cat on my 1979

[Big Blue]

Just got my truck inspected, The garage guy said I should have cats on my exhaust. How can I tell if my truck needs them. When I got this truck it had none. I know over the years people took them off. Maybe that is what happened to mine. He still inspected the truck because the mileage was under 5000 miles since last inspection. Any help, Thanks, John

[Tom]

Call GM parts department and give them your vin. Thats all it takes.

[barry1982]

Not positive about American trucks, but by 79 all of the Canadian trucks I have seen came with cats. I believe there were a few exceptions.... 1 tons , and heavy 3/4 tons.

[74CustomK20]

It depends on the trucks GVWR.

[Valarius_Starchaser]

GMs VIN based cataloging started in 1990 calling a parts department won't help

[oldpurple]

Originally Posted by barry1982

Not positive about American trucks, but by 79 all of the Canadian trucks I have seen came with cats. I believe there were a few exceptions.... 1 tons , and heavy 3/4 tons.

I have a low km untouched Canadian '79 and I'm pretty confident it never had a cat. It is a heavy half though so that may have something to do with it.

[ironroad9c1]

in the US I know up to 86 if its under 8,599gvwr it needs a cat, 8600 and above did not have a cat. My 86 C6P 3/4 didn't have one because it was rated 8600 GVWR.Also you should have a sticker on the rad support that will tell you what pollution control devices it had, Air,egr, catalist ect.

[Big Blue]

Thanks everyone, sure is a lot to know. Since he inspected the truck do I really need one?
John

[Alex V.]

If it's legal the only reason you "need" one is if it's a nuts-and-bolts restoration and you're worried about what's "original" to a fault. Otherwise, especially on a carbureted truck, there's no benefit to it. I'm not as familiar with emissions equipment in the 70's, but as ironroad9c1 said, trucks 8,600 GVW and over (which was most decently-optioned 3/4 tons and nearly all, if not all, 1-tons) didn't have to have cats in the mid 80's. From what I've observed most, if not all, states only require such emissions equipment as came on a particular vehicle from the factory.

[95 S_Trucker]

If you plan to drive less than 5k a year, I'd leave them off. I have my pa emissions insp license and am in the same emission tier as you.

[Tom]

A quality high flow cat certainly won't hinder flow at all so if you need them then put em on it won't hurt anything. My 79 1/2ton 2wd required them. My 78 1/2ton 2wd does not.

[Keith Seymore]

Originally Posted by Tom

My 79 1/2ton 2wd required them. My 78 1/2ton 2wd does not.

I'm surprised to hear that.

Our '75 swb 1/2 ton 2wd had a cat on it.

It blew the bottom out and scattered the little pellets all over the highway.

K

[Nontwisty396]

I spent a decade in the exhaust business. Yours was a common question. Everyone (mostly) has steered you in the right direction.
The 2 most common and simple ways to tell is look for the emissions sticker, it will say "catalyst" or "non-catalyst" on it USUALLY.
The other simple way is to look under the truck. If there is a large (possibly wide oval shaped) heat shield above the exhaust around the rear of cab to front of bed area it likely had one.
IF the exhaust is original, look about 3 feet back from the manifold to see if there's a newer section of pipe around 2 feet long. That would indicate a "sub-pipe". But as said, most 3/4 tons and up didn't have one. And as mentioned, the newer hi-flow cats don't really hinder performance, especially when installed as a pair on dual exhaust. Spendy, but looks nice and balances sound as well.