Diagnosing Exhaust Sound

[Slap Stick]

Just because the timing light says there is fire in the wire doesn't mean the plug is firing.
And you axed how high octane can make an engine run worse so, here goes.
Regular fuel is formulated to burn at about 400° C. Premium at about 500.
Higher octane fuel actually burns slower, reducing tendency to ignite prematurely. With lower compression premium fuel can still be burning while the exhaust valve is still open resulting in burned exhaust valves.
Also the slower burn can result in an incomplete burn, increasing deposits.

BTW, avgas octane is calculated differently than mogas so 100LL isnt the same as 100 octane race gas.

 

[Dan The Man]

There's a really odd burble to the exhaust note for a 440 for sure....if it isn't ignition, well....
I'll leave it to the more knowledgeable engine guys here,
Maybe it's time for a fresh video?

Just because the timing light says there is fire in the wire doesn't mean the plug is firing.
And you axed how high octane can make an engine run worse so, here goes.
Regular fuel is formulated to burn at about 400° C. Premium at about 500.
Higher octane fuel actually burns slower, reducing tendency to ignite prematurely. With lower compression premium fuel can still be burning while the exhaust valve is still open resulting in burned exhaust valves.
Also the slower burn can result in an incomplete burn, increasing deposits.

BTW, avgas octane is calculated differently than mogas so 100LL isnt the same as 100 octane race gas.

Damn, I just changed all the plugs and have the scars to prove it. What are the odds that one or more plugs are not firing AGAIN (old and new)? And if so, what would cause it? Coil, pu, cap, rotor all check out. And I'm assuming if the ECU is bad, it would not start at all. They say not to pull plugs wires one at a time on electronic ignition, but what choice do I have? Thanks for the lesson on octane. Its still in the can.

 

[Don Frelier]

They can run lousy with a "kind of bad" ecu. My brother had it with a couple ECU boxes.

They say not to pull plugs wires one at a time on electronic ignition

You can pull individual wires with electronic ignition.
If that were true then if a plug wire fell off it would ruin your ignition? (No)
That would be a lousy design.

 

[1967coronet]

Check your ECU for good ground.

 

[1STMP]

69 Charger 440. Finally got the beast running, but I don't like the "motor boat" sound coming from the exhaust https://app.photobucket.com/u/stump...941f16/p/fdc4576c-e08d-4004-b8e4-7f9c90e01cf1. The entire exhaust is "new" as in never exposed to the elements and always garaged since installed new. The heat riser is just loosey goosey, but I have it tied off counter clockwise to always be open. I just starting using Rec 90 ethanol free gas. Still tuning the carb since I rebuilt it so haven't road tested yet. What do you think?

I haven't seen anyone here mention the fuel
pickup tube screen may be clogged and
full of crud. Especially if it sat for five years
with fuel in the tank. Was the tank removed
to drain it, or was it siphoned out? Old gas
along with sediment in the bottom of the
tank turns into a sticky, gooey mess, and
adding new gas won't get rid of it.

 

[Dan The Man]

I haven't seen anyone here mention the fuel
pickup tube screen may be clogged and
full of crud. Especially if it sat for five years
with fuel in the tank. Was the tank removed
to drain it, or was it siphoned out? Old gas
along with sediment in the bottom of the
tank turns into a sticky, gooey mess, and
adding new gas won't get rid of it.

Quite possible, as I just drained the tank and added fresh fuel. I have a glass filter and the fuel looks clear and clean. Just not wanting to drop the tank and if its possible to change out the pu without dropping it, I would go that route.

 

[Don selleck]

pull wires while its running with some insulated pliers, etc. one at a time, if yours idle changes, cylinder is firing. If it doesn't remove that plug and see if the plug is actually sparking. the spark will jump up to an inch or so, so beware, it'll light you up looking for a ground.

 

[toolmanmike]

Wow, 3 pages and it still isn't fixed?

 

[dadsbee]

I'm laying odds it's just the way the exhaust makes it sound..

 

[Don selleck]

if there all good then check grounds, and connections, then change the box. imo

 

[Dan The Man]

Wow, 3 pages and it still isn't fixed?

Hey guy, I don't spend 24/7 working on my cars. Besides, I'm in blistering hot Florida while you are are in Iowa. Cut me some slack.

 

[toolmanmike]

Hey guy, I don't spend 24/7 working on my cars. Besides, I'm in blistering hot Florida while you are are in Iowa. Cut me some slack.

It's as frustrating for us trying to help as it is for you trying everything under the sun to fix it. We can't see and hear what is going on so all we can do is throw some darts at a board. So far all have stuck in the wall it seems.

 

[1967coronet]

I'm laying odds it's just the way the exhaust makes it sound..

If everything else is checking out dadsbee may be on the right track.
Just this past year I had a flow master 40 come apart inside.
Dan, if you have headers or a place to break the exhaust before the mufflers ???.
You never know. After that long nap there could also be a critter nest in a muffler.

 

[Dan The Man]

If everything else is checking out dadsbee may be on the right track.
Just this past year I had a flow master 40 come apart inside.
Dan, if you have headers or a place to break the exhaust before the mufflers ???.
You never know. After that long nap there could also be a critter nest in a muffler.

It could be the exhaust. I was listening to 69 Charger 440 exhausts on YouTube, and a few sounded like mine. I'm narrowing it down with all your help. And let me also apologize to everyone, especially toolmanmike, for being a dick. You guys are offering great advice and I'm just frustrated with all of it. Sorry guys....

 

[dadsbee]

My Bee and Bird, 383 and 440, for reference sound. Bee full stock exhaust from ECS (sounds just like it has it's entire life) and Bird close to stock but no H pipe with Chrysler New Yorker mufflers that we put together 31 years ago.

 

[oldbee]

Hasn't been said yet, but maybe you have some water in the gas? Add a can of dry gas to the tank, a cheap try.

 

[toolmanmike]

It almost sounds like it's idling off one side of the carb. I wish I was closer, I have a tach/dwell meter that can cancel cylinders one at a time or odd or even. Very handy to diagnose this sort of a problem.

 

[Dan The Man]

It almost sounds like it's idling off one side of the carb. I wish I was closer, I have a tach/dwell meter that can cancel cylinders one at a time or odd or even. Very handy to diagnose this sort of a problem.

I have a tach/dwell meter. How can I do that?

 

[toolmanmike]

I have a tach/dwell meter. How can I do that?

A standard tach/dwell doesn't cancel cylinders. You have to have a specific one that does.

 

[Dan The Man]

A standard tach/dwell doesn't cancel cylinders. You have to have a specific one that does.

Lets say it is idling off one side of the carb, what would I look for? I rebuilt the carb with the 1477 kit and replaced everything the kit had to offer. Simple and straight forward. I may be a dick at times, but I am mechanically inclined