I have some qeustion about emission and tuning.

1: Can to little or to much timing have a negative impact on the emission results? Im up for “sniffer” test here in Sweden, and just whant to be one step ahead.
I heard that Retard the timing a few degrees will help to drop the emissions a little?
In Sweden we only test idle, and “raised idle” ( around 2000rpm ).

2: On my engine I changed the ECM proportional gain, to get rid of some low rpm “surge”. Can this also have a negative effect on my emission results? Should I change back those settings to “stock” before the sniffer test?

3: Will diffrent heat range on plugs, make any impact on emission?

Any tips to improve the odds of passing an emissions test would be Aprichiated.

Thanks

 

ignition timing does have an effect on emissions.
too much advance and NOx goes thru the roof.
too much also raises HC and CO.
not enough timing and HC and sometimes CO goes up.
when we had the 2 speed idle test here, 4~5 degrees of timing pulled could make a car pass that otherwise failed. pulling much more than 5 degrees would cause HC to go up.

the heat range of the plugs can affect emissions. if the plugs are too hot, you can get preignition, which will cause NOx to spike.
too cold and they may foul and cause a misfire, HC will spike.
misfire can cause a false lean condition and CO starts going up.

you want the idle as stable as possible.
if its surging, the ECM is adding or removing fuel, advancing or retarding timing.

before you go in for testing, check over everything to be sure its all working properly. EGR, fresh oil and filter, clean air filter, no vacuum leaks and so on.
don't forget about the AIR injection system if you have it, if its leaking fresh air into the manifolds when it shouldn't, the O2 sensor will think the motor is running lean and add fuel.
if your O2 sensor is old, a new one shouldn't hurt.