CA Emissions Testing: High NO
 

For those of you that have to deal with the enhanced emissions testing in CA, I have a question regarding high NO readings during the 15MPH portion of the test.

Here's the NO numbers:

15MPH
1316 RPM
Max: 772
Ave: 237
Measured: 772

25MPH
1131 RPM
Max: 711
Ave: 199
Measured: 492

I just passed the 15MPH portion of the test.

My question is, would removing the EGR "walls" in the plenum have something to do with this? Perhaps not allowng the intake to draw enough exhaust?

IIRC, the NO levels have been historically high. However, I'd have to go back and see if I still have the readings before and after plenum porting. BTW, my intake consists of an Edelbrock base, SLP runners and ported plenum.

The HC levels are pushing the upper limit too at both road test speeds. I think the converter isn't staying hot enough because of the SLP tri-y headers.

Thanks.

Not CA, but CO.

Not TPI, but carb.

In general, though, high NOx is due to high combustion chamber temps. A common cause is timing too far advanced. Know where yours is?

Just changing the EGR wall shouldn't have affected the effectiveness of the system. Blocked EGR passages is a different matter. Headers shouldn't have affected the cat significantly.

For the record, my before mods stock LG4 and after mods NOx numbers were almost identical. All numbers (HC, CO, NOx) were lower after the mods than they were before.

Timing is set to whatever the underhood sticker specifies; 6*BTDC if I recall.

I do know that the headers did effect the function of the cat somewhat. The tech that performed the emissions test after the headers where installed commented that the cat seemed "weak"; he had to run the car at a relatively high RPM for a long while to get it hot. The tech had previous history with testing the vehicle.

Also, at the time I purchased the headers, SLP offered both a 49-state and a CA version. The only differences between the two was header wrap on the CA version, presumably to retain exhaust heat. At the time, I lived in an exempt county and it didn't seem worth the money to spend the extra $200 for the wrap.

Thanks for the input. I guess I don't need to be concerned until 2007 when testing is again required.