Failed smog today w/ high CO and HC levels at idle. Readings are below:

Idle:
CO2%: 14.10
O2%: 1.20
HC: 123 (Max is 120)
CO%: 1.36 (Max is 1.00)

2500 RPM:
CO2%: 14.80
O2%: 1.20
HC: 15 (Max is 140)
CO%: .08 (Max is 1.00)


Any help? It appears to be running rich and I will check the O2 sensor tomorrow, but are there any other ideas?

 

I would put in a new set of spark plugs unless they are very new. O2 sensor would be a good guess if it is the original. Take a peek at the air filter also.

 

What gear did he use for the dyno runs? Ditto on the plugs, and air filter, but I think a bad O2 sensor would have you showing worse than that. You are close to passing; just make sure your cat is scorching hot from a high speed freeway run and don't let it cool down sitting in the parking lot before the test. There's always xylene for the emissions impaired.

 

High CO's usually represent bad cats or bad O2 sensor.

 

Setting the idle speed up a bit would help although I'm not sure it's legal in CA- you may have to disable the idle control cicruit.

I'd take the car with the repair manual to an independent service station. For a minimal charge, they'll adjust the idle mixture on their machine. The key is too make it easy for them. Highlight the procedure in the manual and circle the adjusting screw. Explain this is all you want done. If they ask you to sign a waiver or won't let you watch, try another station. There's got to be one decent grease monkey left in the state. If not, you have a great reason for a road trip to Nevada.

Odds are this is a tuning, injetor, or oil control issue. At idle, chamber mixing is poor and intake vacuum is high. An injector leak too small to effect driving could be significant at idle. Idle vacuum tests weak intake valve seals, rings, and turbo bearings where applicable. Increasing idle speed increases the overall need for fuel and may give the computer the tuning room it needs to compensate.

The O2 number is used as a surrogate for NOx and to catch blatant cheaters. It will go up if your car is lean or if you are diluting your exhaust with a leaf blower (aka electric supercharger) Since your idle O2 is OK, I don't think your HC problem is from a vacuum leak/lean misfire. High CO supports a generally rich mixture as the root cause.

If your car has exhaust gas recirculation- my 86 does not but I don't know much about newer versions- check its function. It should be disabled at idle. EGR at idle overcools and dilutes the cylinder charge. It can cause a misfire similar to lean-limit without the tell-tale high O2 levels. Note that this only applies to older cars. New cars (OBD and later?) use EGR to boost fuel economy and as a general tuning aid.

Bill

 

You must live outside the city to not have to dyno your car for smog. The idle is the only thing failed so your cat is working very well when nice and hot with the car running at 2500 rpm. A good warm up of your cat before the test will take care of your problems unless someone mistaken the idle mixture screw for the idle speed control and screwed around with it. The ONLY thing I would adjust if I had to is the idle mixture and everything else is working well as indicated by your 2500 rpm readings. I am willing to bet it will pass just by having the cat warm before the idle test.

 

Thanks all. Lots of good info. The shop was suggesting cat, but at speed everything is good, so I wasn't sold on that.

I'll try driving around at high speeds before the next test. I did some in town driving before taking it and letting it sit prior to the last test. Plugs and air filter couldn't hurt either.

 

Ok, here goes:

Your HC problem is caused ye the CO problem, HC is an idicator of misfire, obviously at idle you have high CO (rich) causing a misfire (high HC) and then as RPM increses your numbers improve, this implies that you have too much fuel at idle, this could be: Idle mixture too rich, Leaky injector, or high fuel pressure.

I agree with everything bill.e1 said except the part about EGR
EGR doesnt cool the intake charge, it replaces air with an inert gas, so you get less of an explosion, causing cyl temps to drop below 2500 deg. (anything above 2500 causes NOx). And the misfire it causes is called a density misfire. And it still will increase 02 levels, any misfire will increase 02 levels.

HTH...
Mark

 

Mark,
Sorry, poor choice of words. The temp is lower but, as Mark states, it is not due to cooling.
Bill

 

Add a bottle of Techron to your tank and get your cat hot.

 

I'm going through the same problem. Funny thing is I passed last year. The only thing new on the car is a Burch exhaust header. I had a straight pipe, but went ahead and put on a magnaflow cat, stock after the cat though. I've had some starting issues though and have had to use some starting fluid in the morning to get it going. It was really hot when I tested the car. CO max in CA is 0.58@15mph i stestd at 1.05 and 0.44@25mph I tested at 1.42...everything else passed. The guys says it may be the o2 sensor, but I replaced that 2 years ago...would running a straight pipe with the O2 sensor mess up my fuel reading?

 

Don't forget all the diaphragms in the fuel system(i.e. fuel pressure regulator). If one of them is cracked, it will leak fuel thru the vacuum line into the manifold. Probably effect the idle the most, I would imagine. For the $60, I would replace the fpr.

 

there's also an adjustor on the AFM for idle AFR. at least the early ones.

 

CA smog tech here.. Your oxygen levels are slightly high... is there a vaccumme leak?