Crackling sound

[Js32274]

I now hear an electric crackling sound when I push down on the gas peddle. Sound comes from the engine it Does not happen all the time. Just random times. What do you guys think? change spark plugs?

 

[L\Bronco]

Hey there Js, we need a bit more info, is there a running condition that accompanies the sound? (Shake, shudder or misfire?)
Could be plug wires arcing, could also be detonating, (pinging)
Let us know.
Hows the new paint holding up?
Cheers

 

[Js32274]

Usually it happens the first few minutes of driving before it is really warmed up well. Also tends to happen going uphill. No shake or rattle.
been real happy with the paint. Took it to the beach last week and that was a lot of fun.

 

[L\Bronco]

Thats awesome! Ive put about 3500 miles on my 79 resto mod, it is so much fun to drive, plus it sure turns heads!
Hard to say on yours without experiencing it.
Try a tank of premium, see if it changes, if so, it could be detonation.
(Pinging)

 

[Tiha]

I am really curious I cannot imagine what you are hearing. Should be interesting when you get it figured out.

 

[miesk5]

Yo Js,
As member L\Bronco advised.
I'm assuming a hight tension wire or the distributor cap may be may be the issue.

 

[Motech]

I'm thinking you're hearing an exhaust leak, especially if it's a 351M or 400. This would explain both qualifiers: under load and cold engine, as many leaks will seal up with heat.

Check, of course, your manifold gaskets and the flanges at the end of the manifolds. If equipped with air injection, check the air pipes, especially the rear cylinder head mounting gaskets, or even the pipe, check valves and hoses.

Also check the EFE valve down at manifold outlet. I forget what side it's on on those models, but it'll be sandwiched between the exhaust manifold and the exhaust pipe, with a vacuum diaphragm coming off of it. Has a valve in there that is only commanded closed when vacuum is provided through a thermal switch. That would explain why it goes away when it's warm too. It could just be flopping around.

EDIT:
A mechanics stethoscope is a cheap investment, and very handy for finding things like this. You would actually pull the probe out of the hose and just listen through the hose itself. Have an assistant rev it up for you when it's cold so you can find it easier.

Another EDIT:
If you do get yourself a mechanics stethoscope, pick up a two or three foot section of 5/16 steel fuel line. You can even bend the end of it a little bit, put the straight end into your stethoscope hose and have a heck of a lot more range and less chance of burning up your hose when you're listening to exhaust components.

 

[L\Bronco]

Good call Motech!

 

[Motech]

Good call Motech!

Thanks Canook!

 

[Motech]

Is this it? This is your Bronco?

That is badazz brah! I love that blue & white!

Got any top-less pics?

 

[NotaVegetarian]

Well have seen lots of different causes for this type of sound under lots of conditions.
could be spark knock from the timing be off just a bit, if it’s a stock distributor may try adding adjustable vacuum advance unit, may not be as common as in the 80s an 90s
exhaust leak , try retorque the manifold bolts, or change the gasket
have seen a bad coil or coil wire be the problem too.
check all the vacuum