P38A GEMS 4.6 Reset fuel trims

Guys,
Have just replaced Cats & Rear Silencers plus cleaned the O2 sensors following MOT emissions fail. Will also be doing air filter etc. but wondering about fuel trim reset via Nanocom. Last year the emissions were well inside the limits.

1. It is worth reseting the trims, or just allow the GEMS ECU to adjust automatically ?
2. If I do reset trims, how long does it take the ECU to stabilise ?

Pete

If it failed the emissions, something must have caused it to run rich. When was the oil last changed? When were the plugs last changed? When was the air filter last changed?

You see where this is going?

My own car failed due to mice munching the plug leads, but that was after it laying up on a farm for five years.

Do you have LPG? If yes, then that is always a factor, if not, perhaps it's time for a service and some new plugs & leads.

Was there a lot of soot on the cats or the down pipe from the manifold?

Sometimes an Italian tune up (flat out between the gears to clean the pipes) helps before a test, but usually the sparks & wires and check the temp sensor is working (if it thinks the engine is cold, it will tell the ECU to run rich).

Yes will be doing plugs, etc. but I suspect the CAT's are knackered. Probably does need a good "Italian Tune Up" as well, because I don't do many long trips, and even then it's cruise at 70 down the M3. No LPG. I'm fairly sure the temp sensor is ok, because Nanocom was reporting sensible reading from this one relative to gauge sensor.

As usual I will be checking everything thoroughly, but really just wondered about the trim reset cycle timing ?