Blown/ seized or detonated Ford F250 390 1969

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Titangree1

New member
My brothers truck is a beautiful 1969 Ford F250 custom (single) cab, with a 390 and about 25k on the motor and 3k on the 4 speed ******. But the original dual exhaust was cut off basically at the headers giving it a mean growl. After a few tickets since we lived in Idaho before, we put straight pipe 3 or 4" stainless to glass packs back to straight then 8 inch tips. The whole thing is dual from the headers, never connected. But once the exhaust was in I knew the carburated motor would have to adjust fuel to air ratio because of the restriction now on the exhaust. So instead of started it and putting around to listen he tuned it up and every time he left off the gas driving around it would backfire like a semis air brake, buh buh buh buh. And then all of a sudden boom! It sounded like a shotgun went off in the cab. Towed it home and he left for the navy. Any reasons what could have happened or why it would have?
Thanks
 
I would look at the plugs first. It may have been too lean and or the timing is off. The plugs will tell you if a piston has detonated by aluminum splash or the electrode is gone. With the plugs out, turn the engine 360* to see if it is locked up. If it's free, give it a compression check on all 8.
 
I had that happen on a new Chevelle I bought in '69 it was a bad distributor condenser the muffler exploded and looked like a banana peel had 89 miles on the car so warranty covered the fix and a tow.
 
Did you/he try to start the engine afterward, or not take a chance on making something worse?

If the mixture is a touch rich and you let up on the gas pedal when driving you can get enough un-burned fuel fumes built up in the exhaust system it can go off and blow apart the new exhaust pieces it didn't have before.

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I've never had an engine blow up when I was off the gas. On, yes. I'd look at the exhaust and see if dmsfrr isn't right. I've got an OT car, fuel injection, with a race computer and no fuel shut off on closed throttle. It'll pop some on a long steep downhill, just like a carb does.

I mean, if it cranks and starts, it's probably ok. If it is, you can fix it and drive it like you stole it.
 
A worn out timing chain can slip when letting off the gas,
or can slip as you shut the engine off. ;)








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