Advice/ help please, engine noise Options

[r_towle]

Muffler leaking….be more aggressive holding a board over the tailpipe (s) and force the leak

Or
Smoke test the intake and look for a leak in the plenum or any vacuum lines.

A smoke test (google it) can be done with a cheap Halloween smoke machine….you are filling up the intake with smoke to see if it leaks out anywhere.

With these 50 year old plenums, I have seen rust holes open up in the bottom of the plenum where you cannot see it, and you can’t get your hand down there.

You are looking for unmeasured air here.
There are three places
Intake
Air injection
Exhaust

Rich

[emerygt350]

These 4s will idle with a plug off no problem. You may want to just try driving it while the plug wire is grounded to the block or something. See if it changes anything. If you notice no difference, you have a dead hole. A new cap and rotor never hurt anyone. If that doesn't cause a change I think you do need to go for the leak down test.

To do the leak down, you need to put it that first cylinder at TDC, put it in 5th gear (5th gear is good for rolling the car into TDC as well). Full on parking brake. Chock the hell out of all the tires, or even push it up against a wall (with a tire as a bumper). Then do your leak down of cylinder one.

[rgalla9146]

The car idles ?
Raise the idle to 2000 RPM and disconnect one fuel injector at a time.
The cylinder that goes quiet has the issue.
Head seal, exhaust leak, tight or leaking exhaust valve