*also posted in the Engines forum

On the way home from work today my 98 Exp w/5.4L (and 90k) started making a loud banging noise, coming from engine compartment, almost like a machine gun, varying with engine speed. No warning lights, oil pressure fine, didn't run rough, no loss of power, just the loud bang. The noise was a bit intermmittent, bang a few times, stop, bang a few more, no real pattern, but giving it a little more gas seemed likely to make it start. Didn't bang much at low RPMs, hardly at all at idle. I was maybe 200 yards from home, slowly cruised on in.

Anyway, I've read some of the blown plug threads (no pun), but it doesn't seem likely, unless it's still hanging in there and I'm just hearing the combustion through the gap. I opened it up in the driveway, found one vac elbow that had a small crack, fixed that, but it obviously wasn't causing the noise...still there. It seems to be coming from the passenger side bank, of course, but hard to tell exactly where, but seems higher on the engine, rather than lower.

Anyone care to speculate on the possible causes? Or ideas for what to look at?

 

~Blown exhaust manifold gasket

~stripped out sparkplug threads on one cylinder

~blown sparkplug (metal part intact and still threaded into cylinder head, porcelain part blown out).

 

Thanks Paul, a good list. I was hoping for the exhaust manifold problem..but it turned out to be the #3 plug blown out.

The threads were only slightly damaged, so I gently put in another plug. Removed and replaced a couple of times, and seemed OK, however I'm not putting any money on it staying in very long. I guess I'll be checking all the plugs, and that one in particular, a little more often.

So far, I'm only in it for the cost of the plug and COP.