Diesel Knock

[mjrose]

I'm getting a fair bit of diesel knock on my 95 w124 e300 diesel (NA om606 engine) between 1600 and 2300 revs. The noise is most noticable on diesel and quietens when running on veg.

I'm guessing the injectors are on the way out or perhaps timing chain stretch has knocked the injector pump out. Does anyone have any ideas what this is likely to be?

The car has done 137k.

 

[SilverSaloon]

you could try running some injector cleaner through the tank.

 

[mjrose]

Hmm i've tried a full bottle of that (8 tanks). It didnt seem to make much difference to the knock, but did seem to increase mpg a little...

 

[Number_Cruncher]

Leave the injector pump well alone.

Take your injectors out, and have them tested for;

opening pressure
spray pattern
leakage

If you're going to run on DIY fuel, you'll probably be better off obtaining or making an injector tester - you'll be needing it again soon enough!

 

[spock500]

try Keith at United Diesel, very reasonable with first class service

http://www.uniteddiesel.co.uk/contact-united-diesel.php

<one came to £150 to fully recon only 5 though

 

[Dieselman]

Connect a seperate fuel pipe to the filter feed and a return to the tank return and run half a litre of neat injector cleaner through from a bottle drawing from and returning to the bottle, then run the car on quality diesel.
The veg oil is blocking the injectors slightly which is most noticible under light load and small injector openings.

I'll be surprised if that doesn't fix it within a day.

 

[c240yaz]

Pre ignition. Basically the fuel oil is igniting too early.

Common causes are dripping injectors, allowing fuel in too early on compresion stroke (or constantly on all strokes) or fuel pump too far advanced in injecting the derv..

 

[Dieselman]

Before doing anything disconnect the EGR valve vacuum pipe and see. If the valve is sticking open it will cause symptoms like this.

 

[mjrose]

Thanks for all your replies. I think i will start with Dieselman's suggestion first, being the simplest to try.

Dieselman: The EGR system is already disconnected, buts thanks for the suggestion anyway. To clarify your injector cleaner suggestion; essentialy you run straight injector cleaner into the IP allowing it to be injected and collecting any return before it goes to the tank. I assume to do this you just need to to turn the car on the starter (as it obviously wont start on inector cleaner) allowing the IP to pull the cleaner through? Is there a brand of diesel injector cleaner you would recommend?

Spock500: I may go down this route if the cleaner is unsucessful. Just to confirm; did you say he charged £150 to recon one injector or five?

 

[Dieselman]

Loop a container of injector cleaner to the filter and return it back to the container from the tank return pipe, just as if you are replacing the tank with a seperate container of fuel.

The engine will run on injector cleaner.

Rev the engine to open the injectors more than at idle and especially rev into the trouble speed zone.