On the way home from work today my 98 Exp w/5.4L (and 90k) started making a loud banging noise, 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?

 

Tore it open this morning....plug #3, blown out, coil pack shot.