i have a 90 crx si with a d16z6 swap. im running obd0 right now with the stock crx ecu, stock crx dist, and no vtec. i failed my emissions test for high NOx. the state standard is 2.5 gpm, and i scored 2.8374 gpm. since i only have one free retest, im trying to go over everything before i go back. the o2 sensor was changed only 6 months ago and the cat converter is 2 years old.

i checked my ignition timing, and it was turned too far back towards the firewall (i think retarded). i fixed the timing to stock. the last thing i want to check is the EGR valve, which my mechanic friend told me to check. i was looking in the honda service manual, and it seems that the Si didnt come with one? only the std. and the HF? so what should i be looking over if this is correct?

any advice, comments, suggestions, would be appreciated...thanks

edit: im using a z6 intake manifold

 

did the d16z6 come with a EGR valve? will this be a problem when i switch to obd1? also, does anyone have a pic of an EGR valve?

 

The D16Z6 did not come with an EGR valve.

 

could the retarded timing have caused the high NOx readings?

 

NOx is from the internal temps being too high.

It's a common problem with a bad O2 sensor.
O2 won't throw a code unless it's completely dead.
When the get old they get 'lazy' and react slow and you don't get a code.
This will sometimes cause the engine to run lean and thus high NoX.

If the timing is advanced internal temps go up and so does NoX.

Corbon build-up on the piston tops can retain heat and make the internal temps go up as well.

How are your other numbers on the smog test?
If some of the other test results are on the high side you may be due for a cat.

 

Hydrocarbons Carbon Monoxide Carbon Dioxide
State Standard 1.4 gpm 30 gpm N/A
My Reading 1.2548 gpm 5.4107 gpm 258.6311 gpm

i passed everything else, and im really not trying to buy another o2 sensor..this one isnt that old. so actually now that i had to advance my timing to get it normal, the NOx reading will be higher?

thanks

 

Yeah, EGR was only on the HF and auto's.

Rotating the distributor towards the firewall advances, towards the front of the car retards. So you were advanced and that didn't help NOx. So if you set it back to stock you were retarding from what you had and it should help. The spec. actually allows +/-2 degrees, so you can retard it 2 more degrees for added measure before you go back.

Like was mentioned, NOx forms when combustion chamber temps are +2500 degrees. So if you're still high, you can try the highest pump octane and even a step colder plug should help bring the temp down.

 

thank you!