Nailing

[wagonpilot]

I've heard of folks talking about injectors "nailing".

What exactly is this? Early ignition? A noise from the injector itself? What?

Thanks

WAGONPILOT

Sounds like a Gnome inside your engine banging a ball peen hammer against the block. Someone may correct on this, but the cause is more or less similar to predetonation in a gasser. The spray pattern from the injector, or some other part of the combustion process gets out of sorts. The rackect can go to extremes and will cause damages if not taken care of.
Most diesels have light nailing sounds at idle. When that becomes a problem is usually easy to hear.

[psfred]

The more correct term is injector knock. Usually caused by incorrect fuel injection, so that the fuel ignites late and all at once rather than burning more or less smoothly during injection.

The term "nailing" has become popular lately -- a bad case of injector knock sounds very much like someone driving a barn nail into a 2" oak plank with a 16 oz hammer.

Unless it is caused by something like sidways injector spray or junk in the prechamber, it won't usually hurt the engine. Some clatter is normal in older engines, much less so in later ones.

Causes are low compression, late injection timing, bad nozzles (sticking open, bad spray pattern, sticking closed and opening late), plugged holes in the prechambers, broken ball pins, and burned prechambers. Leaking pressure valve seals in the IP will also cause a loud injector knock.

New injectors won't fix a knock from any other cause than a bad injector.

Peter