W115 Injection Pump Leak

[cj.surr]

I just bought this '72 220D last week and have been trying to get it running smoothly. It idles rough and has extremely low power (can't get up my driveway without stalling).

It had been sitting for a year or two, so I drained and cleaned out the fuel system, new rubber hoses, new filters. Put in a 1/4 tank of fresh diesel. Also, I did an engine oil change and I cleaned the oil bath filter and refilled it with oil.

I bled the fuel system the best I could, and it has idled slightly better since the tuneup. But it's idled maybe 20 mins combined and it still idles rough, doesn't have much power, and stalls sometimes.

I noticed that there is a leak coming from the injection pump (I did change it's lubricating oil). It leaks about 1 drop per second, and it falls onto the drain bolt. It feels like there is a bad rubber gasket where the leak appears to be coming from.

I noticed that there are air bubbles that travel up towards the fuel filter housing when priming. That hose is colored green. The spot of the leak is blue, and it falls onto the bolt (red arrow).


(The injection pump pictured is not mine, just one found on google. My primer is different, it is a black button.)

The leak appears to be diesel, but I guess it could be oil too, since I just refilled it. I have a hard time telling the difference. If that is indeed fuel, is it possible that air is sneaking in there and causing the engine to run rough?

Sorry, I'm not too knowledgeable with diesels. Thanks for any help in advance.

-CJ

[Stretch]

The red thing on this early type of injector pump (IP) is an air filter.

See if you can unscrew it and give it a clean.

This type of IP has its own separate oil supply from the engine - you need to keep that topped up at the correct level. Have you checked it?

Do you have an owner's hand book - it should show you how to do that in there.

[cj.surr]

Originally Posted by Army

The red thing on this early type of injector pump (IP) is an air filter.

See if you can unscrew it and give it a clean.

This type of IP has its own separate oil supply from the engine - you need to keep that topped up at the correct level. Have you checked it?

Do you have an owner's hand book - it should show you how to do that in there.

Don't have a handbook or service manual, unfortunately.

I believe I filled the injection pump correctly. I opened the drain bolt for the injection pump and no oil came out. So I filled it up from the top until it started to dribble out. I closed the drain bolt and poured in maybe 1 more cup of oil. Maybe I overfilled it?

It's not starting now, and I'm pretty sure it's due to airlock in the fuel system. I've tried bleeding the filter housing and the injection pump several times, but I can't seem to get it going.

[Diesel911]

Originally Posted by cj.surr

I just bought this '72 220D last week and have been trying to get it running smoothly. It idles rough and has extremely low power (can't get up my driveway without stalling).

It had been sitting for a year or two, so I drained and cleaned out the fuel system, new rubber hoses, new filters. Put in a 1/4 tank of fresh diesel. Also, I did an engine oil change and I cleaned the oil bath filter and refilled it with oil.

I bled the fuel system the best I could, and it has idled slightly better since the tuneup. But it's idled maybe 20 mins combined and it still idles rough, doesn't have much power, and stalls sometimes.

I noticed that there is a leak coming from the injection pump (I did change it's lubricating oil). It leaks about 1 drop per second, and it falls onto the drain bolt. It feels like there is a bad rubber gasket where the leak appears to be coming from.

I noticed that there are air bubbles that travel up towards the fuel filter housing when priming. That hose is colored green. The spot of the leak is blue, and it falls onto the bolt (red arrow).


(The injection pump pictured is not mine, just one found on google. My primer is different, it is a black button.)

The leak appears to be diesel, but I guess it could be oil too, since I just refilled it. I have a hard time telling the difference. If that is indeed fuel, is it possible that air is sneaking in there and causing the engine to run rough?

Sorry, I'm not too knowledgeable with diesels. Thanks for any help in advance.

-CJ

Yes, there is a rubber gasket under the Cover Plate. The Plate looks like it is held on with 4 Screws.
The Oil is not under any sort of pressure in there so you can either replace the Gasket or carefully use some Gasket Sealant.

If you are seen Air Bubbles going out of the Fuel Supply Pump you must have an Air leak.
The Old Style Hand Primer is a common source of a Air leak but it can also be somewhere in the Fuel Inlet Hoses.

Governor Diaphragm Test
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[cj.surr]

Ok, thanks for the help.

I can see some air bubbles coming from the tank feed line and going into the first small filter. They have been becoming less frequent as I bleed. But It also seems that air is getting in at the primer. Is it easy to retrofit a new style primer?

