Won't pass smog. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

74project · 03-01-2010, 11:57 PM

79 chevy won't pass smog. It's been sitting for two years. I changed plugs gas oil and it runs better than ever. It's never not passed but now it's a problem. Any ideas on where to start?

**bwood** · 03-02-2010, 12:18 AM

Not sure if I can help, but it would help to know what it actually failed on. The term "Smog" is kind of generic as they look for specific things and it only takes one of them out of range to fail. Did they give you a printout or readout showing why you failed.

gchemist · 03-02-2010, 12:53 AM

Yea, more info is needed.
Was the cat hot? Were you using the highest octane fuel you could buy? If the truck was parked for two years, you need to run it. Carbon buildup on the valves and exhaust pipe will hurt readings. Was the failure at low RPM, idle or high RPM? What emission equipment is on it?

74project · 03-02-2010, 01:03 AM

Engine was driven all morning on the highway. I did not put high octane in.

74project · 03-02-2010, 01:04 AM

Failed on idle and high speed co output.

74project · 03-02-2010, 01:08 AM

I was going to fill her up with some higher grade fuel what do you sugg? To help clean out the bad stuff

gchemist · 03-02-2010, 01:52 AM

First, run a can of Sea Foam through it. You can buy it at any parts stores.
What is your timing? Can you post the numbers between passing and failing? Is there a big gap? Do you know how to adjust a carb? You could run it a little lean to pass.

Read this on using a vacuum gauge: http://www.centuryperformance.com/tu...e-spg-148.html

73chevyman · 03-02-2010, 11:26 PM

if it where me 1 i would change cap rotor. 2 change spark plugs and the wires. 3 new pcv valve. 4 change the oil. 5 set the ildle to 1500 rpms and drip water in the carb so that all the carbon blows out the pipe redneck cleaning. 6 put 93 oct in with a bottle of octain boost and run the piss out of it till it runs out of gas fill it back up and go streight to the smog test it will pass with flying colors hehehehe.. what i've always done never had a problem

MacAttack · 03-03-2010, 12:40 PM

Had a straight-six Nova with the same issue and all of the items already posted are dead-on, and the only thing I'd add is to use Valvoline racing oil - heaviest grade you can find. That's what I did and squeaked by.

Well, that and the 50-dollar bill I slipped the guy.

(oh wait - did I say that out-loud?

Mac.

73chevyman · 03-03-2010, 05:26 PM

Quote:

Originally Posted by MacAttack

Had a straight-six Nova with the same issue and all of the items already posted are dead-on, and the only thing I'd add is to use Valvoline racing oil - heaviest grade you can find. That's what I did and squeaked by.

Well, that and the 50-dollar bill I slipped the guy.

(oh wait - did I say that out-loud?

Mac.

lmao i didn't hear a thing

clinebarger · 03-03-2010, 05:28 PM

Quote:

Originally Posted by 74project

Failed on idle and high speed co output.

Is your truck equipped with a smog pump?

03-01-2010, 11:57 PM	#1
74project Registered User Join Date: May 2009 Location: Las Vegas Posts: 216	Won't pass smog. 79 chevy won't pass smog. It's been sitting for two years. I changed plugs gas oil and it runs better than ever. It's never not passed but now it's a problem. Any ideas on where to start?

03-02-2010, 12:18 AM	#2
bwood Registered User Join Date: Jan 2003 Location: Denison, Texas Posts: 1,919	Re: Won't pass smog. Not sure if I can help, but it would help to know what it actually failed on. The term "Smog" is kind of generic as they look for specific things and it only takes one of them out of range to fail. Did they give you a printout or readout showing why you failed. __________________ 1998 GMC Sierra SLE 1/2 ton 2WD 305 Vortec -Gibson Stainless Cat Back Swept Side -SS Wheels 2005 Honda CRF250R 2006 Honda CRF150F

03-02-2010, 12:53 AM	#3
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Re: Won't pass smog. Yea, more info is needed. Was the cat hot? Were you using the highest octane fuel you could buy? If the truck was parked for two years, you need to run it. Carbon buildup on the valves and exhaust pipe will hurt readings. Was the failure at low RPM, idle or high RPM? What emission equipment is on it? __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

03-02-2010, 01:03 AM	#4
74project Registered User Join Date: May 2009 Location: Las Vegas Posts: 216	Re: Won't pass smog. Engine was driven all morning on the highway. I did not put high octane in.

03-02-2010, 01:04 AM	#5
74project Registered User Join Date: May 2009 Location: Las Vegas Posts: 216	Re: Won't pass smog. Failed on idle and high speed co output.

03-02-2010, 01:08 AM	#6
74project Registered User Join Date: May 2009 Location: Las Vegas Posts: 216	Re: Won't pass smog. I was going to fill her up with some higher grade fuel what do you sugg? To help clean out the bad stuff

03-02-2010, 01:52 AM	#7
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Re: Won't pass smog. First, run a can of Sea Foam through it. You can buy it at any parts stores. What is your timing? Can you post the numbers between passing and failing? Is there a big gap? Do you know how to adjust a carb? You could run it a little lean to pass. Read this on using a vacuum gauge: http://www.centuryperformance.com/tu...e-spg-148.html __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

03-02-2010, 11:26 PM	#8
73chevyman Registered User Join Date: Nov 2008 Location: Lusby, MD Posts: 563	Re: Won't pass smog. if it where me 1 i would change cap rotor. 2 change spark plugs and the wires. 3 new pcv valve. 4 change the oil. 5 set the ildle to 1500 rpms and drip water in the carb so that all the carbon blows out the pipe redneck cleaning. 6 put 93 oct in with a bottle of octain boost and run the piss out of it till it runs out of gas fill it back up and go streight to the smog test it will pass with flying colors hehehehe.. what i've always done never had a problem __________________ http://67-72chevytrucks.com/vboard/group.php?groupid=37 73 C10 Fleetside If it ain't a Chevy it's foreign http://hotridesmag.com/

03-03-2010, 12:40 PM	#9
MacAttack 283 Drama Queen Join Date: Dec 2004 Location: Surf City, CA Posts: 2,435	Re: Won't pass smog. Had a straight-six Nova with the same issue and all of the items already posted are dead-on, and the only thing I'd add is to use Valvoline racing oil - heaviest grade you can find. That's what I did and squeaked by. Well, that and the 50-dollar bill I slipped the guy. (oh wait - did I say that out-loud? Mac. __________________ For about 12 years of my adult life I had a severe speech impediment. My ex-wife never let me get a word in edgewise.



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