in those spots.

If you reset the computer it will start at the baseline fuel setting and learn from there

The reset will likely make the idle a bit flakey for a few drive cycles but will straighten up after that