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Old 08-09-2013, 01:36 PM
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scottmcphee scottmcphee is offline
1987 w124 300D
Join Date: Mar 2008
Location: Edmonton, Canada
Posts: 1,539

Do things improve on a fully warmed engine? I couldn't see the temp gauge in your video you flashed by pretty quickly after starting. Personally I want a little nailing on a cold start, that should quieten down once warm. It's more of a timing advancement indicator for my preferences.

Nailing is worst at cold engine. Crack the injector nut on the suspect nailing injector, when things are cold, does it quieten down quite a bit? Adjust pop setting and check spray for that injector. You may as well walk through the line of injectors cracking one nut at a time and determine the contributions of each, as to the smoothness of running and sounds emitted. You're looking for uniformity. You'll need the right size crow foot socket for this job, to make it real easy. (17mm?)

If running a purge fluid (transmission fluid) on a short tube looping under the hood changes sounds dramatically and things quieten down... your timing might be too advanced. You can try adjusting (retarding) the injection timing to quieten down on diesel. Do this by tipping the IP away from the head. (check other posts how to loosen 3 nuts and the bolt at the back of the IP, then use adjuster screw to change timing, have a IP front O-ring handy and ready to put on, these crisp up and may break or leak when adjusting timing). If you then drive and have a dog, you've retarded too much: advance back and you'll get more sound, but more pull too. There's a sweet spot in this range that will be right for you and your engine's overall condition.

Any "double frequency" sounds are associated with things turning at crank speed, things that sound half as often as that are valve train related (tappets, etc.). Valve train sounds are also "lighter" sounding.

A really worn chain makes it hard to get the right sounds out of the engine, no matter how much you advance or retard timing. Check stretch, various methods documented in other threads. When the chain is newer everything is just more harmonious and less "random" relationship sounding. Hard to explain but you'll know when you hear it. Oh, and the amount of grey smoke on colder engines can tell you a bit about chain stretch too. New chain for me made all the grey smoke go away on my car at idle, even when warm. Now I just blow black (when I want to) using the pedal - an no ALDA!

If no matter what you do with an injector on a particular cylinder appears to have any effect, swapping etc, and problem stays with the cylinder... you could have low (maybe zero) compression on that pot. Let it be.

Check for exhaust leaks or cracks in gasket or manifold around a particular cylinder. These sounds can fool you into thinking something is wrong on the injector side. Nope.

Get a mechanics stethoscope, and poke around the suspect injector, comparing to neighbours. This is a cheap and easy way to find injector issues. You can hear the high pitch "ping" of the pintle reseating after each firing. If you're not too old. Again, looking for uniformity across the line of cylinders.


that's all I can think of now
Scott McPhee

1987 300D

Last edited by scottmcphee; 08-09-2013 at 02:59 PM.
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