If the fuel is running down out of the IP, check the fuel return line on the side. There should be a restriction or a spring loaded valve in there to hold pressure in the IP. It is the thread as the inlet, and I've heard of them being swapped. That would account for injector noise, as the amount of fuel being injected could vary somewhat at idle.

There are a number of causes of injector knock, not the least of which is being a diesel engine. You will always have some diesel noise (least on the TDI or CDI engines). A hard "snap" rather than a rattle is an indication of a problem.

Injectors can be taken apart and reassembled without pressure testing, but I don't recommend it. Too much chance of more trouble than you started with. If you want to have them tested, pull them and take them to a diesel shop, they will test them for free. The opening pressure is set with internal shims, so you must have a test bench.

A broken ball pin in the prechamber, bits of burned out glowplug tips, and incorrect IP timing will all cause the same symptoms as a bad injector. So will a bad chain tensioner, as chain slap sounds a lot like injector knock. Low compression also caused injector knock. You will have the other symtpoms of low compression if this is the case, though.

You can test for a bad injector by sequentially loosening the injector cap nuts while idling -- each cylinder should give the same amount of idle speed reduction and increase in vibration. If the knock goes away when you loosen a cap nut, that injector is bad. Ditto if the idle doesn't change as much for that cylinder as for the others.

One last thing to check is for good seals at the pressure valve holders. Leaking seals will allow fuel to leak back in the injection lines, causing all sorts of noise and running problems. Seals are easy to replace. This was the case with my 87 and gave the following symptoms: serious knock on #4, poor performance until the turbo kicked in, some knock on #2 and #3, all of which dissapeared on loosening the cap nut. Rough idle at all temps, but no starting problems. No smoke, at low or high speeds. Slightly low compression on #4.

Turned out that someone had been in the pump, and failed to properly torque the pressure valve holders. New seals fixed everything.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!