1987 Chevrolet 350 tbi high idle

[AuroraGirl]

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It also appears we both have slip yokes that sit a little far out for comfort, if i understand correctly.

The clamp is also not squarely on your pipe to the rear visibly. I wonder if its not leaking intermittently and the pressure changes might be having small effect on running consistently but the noise maybe from that

 

[Bextreme04]

It looks like just single 3"... that's pretty standard for 200-350hp. That sure looks like a universal style cat... way back behind the transfer case. Which is WAY too far back. The older trucks had them back a little bit, but they were the pellet style so they didn't need to get the honeycomb as hot to work. Newer style cats should be much closer than that to the engine. I would definitely disconnect the exhaust right before the cat and see if you suddenly have a much better running engine and no more weird noises coming from your exhaust. I bet that cat is completely plugged up.

 

[iamtherealJayy]

The tachometer is green wire off the hei distributor similar to the blue k10, I just asked dad about the catalytic converter he didn’t provide any useful information. I’ll look into what it does without it. Would a clogged cat be part of the reason the truck is literally screaming by 3000 rpm?

 

[AuroraGirl]

It looks like just single 3"... that's pretty standard for 200-350hp. That sure looks like a universal style cat... way back behind the transfer case. Which is WAY too far back. The older trucks had them back a little bit, but they were the pellet style so they didn't need to get the honeycomb as hot to work. Newer style cats should be much closer than that to the engine. I would definitely disconnect the exhaust right before the cat and see if you suddenly have a much better running engine and no more weird noises coming from your exhaust. I bet that cat is completely plugged up.

Yeah, my bad. I guess just looking at the exhaust to me it seemed over 3 inches. but i trust your judgement on that. the 3 inch pipe ive used for my car looked a lot thinner but it was a long time ago lol.

But that is true, I didnt consider the heat part that far back. I knew that was where the original went, but that became a big issue for emissions testing in the 90s when honey comb types were on the scene especially for small blocks in cars, fords had issues too, where at idle the cat cools down too much and it may even drop into open loop

THen you started see them mount right on the back of the manifolds where htey collect often times.

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heres my cars bread loaf. That pipe connecting into it is only like 14 inches away from where the back manifold/crossover/ dump down into the exhaust on my fwd car.

 

[AuroraGirl]

The tachometer is green wire off the hei distributor similar to the blue k10, I just asked dad about the catalytic converter he didn’t provide any useful information. I’ll look into what it does without it. Would a clogged cat be part of the reason the truck is literally screaming by 3000 rpm?

it could be, i think when plugged cats are concerned, basically you cant exhaust flow right and that would, i suspect, make the o2 sensor if youre in closed loop read wrong and that would make your computer think it needs to correct or something. these days the o2 is fairly often before the cat and of course one after(for lifetime monitoring of its efficiency) but some cars do manifolds or other setups, but GM its common for the modern era to be shortly after the collection you have o2 and then shortly after the cat. based on where yours is, thats too cold to probably ever if maybe just not often get up to temp right id think

 

[iamtherealJayy]

I’ll get a better location photo of the cat, and the exhaust pipe diameter. I know the tips are like 3.5 or 4” diameter.

 

[iamtherealJayy]

With the tbi system is a catalytic converter required? Or could it be removed like on my carb 350?

 

[Bextreme04]

With the tbi system is a catalytic converter required? Or could it be removed like on my carb 350?

A cat is never required by the FI system. A TBI doesn't even have a second cat to be able to tell the difference. Modern system would need to have the secondary cat emissions codes removed in order to not throw a check engine light if the cat is not in the system.

That being said, I would keep the cat if it isn't plugged. My suggestion is for troubleshooting purposes only. Disconnect and see if it significantly improves the performance. If it does, you have a plugged cat or muffler.

 

[AuroraGirl]

With the tbi system is a catalytic converter required? Or could it be removed like on my carb 350?

You can remove it. just your O2 needs to be somewhere it can be up to temp, a heater o2 conversion is usually wise. In my experience, GM EFI without a cat doesnt make for much fuel smell left over like a carb vehicle may, but that was Sequential port fuel injection, not TBI. I suppose if its running the right mixture then its only at the mercy of fuel that comes out of the injectors and may evaporate or whatever but that isnt any different than with a Cat

 

[AuroraGirl]

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heres what both of my mufflers on my old aurora looked like
I never knew it had no mufflers actually doing anything until i cut them off and it was of no change to anything. The resonator was doing all the work lol.
That started life as a stainless steel muffler

 

[iamtherealJayy]

@Bextreme04 what is your reasoning for wanting to keep the cat? And @AuroraGirl the truck had an eye burning aroma while filming the exhaust the other day.

 

[Bextreme04]

@Bextreme04 what is your reasoning for wanting to keep the cat? And @AuroraGirl the truck had an eye burning aroma while filming the exhaust the other day.

Well, its supposed to get rid of that eye burning aroma...

I don't really care if you keep it or not. My point was just that there is no reason to get rid of a perfectly functional one. They do reduce the smell and take some nasty stuff for the environment out of the exhaust. I wont have any on my fuel injected 454, because I don't have any and it's not worth it for me to buy them just for the truck. If I already had some, I would put them on though.

My concern is that yours might be bad. If its a pellet type, I wouldn't put it back on. Its going to be ancient and likely doesn't work at all and is plugged up. If it is a honeycomb type and isn't plugged, put it back on but move it to as close to the pipe merger as possible.

 

[iamtherealJayy]

I’ll go get some better angle photos to show. I don’t know the first thing about catalytic converters other than everyone steals them for some reason

 

[AuroraGirl]

I’ll go get some better angle photos to show. I don’t know the first thing about catalytic converters other than everyone steals them for some reason

If yours is bad, steal it yourself and bring it to scrap yard. your wallet would be thicker. (thats why they are stolen. 2 seconds and a saw zall and a bad moral/ethical decision later and youre holding money from someones vehicle.)

Ive seen a shop that sold someone a cat (unsuspecting older folks) and they clearly punched out the guts and then installed the body of it because there was no insides when the car died and a friend cut those off to quickly part some of its valuables. The thing has 3 and makes me wonder if they did that to the others(I wasnt around for those)

what we are saying is all true here, bex is just giving you the basic laydown of what a pragmatic environmentally and personally aware person would say.

ie, do you want to reduce exhaust smell or gas smells, help the environment, and already own a cat?
If then, do you own a cat which has not degraded badly or plugged or been damaged?
If then, do you want to keep it working right?
if then, mount it forward in the exhaust stream(as he pointed out) and that will help
if not, then you would be best to scrap it and your choice to install one back into it (environmentally good, smells better, but costs $$. thats where he, or I, would then choose not to get one because of the prohibitive cost)

bex is proof that you dont have to be a hippie to make decisions best for the world, but also isnt a ghoul who would run without one to "stick it" to someone, presumably a caricature of someone online never met. I like to think a lot of people, truly, would be like this. As long as the personal burden or costs arent so much, we can make decisions that are good for everything.

however the pellet type comment is also a good one, if it was like those then its best to remove. iirrc those cats tended to be more circular than flat, but i could be thinking about a particular example rather than a rule.

 

[iamtherealJayy]

I agree with bextreme about the environment and that’s perfectly fine I didn’t know if he had a particular reason such as it ran better. I won’t purchase one if this ones junk either honestly.