Its a 1999 Ford f150 with 5.4 V8.

My wife was at the grocery and just a few seconds after she started it to leave, it started missing and "jackhammering/sucking/backfiring sound was comming from the back of the engine...

After school, I went by the truck and it was still making this viloent sucking/backfiring sound....

My first thought was that a spark plug had "poped out" but I would imagine that there would be a gas smell, and I would be able to see it spraing outta the area...

So I have no clue what the deal is....

I shined the light all over the engine, and seen nothing outta place... no engine lights either...just the horrible jackhammering/sucking/backfiring sound...

The noise does relate to rpm by the way....

Any suggestions????

 

check the coils. you may have had one go bad.

 

I have a 4.6, my head gasket is leaking and sounds alot like yours. I changed my plugs a few weeks ago thinking that was it or wires, one plug was completely empty inside, nothing, I assume the guts went out the exhaust, I hope. Ran great for a while then started again, found leaking head gasket, burning AF. I'm trying to confirm recall info on mine (see my post for help this morning).

 

I had the same thing happen to me,it was a slow leak from a hose leakink down on top of the coil and spark plug.It was the furthest plug back on the passanger side.Good Luck
MOEDADDY