Update for any other W115 owners who might be curious.

I picked up the rebuilt pump today and finally got to talk to the guy that runs the shop. He seems very knowledgeable and I had a good talk with him about my other diesel.

The pump looks very good, they completely rebuilt everything, and it’s at my local guy being installed and timed.

The total for the rebuild was $1400 with a 1 year unlimited mileage warranty.

Just picked the car up. Slower acceleration in 3rd as opposed to the other gears, but it’s a completely different car! So smooth. Absolutely zero vibrations coming from the engine. I would recommend everyone have a rebuilt injection pump if it wasn’t so expensive.

I’ll have to get some pictures up. Almost perfect on the inside, engine is great, fuel system is now completely overhauled, as well as the a/c.

Now for the interior...

I meant almost perfect on the outside...

One day I'll get my 300sdl to run smooth, even if it takes an engine swap.

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

This the first time I have encountered someone who had the injection pump rebuilt and solved the problem!

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

There was a thread not long ago. Build up alone with use over the years on the delivery valves may be more common than we think.

It seems possible to clean up the mating surfaces ourselves. One member seems to have had good results. Basically re polishing the surfaces using window glass polishing compound as the medium. He could visually see the deposits I thought or evidence the contact surface was not uniform. His mating surfaces seemed to look normal after some effort.


My suspicion is he was not really cutting the delivery valves seat metal as much as cutting the accumulated softer deposits down. We do not have enough experience to determine if this is typical with these engines as the miles grow.

What is certain though is leaking delivery valves will have an undesirable effect on equal fuel delivery to the cylinders. The speed or rate of fuel flow through the valves is not great. When closing the pressure exerted is substantial. Any particle contamination in the fuel could easily get pressed onto the surface as a deposit. Hard to say if the important fuel filter were changed regularily would reduce this or not.

It certainly would not hurt though. I very much doubt that any chemical cleaner treatment that comes in a can. Would have much effect at cleaning the surfaces.

Basically if an engine is not running well. When you have eliminated the common causes. An inspection of these delivery valve surfaces might be in order. I have even been starting to wonder if this should be part of a really serious overall tune up on these very old cars.

There is an amount of leakage by design involved that can be tolerated. Yet at the same time there is a threshold if exceeded where it will impact the quantity of fuel injected. Plus what fuel you get will be delayed or retarded somewhat.

Now it gets interesting. Since the poster of this thread has resolved his issue.

Years ago I searched for a simple way for us to check out some primary functions of the injection pumps. They were considered pretty much black boxes in those days. His problem seems to have inspired me.

An old injector line with a tee brazed in it for a pressure gauge. Plus an old injector perhaps shimmed to increase the pop off pressure a little. As long as it does not drip. Ten cut off spray pattern etc does not matter. By installing this on one injection pump elements one at a time. Several things can be easily established. Things like the pressure is being generated that indicates the injectors at the normal bar rating are goind to work well. State of the delivery valve and there will be a bleed down rate of pressure noticed. On a really good delivery valve this may be very slow. Or on a really bad one very fast. I believe you would just have someone crank the engine for only a few revolutions and watch the gauge. Then stop the cranking and again observe the gauge.

Just having the injector firing into a visable container with a vent line from the container to outside air. You do not want a lot of atomized diesel fuel in the air when you are checking.

Users would quickly establish norms from abnormal. I think especially the integrity of the delivery valves . I really started to think about this area when the poster stated the car had no power at the bottom end but was not bad on the highway. I think the malfunction of leaky delivery valves is more pronounced at lower Rpms. Weak elements may also produce a similar effect.

Anyways when testing if the pressure leak down was too fast or the injector did not really pop well. Remember the test injector requires a little more pressure than the normal injector in our set up. You would have a solid reason to lap the delivery valve and test again.

Actually the state of the element does not indicate the leak back rate. It is the delivery valve only that would do that. Of course do the test a few times with each element. The beauty of a test device like this is there just are not that many variables entering the picture. You just bleed any air out of the test setup for each element under test and that is about it. In fact by intentionally disabling the delivery valve. In certain cases this simple test gear might be used to check the elements themselves.

I would expect in practice a good delivery valve would tend to actually hold the pressure just below the shut off point of the injector. The back pressure in service is really high to aid in a complete sealing of it. One reason rebuilds of these inline injection pumps are so high. Every pump probably gets a new set of delivery valves.

They are not cheap but the majority in service can probably easily be restored by lapping. Now if you see a flow erosion channel across a face or some other serious defect. Just get a better example to relap from an old pump or perhaps another member. The beauty is your test setup can verify you have now restored a good seal. There may be a very minor addition to this test if ever done. Not sure yet if really needed.

What do some of you members think?