I think I will test the primer by connecting a hose that goes straight to a container of diesel. I'll be sure that no air is going in, and check to see if air is coming out. That should give me a good idea of what's going on.

[Govert]

Originally Posted by cj.surr

I believe I filled the injection pump correctly. I opened the drain bolt for the injection pump and no oil came out. So I filled it up from the top until it started to dribble out. I closed the drain bolt and poured in maybe 1 more cup of oil. Maybe I overfilled it?

You fill the IP from the top until clean oil comes from the drain bolt (red arrow). Then close the drain bolt and don't put extra oil in. The drain bolt is also an oil level. One more cup is about double the amount of oil required. Open the drain bolt again so that the oil is at the correct level. This might also resolve your oil leak.

[Govert]

Don't forget also to bleed the IP, red arrow points to the bleed screw:

[Govert]

Originally Posted by cj.surr

My primer is different, it is a black button.

Originally Posted by cj.surr

Is it easy to retrofit a new style primer?

If your primer is a black button, it is probably the newer style primer.

Here you can see a picture of the new primer:

[cj.surr]

Ah, ok. I was confused on the procedure on topping off the oil in the injection pump. I figured since it was called a "drain bolt" that you were supposed to drain it and refill. Thanks for pointing that out, I'll correct it.

The primer looks just like mine, so I must have the new one. I tested the primer by pumping through fuel from a diesel container, and it is not letting any air in. So it must be the fuel line.

I have been bleeding from the IP and the filter housing. The problem is that air is coming in from the fuel line. My guess is that it still needs to be bleed from the original hose replacement. I never bled it correctly. Or I suppose that I might have mixed up the two hoses at one of the connections. Not likely, but possible. I think that could cause air to go into the lines from the tank. If anyone has pictures of the rubber hose connections in the fuel lines under the frame, I would greatly appreciate them.

Also, I believe my no-start is due to air in between the IP and injectors. I understand that I only have to loosen the nut, prime it, and fuel will seep out when it is bled? I'm going to try that tomorrow.

One last question: is it bad to try to start the engine when it's air locked and won't start? I saw that on a website, but it didn't make sense to me...

[Govert]

Originally Posted by cj.surr

Also, I believe my no-start is due to air in between the IP and injectors. I understand that I only have to loosen the nut, prime it, and fuel will seep out when it is bled? I'm going to try that tomorrow.

If the hard injector lines don't contain fuel, it will take 15–30 seconds to start. Some people loosen the nut until fuel comes out, but that is not necessary.

Originally Posted by cj.surr

One last question: is it bad to try to start the engine when it's air locked and won't start? I saw that on a website, but it didn't make sense to me...

Not really, you want the IP to be full of fuel so that the parts there are lubricated by means of the diesel. It wears out the starter and the battery of course.

[cj.surr]

Originally Posted by Govert

If the hard injector lines don't contain fuel, it will take 15–30 seconds to start. Some people loosen the nut until fuel comes out, but that is not necessary.



Not really, you want the IP to be full of fuel so that the parts there are lubricated by means of the diesel. It wears out the starter and the battery of course.

Ok, good to hear. So I just have to let it crank for a while and it should eventually start up.
Thanks for the help.

[Stretch]

Here's a link for the owner's hand book

SECCION MERCEDES - PIEL DE TORO - LA WEB DE LOS COCHES CLASICOS

[cj.surr]

I'll need to brush up on my spanish

[cj.surr]

Originally Posted by Govert

If the hard injector lines don't contain fuel, it will take 15–30 seconds to start. Some people loosen the nut until fuel comes out, but that is not necessary.

I realized that air was in the fuel line because the feed and return were mixed. The feed was drawing from the top nipple on the tank. I crossed the two rubber fuel hoses under the pedal area, and no more air going into the first filter.

I bled the fuel system the best I could, and there wasn't any more air as far as I could tell. You were right about the long crank time. It took about 20sec, but it did eventually start up.

It idled ok, but still seemed kind of rough. Then after 10min, it spontaneously died. I have tried multiple times to get it started since it died, but no luck. The starter is spinning fast enough, it just seems to get no fuel or something.

Should I make another thread about this problem, since the title is no longer relevant?

[cj.surr]

Took a video of it running. It stalled a few minutes after and won't start back up (might just be the starter not spinning fast enough). It sounds pretty bad when revved, I'm afraid this fix is going to be beyond my skills or budget.

1972 220d running - YouTube