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Unread 06-26-2013, 04:57 PM   #1
biggreen
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1995 ZJ 
 
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5.2 failed smog any ideas?

my 5.2 failed smog last weekend due to a very high hydrocarbon at idle. At higher rpm it passed with flying colors but at idle it was more than 4 times the max amount allowed. A few people told me to replace the cat so i went ahead and did that and haven't retested it yet. I wanted a couple more opinions first.

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Unread 06-26-2013, 05:00 PM   #2
tucsonzj
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mine did that, check all your plugs, iac, do a fresh oil change right before you take it in to get tested. Use some junk out or whatever it's called fuel system cleaner the tank before you get it re-tested.
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Unread 06-26-2013, 05:13 PM   #3
biggreen
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I just replaced the iac but I will definitely check the plugs as well as run some fuel cleaner through it and do my oil change since its due for it anyway
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Unread 06-26-2013, 08:44 PM   #4
Candymancan
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If you replaced the cat.. go check it again.. they should do it for free the second time.. That's how they did it around here when you fail emissions
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Unread 06-27-2013, 01:03 AM   #5
kachink
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Hydrocarbon is unburned gas. I would suspect maybe the O2 sensor, or an exhaust leak upstream of the O2 sensor that is sucking air in and fooling the computer into thinking it's running leaner than it really is. Are there any codes stored?
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Unread 06-27-2013, 08:04 AM   #6
exmilitary
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If the truck has it you might want to check egr valve. If it is defective it will give hc and no2 readings.
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Unread 06-27-2013, 10:24 AM   #7
just_urd
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Replace the cat, save the old one, have them do a bolt on set up, drive straight from there and have it smogged. Assuming it'll pass, put the old one back on, and save the new one for a spare when it really needs to be replaced... Gotta love California emissions.
If it runs good as is, don't change anything else, unless it's absolutely needed...
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Unread 06-27-2013, 11:07 AM   #8
tucsonzj
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Quote:
Originally Posted by just_urd View Post
Replace the cat, save the old one, have them do a bolt on set up, drive straight from there and have it smogged. Assuming it'll pass, put the old one back on, and save the new one for a spare when it really needs to be replaced... Gotta love California emissions.
If it runs good as is, don't change anything else, unless it's absolutely needed...
He already replaced the cat
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Unread 06-27-2013, 11:11 AM   #9
just_urd
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Quote:
Originally Posted by tucsonzj

He already replaced the cat
Yeah, I've been having this problem of over reading some posts. I need to work on it... Especially if I'm gonna drop my two cents.
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Unread 06-27-2013, 11:34 AM   #10
zjosh93
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Simplest thing you can do about hydrocarbons at idle is to make sure the engine is hot when they smog it. Drive up and down the highway and then go straight to the emission testing center.
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Unread 06-27-2013, 01:21 PM   #11
biggreen
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Thanks for all the advice. I will be taking it to get smogged again probably on Monday after I get back in town. Hope for the best!
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