C250 TD 1998 heavy black smoke after seal change fuel pump pressure valves

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stephen290361

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Dec 22, 2011
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C250 TD 1998
Hi all
Not sure if anyone can help I had a leak from one of the pressure valves on my fuel injector pump after spending a couple of days locating the tool to take it of changed the the rubber and copper seals on all five valves ever since then the car has been running badly and heavy black smoke has been poring out the exhaust. I have had them of and on replacing valve housings and seals every time with little or no effect. The bosch inline pump is meant to be bullet proof and I can't see how I have damaged it by doing what I have done. I have spoken to mercedes - as I have ben there several time now and they say that i can't do any damage to the pump. I have listed some of the things I have tried;

1. Change all seals torque setting to 26lbft
2. Bled pipes up to injectors while running
3. Progressively torque down valves.
4. checked all valves while running to see if they are injecting on a regular bases.


The car was running fine before I have changed the pr-filter and main fuel filter + rocker cover seal and oil filter I can't see how I have effected any other part of the car. On the second attempt I have left the inlet manifold off don't think that would make any difference to the basic running.

I would take it to the garage but can't as it is running and smoking so bad I don't think I would make to the end of the street without being stopped.

Hope someone can help and apologies for going on so much.

Steve:(
 
It sounds like it's running extremely rich, which could mean either too much fuel or not enough air.

I don't know the 250TD engine, but I'd be looking at any overall fuel adjustment that may be available, or seeing if there's any way air could be leaking out of the intake system.
 
Hi Startman

I have been trying it with the inlet manifold of just so i don't have to keep taking the thing apart every time. Would this make a big difference then?
 
if you've messed with the delivery valves themselves then they (iirc) need to be rotated correctly for correct running. When changing the delivery valve seals then its wise not to touch anything other than remove the spring and copper and rubber washers. do not touch the valve under, which it sounds like you have done.

on the US forums there are a lot of forum threads covering this.
 
Hi Silversaloon
What do you mean by (iirc)? Some people do say that removing the small cylinder a centre valve is not what you want to be doing and if you do you need to put it back the same way (but there are no markings or special grooves that I can see) and when you ask mercedes parts they say it shouldn't' matter. I have checked to see the orientation of the other small cylinders and valves and they are all different.
 
Thanks for that link reading through he took out the long cylinder under the small one i wouldn't have thought that would be a good idea.

I have spoken to some pump specialist and they contradict themselves also and they say bring the car or pump in - no good when its chucking that much smoke and reluctant to take the pump out

I think I will put it ALL back together again and see what happens.



Thanks for your qui
 
If the engine is running without the inlet manifold it seems likely that it won't be getting the turbocharged air, just air at atmospheric pressure. This would be nothing like enough and would make for very rich running. Replacing it may solve the problem, but before doing so check the link from SilverSaloon.
 
:bannana:Thanks for that but think I found the problem isolated each pressure valve and found that one of them was not working smoked stopped straight away just need to make sure if its the injector or the pressure valve on the pump so will change round injectors to check.

But thanks guys for the quick response and advice very much appreciated.
 
:bannana:Thanks for that but think I found the problem isolated each pressure valve and found that one of them was not working smoked stopped straight away just need to make sure if its the injector or the pressure valve on the pump so will change round injectors to check.

But thanks guys for the quick response and advice very much appreciated.

I was going to suggest crack each injector pipe off in turn and see if the smoke stops.

Try swapping the injectors over, it sounds like one is stuck open, possibly due to "foreign matter" entering the nozzle.
Instead of swapping them round for diagnosis, after sussing which is the "smoker" remove it from the head and then reconnect it to the pipe and run the engine, while observing the spray pattern as it sprays into a jar.

Warning: Do not allow the injector to spray onto you, it is high pressure atomised diesel oil.
 
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Hi Dieselman
I will give that a go. just trying to locate a 22mm socket to take it out.

The car has done 105K now so seeing I have the car apart maybe a good idea to change all the injectors looks like you can get a set for around £80.00. Have the washers already. Just want to know before I do remove them all what kind of issues I may face can anyone advice??
 
