when did GM put catalytic converters on Sierra 305s?
 

I bought my 1977 GMC Sierra with a 305 from a guy in Alabama about 4-5 years ago. Other than change oil,plugs, wires and brakes it's just the way I found it. i've passed emissions every year...except this year. All of a sudden they tell me it's missing the catalytic converters. I'm suspicious. Did these trucks even have cats? LMC doesn't list them in their parts. The two doofuses in the testing facility looked like couldn't make change from a twenty without a compter. Fumbled all over the truck looking for numbers, couldn't open the hood without my help. Frankly, I think I'm being railroaded.

Re: when did GM put catalytic converters on Sierra 305s?
 

I'm in middle Tennessee, by the way.

Re: when did GM put catalytic converters on Sierra 305s?
 

if GVWis 6000 lbs. or less you need a cat..

Re: when did GM put catalytic converters on Sierra 305s?
 

damm, tn is rough on emissions
found a link
http://www.tn.gov/environment/apc/vehicle/

Re: when did GM put catalytic converters on Sierra 305s?
 

I believe 1975 was the first year that they were required on 1/2 ton trucks.

Re: when did GM put catalytic converters on Sierra 305s?
 

I can confirm our '75 1/2 ton shortbox had a cat converter.

(It blew up and tossed it's contents all over the freeway).

K

Re: when did GM put catalytic converters on Sierra 305s?
 

Is the truck a Big 10 or Heavy Half? My 76' didn't have cats because it was a Big 10. The whole reason behind the Big 10's and Heavy Half's was to get around emissions standards as I understand it.

Re: when did GM put catalytic converters on Sierra 305s?
 

Thanks! Door tag says GVWR is 4900 so I guess I do. Just floors me that I've been passing inspection all these years (at two locations, mind you) with nobody saying anything.
Just aggrivating because I've got another vehicle in the shop already and I'm not all that fired up about paying the extra money right now.

Re: when did GM put catalytic converters on Sierra 305s?
 

Did it fail because of visual inspection. If so go to a junkyard, get a old one of a car, cut it open(top half/bottom half), wrap it around the pipe and weld it back on.

Re: when did GM put catalytic converters on Sierra 305s?
 

It started at about 2500 hydrocarbon with 500 being the limit. I put some seafoam and alcohol in some premium gas and gunned it to the next town down the innerstate. Figured this would do it. Imagine my surprise when I was told I was short a catalytic converter only two days after I was told that it was simply high on hydrocarbons!

Re: when did GM put catalytic converters on Sierra 305s?
 

was it one place that said you needed a converter? If so you might want to try another place that know what they are doing before you go through the trouble of getting a cat..

Re: when did GM put catalytic converters on Sierra 305s?
 

Don't feel like your alone...had some doofuss try to tell me the same for my '68! I had to laugh at the whole shop...as non of them knew it was 1975 models (for some '74) when things changed and regular leaded fuel was on its way out and unleaded was getting its start. Yes, from 1975 to 1980 there were both 1/2 tons and 5/8 tons (Big 10 and Heavy Half) sold. 1/2 tons had all the smog stuff....the 5/8 tons got HD hardware and no emissions.

Re: when did GM put catalytic converters on Sierra 305s?
 

This may help http://73-87.com/7387info/7387emislevel.htm