[whwright]

Hi again guys. I hope your holidays are going (or went) well.

You may recall that I have a 1986 Chevy half-ton with a 305. It has always seemed like a real dog, but lately it has gotten a lot worse, practically overnight. I have already done the tune-up, carb overhaul, etc. etc. and all that stuff still checks good.

So I pulled the exhaust pipe off the left manifold and -- HOLY COW! It's no speed demon, but at least it will get on the highway comfortably. It drives like a different truck.

I took it to a muffler shop, and the guy told me that somebody in the past put on the wrong type of converter. It is supposed to have a "backpressure EGR" converter, and they put on a "regular" converter. To make matters worse, he claims that the emmission controls are now damaged by the wrong converter (not enough backpressure at first, and now too much backpressure due to the fouled converter). It had something to do with a check valve on the A.I.R. system. According to him, the fouled converter also explains why I had to unhook the EGR and A.I.R. stuff to get the engine to idle.

Well, according to the muffler guy, if he puts on a new converter (it doesn't seem to matter if it's the "right" converter or not), it will just get "burned up" by the emmission control system problems.

Does any of this make sense to you guys? Is it all consistent?

Thanks.

Wayne.

 

[wyldman]

Glad to see you found us Wayne.Welcoome to the new site.

There is no such thing as a backpressure EGR cat.There are basically two types,as two way catalyst and a three way catalyst.Your truck should have had the three way type,which was a large pellet style convertor.They never plug up.The only problems they ever suffered were internal meltdown,and the pellets falling out due to the plug rusting out on the bottom.

The AIR system may have led to an early failure of the cat,by injecting too much air into the exhaust,and overheating the catalyst.EGR problems will not cause a cat to fail.A failed cat may affect EGR operation though.

Put the cat on it first.The pellet style aren't very common anymore,so a newer honeycomb style would replace it.

If you don't need the EGR or AIR system hooked up for emission purposes,then leave them disconnected.It won't hurt anything.

If you need any more info,just let me know.

 

[sonjaab]

GH......Don't know if your state requires a cat on the
truck for emission or state inspection like here in NY.

But I think the guy is full of BS !

GM is funny...They make 1 part to fit most of their models!
Heck a 6 bolt wheel off a 75 chevy will fit my 97 chevy!

Drop the exaust in back of the converter. Get a piece of
pipe and "hog" out the inside of the cat !

Prob. solved and the truck will appear "stock" !

I have done the same thing with a few of my older 75 and up
GM winter rats with clogged converters !........geo

 

[whwright]

Thanks for the help guys. As usual, you are awesome!

I called the Oklahoma Department of Motor Vehicles, who told me that 1986 models are "emmissions exempt." Upon further probing, this simply means that they are not subject to any type of sniffer testing, only visual inspection. The visual inspection will only occur if a Highway Patrolman elects to pull you over to make sure the vehicle hasn't been "altered."

I have never heard of anyone being pulled over for a visual inspection, so I'm simply going to pitch the converter. The muffler shop will install a "test pipe" for $30 or a new converter for $140. It doesn't take a rocket scientist to do the math.

Thanks! And Happy New Year!

Wayne.