Failed Emission Test - High HC

[Tafkah]

Hi guys,

My 89 Vanagon MT failed the Utah state emissions test because of high hydrocarbon at idle.

Here's my test results:

At 900 rpm: HC - 391 PPM, CO - 0.63%, CO2 - 12%, O2 - 4%
At 2500 rpm: HC - 123 PPM, CO - 0.70%, CO2 - 14%, O2 - 4%

The test was not done on a dynamometer.

Just before the test, I changed plugs, plug wires, distributor cap & rotor, checked timing, new O2 sensor, changed oil and filled up with 88 octane gas. There are no apparent vacuum leaks. I also made sure the engine and cat were very hot before the test.

The cat is one of the $100 units from bus depot, installed 4 years and 36,000 miles ago.

The van runs great and gets about 19 mpg.

After the test, I found two small exhaust leaks where the manifolds bolt to the engine. Would that be enough to cause high HC? What's are the next most likely causes?

[Petervw]

[Love My Westy]

I failed Utah Emissions with high HC last fall. It turned out to be a loose connection from the 02 sensor.

[chimivee]

Ray - Did you ever get this resolved?

My van just failed CA emissions for the same reason: High HC at idle (fine at 2500 RPM). Have about 6k miles on basic tune-up items, O2 sensor and temp sensor. 2 years / 10k miles on cat. I realized after the fact that I was due for an oil change.

Ideas?

Thanks.
_________________
-James
86 Syncro Westy, etc

[bigsteve141]

Has anyone had any luck with this? I am running into the same problem. Cat, o2 sensor, all basic tuneup items rreplaced within 10k.

All of the emissions checks passed fine except HC at idle, which was 634ppm instead of 400ppm max.

I have been told it is possible lean misfire or a vacuum leak, but I don't fully understand those scenarios yet.

[funagon]

[Themasterof42]

I'm in the smog boat as well. Last weekend I took it to the station but my HC's were too high. It looks like the problem was the catalytic converter. The technician hit it with an IR temp gun. Supposedly it should read 100 degrees difference between the inlet and outlet temp. Mine was depleted and thus I had problems even though the screen inside the cat looked good visually. I think it was original to the van so no huge loss. We'll see on Thursday if it's fixed for sure with a new Cat. Might be worth hitting your catalytic converter with an IR temp gun as well if you have one available. Certain running problems can foul even a new catalytic converter pretty quickly I've heard.

[silversync]

Do a compression test and leakdown test before guessing at too many parts to throw at the problem.

A burnt/weak/leaky exhaust valve can cause high HC at idle (which goes away at higher RPMs).
_________________
Roland: '89 Syncro, '02 911 C4S, '10 Audi A4 Avant

[Jteerlink]

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