barry i did the soak last night till 7pm today and there was a lot of black crap in there, im doing another soak tonight till thursday will see how it goes

I am not always clear. One possibility is junk has built up on the delivery valve or it's seat on the number four element that feeds the number four hard line. As the elements piston rises compressing the diesel fuel. As soon as the remaining residual pressure in the hard line is exceeded. The valve is pushed off it's seat.

This continues as long as the pressure from the element piston is greater than what is in the line. Actually what really happens the injector preset opening pressure is reached when this is occuring as well. That is when the pressure has risen high enough. So the injector dumps fuel in as long as the increased pressure is greater than the threshhold setting of the injector.

This is known as the pop pressure of the injector. Now if the delivery valve is not sealing correctly as the pressure grows less the residual pressure in the hard line goes back in past the delivery valve. Then when the piston in the injection pump starts upward again it has to try to make up the missing pressure in the hard line and also still increase it enough to open the injector. It cannot manage this so you have low output pressure. Another way to look at it is instead of the fuel going one way it is kind of going back and forth as the element piston rises and falls.

This is one senario and why I mentioned the engine should be cranked a bit to get some solvent up into the delivery valve area. The other senario is the enterance where the element takes in fuel to compress might have a lot of gunk in the area. If this were so the fuel can not get into the element or enough of it cannot. So you have less pressure and reduced volume from that line.

There are some cases where a combination of grunge and inadaquate fuel pressure may interact to deny good fuelling to an element. Actually too low an injection pump fuel pressure feed can and does affect this area all alone.

Thats why if after the cleanout if things have not returned to normal the pressure in the base of the pump will have to be examined by simple tests to make sure there is some.

Fortunatly this pump saw vegatable oil. If it had not there would be far less chance this simple approach might fix it. Also if it is not restored a careful but safe examination of the delivery valve will have to be done. There could actually be a chunk of something in the delivery valve or the solvent may not clean the valve seat well enough.

There remains a chance still the bore or piston in that number four is damaged in some way as well of course. But every other possibility has to be eliminated first. Actually it is not that much work really to do that. If you are using gas as the soaking agent remember it may be slow acting.

So your additional two day soak is a good ideal. Laquer thinner by contrast does not fool around in comparison. It disolves most grunge very fast. You just have to watch where you use it and how. It has been my favorite solvent for years for many things. Cheap in five gallon pails as well.

I took your advice and use the lacquer thiner. Also what came mostly looked like veggie oil

I am almost certain the laquer thinner will dissolve whatever is in there. It does not hurt anything else in the pump.

Because it is so much more active than gasoline you can shorten your soak period in my opinion. Up to now is far better that more than a week of gasoline soakings.

You should be able to flush it now with the diesel fuel. Then leaving all your hardlines unscrewed at the injectors. Crank the injection pump till new fuel comes out the lines. . The fuel coming out the open ends of the hardlines should flush anything that loosened up around the delivery valves out rather than trying to push any garbage through your injectors.

Then it's time for the acid test. Was something obstructing the number four elements function removed? Hooking up all the hard lines and starting the engine will tell. Hope it worked. If not then the instructions for inspecting the number four delivery valve in the archives is next.

Laquer thinner will clear a gummed up carborator for example in twenty to fourty minutes on average. This sometimes has enabled me to clean out carbs while still on the cars. Saves a fortune in carb kits and time. Carbs of course do not have vegatable oil residues and animal fat. Dried gas varnish in carborators is tough though.

Fresh gasoline will take forever if it works at all. Technically laquer thinner could dry out seals. It never has for me so far. I can easily imagine what was expelled from the injection pump using the laquer thinner. Dissolved animal fats could easily resemble vegatable oil. Any actual vegatable oil remains would have been long gone with some previous use of fuel oil by now. It would have mixed with the fuel and burnt.

ok i put everything back together today and i still have a miss, but its not as bad as before, also i opened the line on the fourth injector line and there was enough pressure in it that the fuel shoots out the top. my question to you is do you think i need to do another soak? when i did the last soak the fluid was dirty that came out. thank you again for all the help

If you feel there was a real improvement since before the soak then you have nothing to lose in my opinion. Actually it shows there might still be some chance. Had there been no change I would have seriously doubted another soak even had any chance. If dirt was still coming out with the second soak there may still be some stuff in there to dissolve.

There is no way the thinner could have improved the bore itself so something has been cleaned or partially cleaned. For the sake of continuity I know you still have a miss. Back off the number four hardline to make sure it is the same miss before filling with thinner. It is also impossible to know exactly what was in that injection pump.

Again rotate that engine to get some thinner up into the delivery valves again. Then a few hours later rotate the engine again to supply more active fresher thinner to the area again. This time make sure thinner is errupting out of the hard lines and not just fuel oil. Also again take precautions like disabling the glow circuit. The thinner is flamable.

You may as well close the return line after the first miss test before filling the pump with thinner. Then do the miss test again. This should raise the pressure inside the pump. Doing this will not hurt your lift pump or injection pump in any fashion. You want to know if the idle is improved with the return line blocked. We do not want to land up fixated on only one thing. The rough idle can be a combination of factors.



If you feel there has been a real increase of expelled fuel volume compared to what existed before. Something has changed. More volume does not indicate that under pressure the element and delivery valve can deliver a high enough pressure to open the injector.

