I swapped the lines back to original configuration and gave it a drive, and it drove much better. However after I got home I had to press the stop lever on the engine due to the fact that I removed the golf tee from the rubber 3-way elbow in the engine bay (I thought my brand new check valve would solve the problem but it didn't), and left my keys in place. So the battery died, but that's happened before and I re-charged it and will be taking it for another test drive tomorrow after letting it sit. When I drove it after swapping the fuel hoses, it drove as I used to remember it. When I switched it back to original configuration, it seemed to drive normally, but I want another few miles and lots of starts and stops before I can say it feels normal or not.

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No none at all. The only thing I did in the engine bay in the last week was to swap out the fuel filter with a new one, drain some transmission fluid which was poured in excess, replace a few vacuum rubber elbows with new ones, and spray some CRC electronic connections cleaner on a few connections. That's really all that I've done. When you say conrod do you mean the ball-and-cup connections that are all over the engine bay which actuate the cruise control lever and the throttle levers? If so, haven't touched those in ages. Cruise control ball-and-cup is in tact

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I agree with you. Tomorrow I will drive it in original configuration again and know the final result. I trust your knowledge and experience

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That right there would be a mistake.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I have no arguments with anyone posting other information. They all could be right.

Since you did not hear the relief valve open to discharge. There remains a problem in the fuel supply system. That will probably totally fail you at some point. Is it the problem now? No way to tell. At the same time if left alone will ultimately totally fail I suspect at some point.

Cheap and not hard to address getting the fuel supply back to normal. I call it a fuel system tune up. Even Mercedes literature recommends a periodic checking of the system.

Still some systems have gone about forty years with only fuel filters being changed. Still operational but many are compromised in many ways. A decent percentage of roadside breakdown issues will eventually occur with these fuel supply systems not being periodically checked.

Your system is already partially diagnosed. You cannot reach relief valve opening pressure because the lift pump valves are leaking too much. Or the relief valve is open already. Simple tests can indicate what it is.

I may as well describe the tests. With the return line from the injection pump removed. The primer pump should build pressure before any fuel is discharged. If the pumping did not build resistance before the fuel was discharged the relief valve is faulty. To verify this close the relief valve output. If you can now make pressure when pumping it is the relief valve for certain.

If not the lift pump valves probably need renewal. The check valves in the lift pump are letting the pressure escape back through them. Actually they will disable any attempt to build enough pressure if leaking enough.

The other alternative test to use. Is to put a gauge on the output of the lift pump. Cranking the engine should produce at least 25 pounds of pressure. When the cranking is stopped the pressure should not drop off to nothing in an instant. Dropping slowly is acceptable but with really good valves it should hold the pressure.

Another indicator is how quickly does the engine start after siting for a day. If almost instantly at 65F degrees or above. Chances are strong that the relief valve is totally closing and the lift pump valves are in good condition. The engine did not have to crank to get enough fuel available to start as it did not drain fuel back when sitting. If it where not for your description of how the primer pump was acting. I too would have suspected fuel issues.


Multiple engine rotation startups can have many causes. One often ignored is there is just not enough fuel sprayed by the injectors. Created by lack of fuel present in the base of the injection pump so the lift pump has to resupply and build some pressure before enough fuel can be sprayed to start on. On a tight system as soon as the engine starts to rotate fuel pressure in the base of the injection pump is almost instantly increased. Fully filling the injection pump elements.

Hopefully it is true for my 300SDL.
when my brother got it, it was very dusty and was sitting outside.
even the engine bay was dusty.


so it was sitting for quite some time.

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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.

Just a comment regarding fuel degradation... Diesel actually begins to break down into polymers(that nasty tar in your tank) as soon as 90 days after refinement from crude accoriding the the petrol gurus I learned from. From refinery to transfer tank, to distribution, to fueling station, there's a whole lot of contaminants that can serve as a catalyst to speed up the break down. Furthermore, if you have build up in your tank already(most of these smokers do), it will also increase the rate of degradation. Just from the bits I gleaned, diesel can go sour in a year even if its in a clean tank. At the very least it will begin to gum up the tank, lines, and god forbid the IP which is what I've been struggling with(see saga of an IP...). I don't think a new tank screen will help if the build up in your tank looked anything like mine. I'm not sure the easiest way to get it out but I pulled the tank, filled with pea gravel, sand, and rubbing alcohol. Next I suspended it from a deck railing and see-sawed to and fro for about... a long time. I used alcohol because the tar reminded me of aviation gasket sealant which is easily removed with isoproyl. It's relatively inexpensive, readily available, and slightly less toxic than ethyl. The tank was like new in less than... a long time. It's labor intensive. I flushed the metal delivery, return, and injector lines; using the same solvent, a fuel pump, and a closed circuit. I changed all the hoses, new screen, filters, cleaned/rebuilt the fuel sender, new cap, rebuilt the lift pump, flushed the IP, and Voila! I still have problems but at least I know my fuel delivery system is not and will not be a problem for a very long time.

