High HC fail during smog (CA but relevant to all emission testing)

[Flash]

88 325i, car runs rich, nox, and co2 numbers are fine. It seems like the numbers are high due to unburnt fuel.



Been working on these for a decade, know the name of every sensor, know how to test, etc...
Every time ive ever smogged a car that failed was due to high nox, and replacing the 30 year old cat always fixed the issue. Could it be the cat? Replaced AFM with a known good, o2 sensor changes voltage and within spec, no vacuum leaks, have not changed the FPR or injectors and dont suspect them. Spark plugs look fine, lots of electrode left, no carbon, normal wear. Wires have normal resistance.


Could it just be the cat? I can replace that, i just find it hard to believe it is. Low speed (15 MPH test) failed by an additional 30% higher than allowed, high speed (25 MPH test) passed barely, everything else is great and car runs great except it smells rich as hell.



Any input is appreciated.

[Cayoncrusier93]

Rotor and distributor cap been replaced recently?

[Flash]

Rotor and distributor cap been replaced recently?

I have not taken that off yet, was going to replace the fan clutch and radiator on the car in question but will inspect it.

[McGyver]

This thread may be useful for you:

https://www.r3vlimited.com/board/showthread.php?t=423291

Also, try typing your numbers into a lambda calculator. It will help to identify how the engine is running and whether the cat is working or not:

http://www.smogstats.com/lambda_cat.aspx

[TheRob]

How do the NOX emissions look? Also, post a picture of the smog report, its helps to figure out whats going on. Definitely do what McGyver said and run lambda to see if you're in fuel control or not. If the numbers skew one way or another to far past 14.7:1 you're cat won't work correctly so even if you did replace the cat it would probably still fail. You could have a failing O2 but that will usually affect NOX emissions as well. A cat failing and only allowing HC numbers to go up is a bit strange, you could have another problem going on here.

[reelizmpro]

You should post the results so we can see the numbers in relation to each other. High HC's tend to destroy cats which leads to high NOx. In this case, only the HC's are high which tells me it's rich (or unburned fuel) but the cat is still good. There must be a reason for the high HC's. Does it have a chip? You should verify the FPR doesn't have a ruptured diaphragm leaking fuel into the intake and that the injectors aren't leaking and operating like they are supposed to. It wouldn't be too hard to check on an M20. Test for spark, make sure it's a nice healthy spark at all of the plugs. Go ahead and replace them while you're at it with some fresh coppers. Are the wires aftermarket? if so, are they designed for bare plugs or plugs with acorn nut terminals? Are you sure there aren't any vacuum leaks? check the purge valve hose? Brake booster hoses/fittings, Idle control valve fitting? Is the blue coolant temp sensor within spec?