One of the most common causes of backfires is a bad spark plug or ignition coil. If there's no spark, unburned fuel enters the exhaust system and can ignite after hitting hot components.
The engine could also be running too rich, either from a bad ECU tune or improper carburetor settings.
There are other things that can cause backfires, like a bad catalytic converter or an exhaust leak, but for this one I'd check the spark plugs first.
This sounds like a hanging exhaust-valve to me - broken valve spring means that the valve isn't closing and, when the plug lights, what would be an in-chamber combustion event is going directly out the exhaust.
If it's a valve, you can hold a piece up paper up to the exhaust pipe. If the paper flutters or gets pulled into the pipe at all, you have a problem with the exhaust valves.
I had a beater truck that was off the road for a year or so, and when I started it it was doing a much milder version of this, just the occasional *chuff* of a misfire and not a lot of power. local shop changed all the plugs and 3 of the coils for a decent price; given it was a 5.4 triton I didn't want to mess with extracting broken plugs. engine's run fine ever since.
we should have sued ford over this. instead had to replace the engine on my own dime, only to have it do it again with an engine fire, burning the vehicle up in the process. super fun when you're on the highway and it does this.
zanaria
Stop sticking shotgun shells up your exhaust pipe...
GTPTB
This is my BOOMVAN!
lightfoot2
One of the injectors is stuck open, flooding the exhaust with gas, go boom.
sochilln
https://media0.giphy.com/media/v1.Y2lkPWE1NzM3M2U1NWh5M3AwMnRiejdxcmR2OGIxb2FuYXJhbTM2cHB0MWp4NnJsY3NxcyZlcD12MV9naWZzX3NlYXJjaCZjdD1n/24czIW9Kmp5AmCgnbK/200w.webp
fretno
Or crossed wires. It will blow out the muffler in one of those compressions. Boom
GreasyFingersSmearingShabbyClothes
Gesundheit
Vysard
So we didn't have any mufflers on hand, so I attached a shotgun.
foreverinchains
One of the most common causes of backfires is a bad spark plug or ignition coil. If there's no spark, unburned fuel enters the exhaust system and can ignite after hitting hot components.
The engine could also be running too rich, either from a bad ECU tune or improper carburetor settings.
There are other things that can cause backfires, like a bad catalytic converter or an exhaust leak, but for this one I'd check the spark plugs first.
flornholio
This sounds like a hanging exhaust-valve to me - broken valve spring means that the valve isn't closing and, when the plug lights, what would be an in-chamber combustion event is going directly out the exhaust.
foreverinchains
If it's a valve, you can hold a piece up paper up to the exhaust pipe. If the paper flutters or gets pulled into the pipe at all, you have a problem with the exhaust valves.
evenelectronicbrainpancakecrystalelderly
I had a beater truck that was off the road for a year or so, and when I started it it was doing a much milder version of this, just the occasional *chuff* of a misfire and not a lot of power. local shop changed all the plugs and 3 of the coils for a decent price; given it was a 5.4 triton I didn't want to mess with extracting broken plugs. engine's run fine ever since.
stonerhino
we should have sued ford over this. instead had to replace the engine on my own dime, only to have it do it again with an engine fire, burning the vehicle up in the process. super fun when you're on the highway and it does this.