I am going to get this car smog tested again. It keeps failing on high NOx ever so sightly. Just replaced the manifold and exhaust gaskets and the catalytic converter.

To further increase my chances of passing, I would like to advance? the timing timing by 2 degress (12 degress +- ok).

Is that correct? Does advancing help NOx or is retarding the timing?

And which way would the 'back of the cam' distributor housing rotate to advance or retard the timing?

The cam turns clockwise with respect to looking at the rear of car (top of cam travels toward driver side)

...so that would mean the distributor housing would need to rotate counter clockwise to advance timing? This would cause the spark to happen 'more before' TDC.

So an advanced timing would be +14 degrees BTDC and a retarded timing would be +10 degrees BTDC. This would be read off the timing scale.

Thanks BB

Rob 91 740 na rex/regina

They check your timing during the smog check! assuming your in california, its part of the test's they run through the process, changing it will make you fail that section.

timing in your model is controlled by the crank sensor on the bellhousing. the distributor has been largely left with distributing spark as the rotor whizzes round.

there is little you can do to modify the timing other than be off a tooth on the t belt at the cam sprocket which will make the car run crappy.

nox is normally an air leak into the exhaust stream problem.

Yes, I am in Cali.

This car is failing ever so slightly for low speed NOx.

I was hoping that a little advance or retard of timing would help.

I assume a + or - on timing would be ok with the check.

So back to my question, which way would rich the fuel mixture. + or -?

...and which way would the distrib housing rotatate to acheive this?

So you say no matter what I do at the housing, the rpm sensor will compensate?

Rob,

If I understand it correctly (someone please correct me if I'm wrong) the adjustment on the distributor is so that you can get the rotor in phase with the contact on the cap so that it does not fire when they are not lined up. So, turning the distributor does not change the timing.

Charley

...to change timing.

It's controlled by the EZK Ignition CU.

The RPM Sensor is the basic input to the ICU as the fixed reference for ICU timing control.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Ill list some reasons of high NOX out of a auto book that I have.
High NOX created when combustion chamber temps become to hot or an excessive lean air-fuel mixture.
Vacuum leak
leaking head gasket
engine carbon loading
egr valve not opening
injector not opening
low fuel pressure
low coolant level
defective cooling fan or fan circut
oxygen sensor grounded or responing to an artificial rich condition.
fuel contaminated with water.

Hope this helps, also if you drop your car off to get it smogged, if you wait leave it running while you sign it in or just get off the highway, its better for it to be up to temp rather than pulling in and shutting it off.