Help identifying pinging/rattling

[fdbdw]

I have a pinging/rattle coming from my left bank exhaust about mid way down the exhaust pipe. Timing is good, A/F ratio numbers are good. Checked plugs and wires, all good. Happens at idle and low rpm but not all the time. It is the same exhaust side that has an O2 sensor, not sure if that is creating the sound some how. I’m at a loss, any experience, thoughts or ideas would be appreciated

[Steeveedee]

Do you have an H- or X-pipe? If so, you could try blocking that side of the exhaust and see if the noise goes away. It could be a loose baffle in the muffler.

[Sparky dave]

If it’s deffo not detonation. Have you a bolt loose in there or something

[fdbdw]

Originally Posted by Steeveedee

Do you have an H- or X-pipe? If so, you could try blocking that side of the exhaust and see if the noise goes away. It could be a loose baffle in the muffler.

Straight pipes, new mufflers, definitely coming from the left bank. Crawled under there again today can’t find anything loose or dangling that would make any noise. I’m baffled

[geezer#99]

I put a set of headers on once and had the muffler shop weld the collectors to my pipes. After welding he used a cut off wheel to remove the excess pipe inside the collector. A small half round piece of the pipe somehow fell down inside where he couldn’t get to it. Bolted it up and figured I’d never know the difference. That little piece was floating around near the muffler. Sometimes it rattled, sometimes it didn’t. Just like yours. Ended up pulling the muffler off and finding it right there. Used some long needle nose pliers to snag it.

It’s those little things that drive you nuts! LOL!!

[Steeveedee]

FWIW, I've seen brand new cars with broken baffles in the muffler. I'm not saying I'm right, it's just something to check. After seeing geezer#99's post, it occurs to me that you could use a mallet and tap the pipe and muffler to see if you can duplicate the rattling noise. I found a case where a car had the oil light flash when doing hard braking. Turned out that the oil pickup screen had fallen off the pump. I hit the pan with a rubber hammer, and could hear the screen plop back down onto the pan. That's one rare failure, right there!

[fdbdw]

Still chasing this issue, new plugs, wires , even bought a new distributor thinking it may be
The issue. Check me out on this, I was thinking possibly predetonation, kept backing the timing off, ended up at ridicules ATDC numbers. Then decided to go the other way and it seemed to get better. Any chance I was to far retarded and that would cause a pinging sound in the exhaust? I feel like I have a good knowledge base on timing and tuning but this is driving me crazy.

[Steeveedee]

Sufficiently retarded timing can have the fuel still combusting when it leave the cylinder. Without reading all the way through what was written previously, have you verified that the timing mark on the harmonic balancer is indeed indicating TDC when #1 cylinder is at TDC?

[clay68c10]

Yes that is possible. I was running a very conservative timing table on the caddy at first, worried about pinging the stock hi compression pistons. I was getting the same noise, with the occasional exhaust backfire when my VE tables were too rich (usually in PE mode). I advanced the timing a few degrees and got my fueling right, no more noise. Engines definitely sound weird without enough advance.

[fdbdw]

Originally Posted by Steeveedee

Sufficiently retarded timing can have the fuel still combusting when it leave the cylinder. Without reading all the way through what was written previously, have you verified that the timing mark on the harmonic balancer is indeed indicating TDC when #1 cylinder is at TDC?

I did verify TDC, but I’m going to re-check it along with everything else.