CAmaninacan

ok first and foremost theres a code for multiple misfire however a local mechanic said cylinder one was at fault he said all my delteq ignition was good he was worried about the exhaust valve being faulty but i didnt have enough money to pay him to look more into the issue i popped off the valve cover and everything underneath seemed to be ok however when i put the cover back on and fired it up theres a loud clank noise it seems to be evenly spaced out like a rod knock but at the same time its mostly heard underneath by the cats and dissapears when you give it alittle gas and thats about it what are my failure points here???

if you would like to see a video (with audio) of the car in its current state pm me

leesvet

dead cat.

The chunk of catylist breaks apart and rattles around under low rpm. As exhaust flow increases it forces the chunks against the outlet and they stop rattling. They come apart and fill the mufflers with debris causing the mufflers to plug and plug the entire system if not address real soon.

You should be able to tell if the rattle comes from a cat or the engine block. Get a length of 1/4" or 3/8" hose and listen to the block as it idles. Then listen to the cats. Use 5/8 hose if your ear is that big

CAmaninacan

it definitely did seem like it was the cats how do i "address the issue" drop the exhaust and dump it out?????? also does this have influence on the misfire whats my issue there? timing?

1963SS

Yep, a clogged cat can certainly cause P0300 type code or whatever a random multiple cylinder misfire is. Also what led the mechanic to believe that there was an issue with the exhaust valve? Go to Harbor Freight and buy a compression tester if you believe there to be a problem. They have one for about 12-13 bucks.

If you can change a spark plug you can do your own compression test. Sometimes the piece of mind is worth it.

aminnich

What year car is this again? Heading says 96, but then your personal info says 89.?

CAmaninacan

the 89 is my brothers mine is a 96.

wow thats great news i didnt even think a cat could cause a code like that
oh he said cylinder 1 was getting 15 idk if he even tested the others or what its suppose to be

CAmaninacan

wait what caused the cat to blow?? come to think of it i think the noise showed up awhile after the code showed up?

leesvet

dont brain-***k it to death .....just take the facts and address what you know. One thing at a time. The compression tester will help with that. I have that particular tool from harbor freight and it works great...

You can play whadda coudda if, next week when its fixed.

Sometimes a coincidence is just a coincidence...

Cats just break sometimes. I've had it happen a couple times. IF that is what is rattling, clean it out or replace the cat asap. The chunks will cause even more trouble if allowed to blow into the mufflers where they cannot be dumped out....

CAmaninacan

haha alright i just dont get why the code is there but i will replace the cat asap thanks all for the advice ill repost how it went when i finally have the time to follow up

383vett

So far everyone seems to think it's a converter problem. The op says the knock is evenly spaced like a rod knock. Why would a converter gone bad have a sound like a rod knock? Maybe it's a rod. The converters are near the pan in most of these cars. Just say'n.

CAmaninacan

im asking because idk.... does a rod knock stop making the knocking noise when you push on the gas?

1963SS

I wouldn't change the cat yet. There's not enough info to make that decision. I only said that a cat could cause a P0300 code. So could a lot of other things. I'm curious how the mechanic made the determination that the exhaust valve was faulty.

Can you post that video of the noise and kinda move the camera around some. Cats don't usually sound anything like an evenly spaced knock.

As leesvette mentioned, take a piece of hose and make a hillbilly stethoscope. Stick on end in your ear and probe around the exhaust, valve covers, oil pan, etc with the other end of the hose. It's amazing how well that works. You should be able to come closer to pinpointing the noise.

CAmaninacan

i tried the ghetto steth. with a hammer but i couldnt tell there was more vibration in the cats but still alot in the pan

as far as video goes how do i do that ill just pm you my email and send you the vid that way

383vett

Cut open your oil filter and see if there is bearing stuff in there. If you have a rod knock, it'll be obvious.

CAmaninacan

cut up the filter rand the oil through cloth haven't had time to remove the pan yet there were no flakes that i saw should i pursue the pan??

leesvet

Generally if there was a spun bearing, a bad small end rod or big end, any bearing damage/failure there would be a silverish gel or grit in the oil that would like unmixed silver paint.

So you did'nt see anything in the oil...thats good news. Now assuming that its rythmic from a rotating assembly the trick will be to isolate where..then you can figure what.

Like '63SS said, broken cats don;t rattle consistantly...they kinda rattle without a rythem...random.

You could have a valve train issue, bent or broken pushrod, collapsed lifter, or even a bent valve (but thats a big ?? in its own right). Don't take much to bend a valve and make it bang around and cause loss of compression. I bent one as small pieces of a broken piston tried to exit and got caught as the valve spring tried to close the valve. Bent it real good too...Sits on my bookshelf as a reminder, right next to the piston with the missing ring glan...

back to your problem...
I'm still thinking a compression test would help direct further exploration. If its low...and a squirt of oil does not make it go up, its a valve. If oil helps the psi go up, or increase, its a piston.

If you find there is NO compression issue, then its back to external (outside the pan) rotating assys....torque converter & bolts, balancer (looked at that?) and flywheel. I have had a chunk of a delco starter break off inside the cover and beat around in there and that sounded like someone beating a 55 gal drum with a bat. It was not exactly a perfect rythem but close...everytime the flywheel teeth would grab that chunk and fling it against the aluminum cover, it made a helluve noise. Bounce off and get grabbed again and repeat...about 3 times a second at idle. Because the starter still worked it took me a few nervous minutes to figure out what was going on.

CAmaninacan

haha "nervouse minutes" ive been nervouse ever since i got the first reply to this post... in the very bottom of the filter there seemed to be some grey "stuff" i couldnt tell what it was there was no metal associated there wasnt much maybe the equivelant of half a drop of water idk i just ordered a compression tester at this point what should i hope for a bad bearing or valves (i know it wont matter what i hope but both are scaring me)
my oil is sitting in a milk jug right now (lol) too dark to really see through but a cant see any sludge on the bottom i guess ill update when i get the tester or drop the pan -__- why me lol such a beautiful vette so much fun such a shame lol hey one quick question does a rod slowly get louder and louder or is it all the sudden one day it decides to bust and start making a crap ton of noise? mine seemed like one day it showed up and the very next it got to wear it is now....

aminnich

Get an oil sample done next.

CAmaninacan

where do i get that done at what will it tell me? if i have chunks in my oil? what if i ran a magnet through it is the metal chunks magnetic

aminnich

Check with your local auto parts store about oil analysis. Also do a 'google search' about oil analysis and you will find it can give you all kinds of good info about your engine condition.

Where are you located?