Newbie Here - Leaking Fuel Injectors/Knock
 

Hello everyone! - wondering if you could take the time to help a newbie. I'm in love with these old Mercedes and just bought my first one. 1979 300D. I'm excited, but I'm hoping I didn't just make a huge mistake in the one I got.

I'm an aspiring backyard mechanic; have worked on old Volvos but not familiar with diesels. I have a knocking noise that I didn't identify when I bought it. I'm also getting fuel leaks onto the cylinder out of the injectors. I just ordered the diesel purge kit and hope to find I just have an injector issue, but was hoping to see if you had any other ideas besides that. What's the gameplan if the purge makes no difference and it's internal?

Any other recommendations you have for someone who is new to the game would be appreciated as well. Thanks!

First....Don't order anything of diesel giant nor msource....they have great how to's but the stuff can be had cheaper here or on other sites...

You can use seafoam from your local autozoo in place of the diesel purge..

The leak on the injectors is probably from the injector return lines.

If you can get us a video of the knock....it will help with identifying it.

Does the knock occur only when cold? when warm?

Does it smooth out with a little more pedal?

Things to consider before the injectors:
Glow Plugs
Valve Adjustment

Gotcha, very helpful. I'll pick up some seafoam and run that tomorrow.

I tried to get a video with my phone but it came out awful. But, I found an MSource video that sounds exactly the same to me. Increases with RPM's.

Mercedes W123 300TD Turbo Diesel Wagon Restoration Part 3: Diagnosing Engine Knock - YouTube

My concern is raised because in this video, the guy finds the issue to not be a fuel injector. My understanding is knocks of all kinds can be fairly analagous in sound though?

I will get a good audio recording up tomorrow as a reference. I feel like any description I try to make may be inaccurate....don't want to throw off any diagnosis. Knock may tone down once warmed, but I'll have to confirm that. It may just be it's not as loud over a revved engine.

But yeah, glow plugs and valve adjustments are likely in need of attention. Glow plugs are taking a while to warm.

Before you start ordering things it is a good idea to try to find out what is wrong.

No amount of diesel purging is going to cure leaking Injectors. And, depending on where the Injector is leaking that can cause knocking.

The most common source of Injector Leaks is those small diameter Rubber Fuel Rturn Hoses. Remove the Old Hoses and inspect the little Hose Nipples for knicks or scratches. If they look good replace the Fuel Return Hoses and see if it solves your leak.
Look in the DIY Links for sources and types of suitable Fuel Return Hose.

Other places the Injector can leak are between the upper and lower Body of the Injector. The caues are either a poor lapping job done to the parts inside of the Injector (or dirt got in when someone had the Injector apart), a hairline crack on the lower half of the Injector or the little Fuel Return Nipples leaking where they are crimped over on the upper Injector Body.

Knocking can be caused by Air leaks in the Fuel Supply System. It is cheap to replace the 2 sections of Fuel Inlet Hose with 5/16" ID Hose from the Auto Part Store as that Hose is also rated for Diesel Fuel.

That makes sense. Thanks for the reply. I'm going to replace those fuel and injector lines then as well. Didn't see anything in the DIY for the Fuel Return hose - is it 1/8" ID?

lots of times you can make a fresh cut on the return hoses and stop a leak.I order mine from mercedes source as even here they don't have a set with end plug.I've dealt with them 10 years.True when you know your diesel better this place has good parts,for a good price

You can find the fuel return hoses at your local VW dealership's parts dept. Take a sample with you.

I ordered mine from McMaster-Carr. 84 cents/foot.

Fuel and Lubricant Yellow Tygon PVC Tubing

Tygon Formulation: F-4040-A
Very flexible
Soft (Shore A57)
Temperature Range: -35° to 165° F
Use with barbed fittings

Not only will this tubing remain flexible when used with gasoline, heating oils, cutting compounds, and coolants, it also withstands lower temperatures than other fuel and lubricant tubing. Tubing is semi-clear yellow; you can see something is in the line, but the view is limited.

5552K23
Fuel and Lubricant Yellow Tygon PVC Tubing, 1/8" ID, 1/4" OD, 1/16" Wall Thickness
Formulation: F-4040-A"

I wouldn't order the return hose from those guys - I did and had a leak within a year. Most of their stuff is sort of OK, but their business model is to cater to the relatively uninformed DIY crowd providing instructions as the value-add for the high prices. If you know what you need and get the know-how from the forums, you don't need to endure their markup.

The return hose I got was some cheap, likely Chinese stuff and was completely disintegrated in no time. Fortunately I had ordered spare hose (genuine MB from PP) and carried it in the trunk with my filters, spares and tools. Swapped them in at Vstech's place last year and all is well.

Audio Sample + Pictures
 

Alright, so a good video camera I do not have. But I pulled my condenser mic outside and got a damn good audio recording. haha.

Mercedes 300D Engine Knock - YouTube

The knock is very clear in it. It seems to go away with increased throttle. It's been colder here and been taking full throttle to get the car started. Also, want to note that I'm continuing to get white smoke at idle.

http://i549.photobucket.com/albums/i...H/P1010427.jpg
http://i549.photobucket.com/albums/i...H/P1010429.jpg
http://i549.photobucket.com/albums/i...H/P1010428.jpg

It has to be Fuel Hose. Vacuum Hose lasted me a little more than on week.
There should be more threads with Alternate places and types of Hose.
Where to buy fuel return hose VW RAbbit
http://www.peachparts.com/shopforum/showthread.php?t=238219&highlight=Rabbit
The Thread with the part numbers
http://www.peachparts.com/shopforum/showthread.php?t=210922&highlight=return+line+part+number

More Notes: Authousaz has this info next to the Fuel Return Line: Fuel Hose/Line; 3.2mm ID x 1.9mm;
According to this site: Convert inches to mm - Conversion of Measurement Units
1/8"= 0.125"=3.175mm
So 1/8" ID Hose is actually a little tighter than the 3.5mm stock Hose.

I would contact the member in this thread to have your injectors rebuilt..

http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/338033-fs-brand-new-injector-nozzles-injector-service.html

It seems like the noise disappears as you rev it....I would do a valve adjustment, rebuild injectors, new filters line, primer pump and I would upgrade to pencil glow plugs..

Possible the revs over power the knock sound.

Replace all fuel lines, that rubber line is suspicious, does it still leak?