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anyone have any info regarding emission vs timing ?

i have some problem with completing the smog test.

co2500 raised idle

sometimes my hc goes skyhigh but lamda still around 1

Hi Ne_Mesis,

This diagram may be of assistance to your question.

With the HC values going up, do you have a leaking injector? or and occasional miss that may be loading unburnt fuel into the exhaust. Sometimes this can also be caused by the action of the engine breather system and the PCV, with excessive blow by going through the engine.

Attached Files

yepp ive taken all that in consideration.

my pcv and breather is unplugged during the test

leaking injector should in my mind result in an dip in lambda aswell.

but when i rolled back and plugged in an old ecu then it was all fine... but the exhaust was 200C diff on the two setups

the engine is newly built and leakdowntested. my idea was also oil, from pcv vent or the valve seals or turbo.

but the temp made me think if it was related to ignition somehow


Ignition timing that is too far advanced will result in high NOX. Ignition timing that is too far retarded may result in high HC or CO.

Perhaps try a little more ignition advance in the low-load areas just above idle?

Can you look at the timing map for the old ECU, or use a timing light to determine what timing is being used to pass the test?

Also make sure that the timing that is being requested is the same that is being delivered, it may be that the new ECU is a few degrees off in it's Reference Offset value.

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