Bucking and Muffler Explosion

[AC932]

Different post to address a different issue I suppose.

Truck is a 74 Bronco with a Stock 302, Duraspark ignition with an aftermarket NAPA control box. Spark plugs are Autolite 45's with ~13k miles on them. There's two fuel filters, one before the fuel pump, and one screwed into the carb. Fuel pump is mechanical, not sure how old. Oil doesn't smell like gas.

Driving down the highway at about 70, truck starts to buck. Try to power through it, bucking gets worse, engine will die for a good second, then come back for a second, then die, etc. Pull off the highway, foot off the throttle, and the muffler explodes. Now, truck is running fine at 60, but if I try to get up to 70, it starts bucking until I let it get down to about 50, where it recovers and can cruise at 60 again. Engine is smooth at idle, with a slight ticking that's been getting slightly worse over time.

Any ideas? My first thought was fuel delivery, but if it was starved that bad, would the muffler be able to gather enough gas to explode? Do the ignition modules/other components fail in this sorta fashion?

I'm probably going to throw a new fuel filter and plugs at it tonight, seeing as they're about due anyway. I'll put up pictures of the old plugs when I take em out.

Here's that ignition module:

 

[cldonley]

Sounds kinda like not enough timing advance-interested to see what color those plugs are when you pull them.

 

[blubuckaroo]

Mine did that once. Split the muffler from end to end! I thought it certainly had to be a bad Duraspark module. But the problem continued after replacing the module.
Turned out to be a bad mechanical fuel pump.
BTW, you only need one fuel filter. A second one won't make the fuel any cleaner.
If you think the screw in one is too small, get a barbed fitting for the carb and put the inline right there ahead of the carb.

 

[sanndmann3]

Mine did that once. Split the muffler from end to end! I thought it certainly had to be a bad Duraspark module. But the problem continued after replacing the module.
Turned out to be a bad mechanical fuel pump.
BTW, you only need one fuel filter. A second one won't make the fuel any cleaner.
If you think the screw in one is too small, get a barbed fitting for the carb and put the inline right there ahead of the carb.

Happened to me too with my Mustang. Exploded a stainless steel muffler...
In my case it was a bad coil.

 

[jckkys]

A filter between the pump and tanks is a bad idea. It invites vapor lock. I learned this the hard way. It gets worse in warm/hot weather. The HP needed to push EBs 70 MPH has over stretched the fuel delivery past it's capacity. Replace the ill advised filter upstream of the pump with piece of hose and see what happens.

 

[Broncobowsher]

Fuel is good. As proven by the right mix in the muffler as it ignited. Spark issue. Weak coil?

 

[AC932]

Well, took the plugs out, they all look the same.

Gapped new plugs at ~.45. Also removed the filter between the pump and tank, and replaced the filter screwed into the carb. If that didn't fix the issue, I'll see about getting a coil in the next couple days.

Thank y'all again for the suggestions!

 

[Rustytruck]

Do the ohmm check on the mag pickup in the distributer. More mag pickups fail than good modules.
un plug the distributer, ohmm check between orange wire and purple wire. Should be between 400 to 700 ohms. Check for contintuity between the black wire and orange wire or black and purple wire there should be no contintuity . Dont buy cheap ignition components.

 

[garberz]

This happened years ago to me on my 76’ F-250, turned out to be a faulty coil wire.

Mark

 

[AC932]

Managed to get a new coil thrown on there. Some combination of that, the new plugs, and the fuel filter solved the issue. I might go back to the old coil just to see what exactly the cause was.

Thank y'all for the help!