I'll be amazed if it needs injectors at 105k miles, add another 100-200k miles and maybe.

You need a very deep 22mm injector socket.
 
A quick way to check for an injector being stuck open is;

- run the engine
- stop it
- take the injector metal feed pipes off, but, don't clean or blow the fuel out of the injector tops
- ask an assistant to crank the engine while you watch.
- if any fuel blows back out of the injector top, it is stuck open - you should see NOTHING being blown back at all

It's very easy to damage the injector pumps when doing this repair, because there's a lapped fit between the delivery valve holder and the top of the plunger's barrel. This job really should have a health warning with it.
 
A quick way to check for an injector being stuck open is;

- run the engine
- stop it
- take the injector metal feed pipes off, but, don't clean or blow the fuel out of the injector tops
- ask an assistant to crank the engine while you watch.
- if any fuel blows back out of the injector top, it is stuck open - you should see NOTHING being blown back at all
That's a cracking method NC...
 
That's a cracking method NC...

Although it's crude, at least it's quick & cheap!

I found it on a Bedford CF diesel engine I was working on - for some reason, I cranked the engine over without the fuel pipes on, and a spray of fuel was pushed back out one injector by the compression. I removed and pop tested the injector - it didn't build any pressure at all.
 
Hi Nc

Good way to check should have read before I took injector out. Any way have made up tool to take the injector out and checked to see if it was blocked and found it was in good condition, swapped injectors only to find that the black smoke did not move with the injector so back to the pump. And MC you are right "this job should have a health warning".

I am not sure what you mean by a lapped fit between delivery valve and holder I have replaced copper washer and rubber seal 4 times and torque set to 26bft. If you have any more detail it would be appreciated as this job has be going on for more than 3 weeks now and is driving me INSANE!
 
In this thread,

http://www.mbclub.co.uk/forums/engine/55297-delivery-valve-seal-tricky.html

There's an extremely helpful post by compress ignite where the exploded diagram of the delivery valve is shown.

The lower face of part 7g is a very finely lapped flat surface, and this mates and seals with a similarly lapped flat surface on the upper edge of the pumping barrel.

This lapped seal has no O ring or gasket, but, must seal against full injection pressure.

Therefore, if you disturb part 7g at all during the process, it's likely that you will end up with a leak there.

The same goes for the fit and seal between the delivery valve, 7k, and the upper taper surface of 7g. Although this part doesn't seal against full injection pressure, it's not far off. If you have rotated the delivery valve relative to the holder, or, even worse taken them apart and got some dirt in, then, it won't be sealing, and will cause the injection process to begin and end with a dribble rather than sharply and smartly as it should - this dribbling fuel will give lots of smoke.
 
Hi NC
I have the exploded view of the delivery valve and an explanation with diagrams showing the procedure (it's from Parrot of Doom) in that he says he was told not to take 7g or 7k out but he dose take one out and has no problem. I unfortunately have taken all 5 out 4 times now and it is only valve 5 (thats if you say 1 is at the front of the engine) that seems to be the problem. I take on board what your saying but how do you fix it without having to take the pump out and send to a pump expert which is likely to be more expensive than car is worth? Or is that the only way?
 
My guess is that you used a magnet to remove parts 7g and 7k, and inadvertenty lifted and rotated the plunger barrel too.
You may well not have noticed, but perhaps felt the assembly was a little tight when screwing back together?
Basically the plunger barrel must be aligned correctly, and rotating it will set it in a position to deliver much more, or even less fuel (down to the way the pump is designed, the rack rotates the plunger, which has a spiral groove - misaligning the plunger barel will have the same effect as turning the plunger, hard to explain but NC and DM know what I am talking about).
Theoretically you cannot do this, as the plunger barrel is located with a steel pin, however it is possible to lift it, rotate it, and push it back in displacing the pin (don't ask me how I know!).
The clue will be a location pin protruding slightly further than the rest.
The pins will be visible if you remove the inspection cover along the side of the pump, if the one for cyl 5 is sticking out, remove the plunger barrel, tap it back in, align barrel and away you go.
 

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