I just went for a re-test on my 1994 pickup. To make a long story short...It failed on hydrocarbons. Max allowable is 60 and my truck registered 64.

Prior to this test, my truck failed on timing and CO. That problem turned out to be the TPS, which I replaced the day before the most recent smog test. So while replacing the TPS I thought it would be a good idea to clean all the gunk out of the throttle body. I noticed the gunk was into the intake manifold, and I tried to clean some of that out too. So here's my question:

Could the gunk I dislodged from the intake and throttle body cleaning be the culprit for the elevated hydrocarbons? And what would be the diagnostic workflow if this is your truck?

Thanks Todd

 

Well, if you lived in the SF Bay Area, max allowable HC is 64ppm at 15mph, 40ppm at 25mph.

The good news is that your CO2, O2, CO and NO are all very good. The bad news is that this does point to a tired Catalytic converter.

But first, read this: http://www.cygnusx1.net/Media/Supra/...taTech/h56.pdf That article (which is slanted toward vehicles newer than ours) concludes your most likely problem is misfire. Does it run a little rough at 25mph?

 

It's running smooth at 25 mph and acceleration, but is a little rough at idle and causes the stick shift to bounce around a little. One other thing I've noticed is that the sound of the motor changes as I decelerate. I'm not sure if " throaty" is the correct technical term, but that's what it sounds like. I'll try to capture it on video.

Thanks for the reply

 

How old is the converter? The CO looks like it's way above average this usually means its running rich or you have a tired converter.

 

Alright. I finally got the truck smogged and it barely passed! I did an oil change, added some fuel treatment, and did a quick tune up.

Come to find my truck has the original catalytic converter. That's over 424,000 miles on it. That's pretty cool in my book.

Thanks everyone for the responses and advice to this post.

Todd