You can start checking out exactly how to remove the delivery valve to inspect it in the correct fashion. While the pump resoaks. If the miss is there after the next soak it will have to be examined for junk or a bad return spring.

Then the number four injector checked either by changing it's position with another injector or having it pop tested. This eliminates the possibility it is plugged up with junk.




If there were not some issue with the contamination there would have been no change. Unfortunatly there is no easy solution to some of the junk getting to the injectors. In a well dissolved form it is not an issue.
as we go along it is concievable that you will be also filling the injectors and soaking them on the engine. Depends on how other things go first.


I have also wondered if thirty year old injection pumps and injectors might benifit from a cleaning for quite some time now. My current feeling is no unless there is some indication it is needed. That leads to a determination that many are not able to do yet.

For the lighter components out of the diesel fuel over the years may still respond best to the lube moly approach. This could change depending how your situation works out.

If there were a lot of garbage in that injection pump it is almost certain that some may have migrated to the injectors even before the flush. So some careful checking may be needed. Thats why I suggested checking if the miss was still on number four principally before a resoak. It does really sound like it may be coming back on line.

I know this is all tedious but you are learning in an area that has not had a lot of investigation really by us. I remember not that long ago people considered the injection pump a black box. I doubt if a thread like this would even be tried only a year or so ago. What many percievd as a trashed injection pump on vegatable oil use may not be valid on some of them. Instead just so trashed up it looks like the element bores are toast. Some will be destroyed of course.
Now just because a vegatable use injection pump does not function properly does not mean it is shot. You hopefully will be the first to prove that in a fashion we may be able to deal with. Other than the poster that soaked his injection pump with gasoline.

Hey I soaked the pump again and it's running better but it still has a little miss. But I have another problem I have an exhaust leak, when I'm driving down the highway it's really bad and Ive tried to see where it's coming from when I have the hood up and the air cleaner off. Do you have any suggestions?

Not always but usually you can feel the air movement from the source. There is no gasket used between the exhaust manifold and header pipe either on these cars. Or at least the natural aspired ones I have dealt with.

I just went back and checked. you have a turbo model. Somewhat more restricted so a length of garden hose held to your ear while moving the other end to different locations should locate it fairly easily if it is not obvious. I think the down pipe likes to fail on these.

If you have not already checked your valves for enough clearance it is time. You just might have had several reasons for your problems.. You do not have to actually adjust them but just do a quick check with feeler gauges. Any that have no clearance with the engine cold will give you a problem of some sort. Some of these cars have not been checked for years. Mercedes recomends an interval of every fifteen thousand miles.

Glad you posted again.

THank you I will try that

Awesome write up on how to clean your injection pump. Very cool this worked for you mulchman. Great info. Thanks.

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Yeah it got alot of crap out of my pump

Barry I still have a miss is there anything else I can try? When I rev up the engine there are a lot of air bubbles in the 1st fuel filter, also my primer pump has fuel in the middle of it and it never goes away. Thank you again for all your help

While it's possible that the problem is in the IP, it wouldn't be the first place I'd check. The first place I'd check is your hand primer pump. Those leak, and they're 25 years old so the deserve to leak. I had one on one of the 3 - 617's I owned that had a leaky primer pump. It would mis-fire consistently. The reason being that it is drawing in air.

A very common Diesel diagnostic is to put a piece clear tubing (5/16" line from plumbing in the hardware store) as the fuel return from the filter to the line near the driver's wheel well that goes back to the tank (the line you want to replace with clear tubing is the Cigar Hose-puffy looking weird fuel line). Watch the clear tubing for bubbles. You should have close to none returning to the tank.

But that aside, if you have a wet looking primer pump, there's a very good chance you have a leak and are getting air pumped to your IP. The air has to go somewhere. It will go to the highest place of wherever it's pumped to. Which in the case of a mis-fire is usually at the upper end of the injection pump. That means some cylinders get fuel and some get a weak injection with mostly air.

Anyways, that's what you need to check first. Clear fuel return line. And fix your primer pump. I put an o-ring around the pump handle and tightened it back down. But the right fix is to just get a new one. They're like $25 if I recall.

And I also like lacquer thinner as a solvent. But... it eats up just about any rubber or synthetic seal you can find. If you look at tables for o-rings you'll see that most o-rings used in Diesels (Buna-N and even Viton) will not withstand Acetone which is in Lacquer Thinner. So be careful. Don't use Lacquer Thinner as a solvent for everything. As Barry mentioned, I don't think you have anything to worry about in the 617's pump. But to others out there... lacquer thinner is a great solvent, but be careful. Another note, solvents will soften crud and sticky materials that have dried. BUT... usually a physical disturbance is required to actually remove the clog. This involves taking things apart and using a tooth brush with some flushing of the area. But back to the air in the lines... Check. Check. Double Check. Get clear tubing and fix your primer pump. Even if there's no air in the return line which I really doubt you should still change the primer pump. I'd bet you've got air in the IP.

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Tom's Imports of Columbia MO Ruined the IP in changing leaky delivery valve O-Rings - Refused to stand behind his work. Mid-MO MB drivers-AVOID Tom's.

Ok I will do it and back to you

To eliminate the primer pump as an intake source of air. Take a balloon and stretch it over the handle onto the barrell. Squeeze as much air out as you can. Naturally if the bubbles stop it is the primer pump. Give it enough time to evacuate any remaining air trapped in the ballon first of course.

There definatly should not be a stream of air bubbles going up through the primary fuel filter.