Gents, my car is up and running again with no fuel starvation issues. At this time there are three products in my fuel tank: 1. half a bottle of star tron; 2. a few ounces diesel kleen; 3. a few ounces of lubro moly diesel purge. I started with the few ounces of diesel kleen, swapping the fuel filter, and the pre filter.

After about 10 miles of driving on the diesel kleen in the tank, I suspect that helped loosen any debris that may have been clogging up the tank (maybe). I then did a diesel purge using lubro moly, the same way I have always done, using the diesel giant website as my guide. Surprisingly, after the diesel purge with one full bottle of lubro moly, the engine vibrates a LOT less than it previously did.

I drove it once for about 30 miles, and whereas before the purge I would get a heavy vibration in the cabin left to right, now it's noticeably smoother. After doing all these things, I then took my car to the mechanic to check out the primer pump, which as I had said was only a few years old. He pumped it for me and said that, while it was still pumping, it wasn't building up pressure like people on this thread discussed.

He said that either the pump itself had gone bad, or something inside the injection pump near the primer pump had gone bad. He told me the thing in the injection pump that could have gone bad, doesn't require fully disassembling the injection pump in order to fix, and that before trying that, it would be worth replacing the primer pump with a new one.

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240D Bill. With respect, and without prejudice, if that is the case, then how is it that I'm currently driving a car which has 1.5 year old diesel in in, plus about a quarter tank, plus a few additives mentioned, and the car is still strong and actually runs? You definitely know a lot more about diesel and these engines than I do, but the proof is in the pudding.



By the way, the method of cleaning you describe is very coarse. For the time and trouble, I would rather buy a new gas tank. But I guess if I had to do that, I would still be: a) removing a tank, and b) re-installing it. So maybe the additional work might be worth it to ensure a clean tank. Personally, I would just remove the tank, fill it with a few gallons of Evapo-Rust, and just rotate it every few days for a week. But whatever works, works

My fuel tank strainer was replaced literally almost just prior to filling the current tank of fuel, and is essentially brand new with the exception of the diesel fuel which you said would have gone bad by now, but which is making my car run. Therefore I don't see the need to remove it and do any kind of cleaning at this point. I'm sure these cars could use a full flushing of the fuel system, but to me and for my purposes, I just care that the car has good compression, drives with good power, and doesn't vibrate excessively. I drive this car like 10-20 miles a week on average, so it's not my daily driver, it's just a backup car and a fun weekend car. So I'm not about to flush and replace every fuel line especially if the car is running strong now. But we all have our own purposes for these cars

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I'm going to ask my mech to perform these tests. The primer pump only increases in pressure slightly, so whatever the lift pump is, it's probably gone bad. I'm assuming that's the part inside the injection pump that works in conjunction with the primer pump, but I could be totally wrong. After sitting for a day or three, the car cranks right up.

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Well you did good getting the mechanics opinion. I assume he has seen more than one older Mercedes diesel. Do not go back right now. I suspect the various cleaners you have added might be cleaning either the lift pump valves or the relief valve.

The part of a little concern is not an internal part of the injection pump but an easily accessed part on the outside. There is a good chance that the effort to pump the primer pump might increase with some miles.

As for the primer pump. It is not a complete pump in itself. It uses the valves in the lift pump. All it does is on the spring loaded upstroke it develops a suction. This draws fuel from the tank. When you push it down the valves In the lift pump close. Then the fuel is moved forward.

If the primer pump where bad I suspect it would leak. Unless there is a seal on the pumping shaft that connects to the piston or is the piston. itself then it would be redundant. I suspect that when you pump it you are in actuality pumping the whole piston itself. So that model too will leak fuel if defective in my opinion.

You should now wait awhile before determining if the fuel system needs service. It may self correct. You want to see it reach a point where you hear either the relief valve can be heard to unload. Or the resitance to pumping the primer pump does not increase. Over what it has been.

I am not suggesting that you did not have compromised fuel. I am suggesting that your fuel supply system was not normal earlier on. You will not hurt a thing by periodically trying the primer pump to see if the resitance is increasing. If it never does the fuel supply should see some form of attention.

As for sitting diesel fuel I respect all opinions. Fuel sold in the summer months has no additive components to thin it down. Kerosene was the optimum cold weather or winter additive In the old days. As a general rule if there was no residual water In the tank as well the fuel remained good for at least a decade.

Because the additive perhaps by many refineries has been replaced with some other viscosity reducing chemical formulation than kerosene. A concern of them would be the dollars saved over the effect of long term storage. So fuel purchased as winter fuel may have far shorter storage life.

As an example for quite a few years here regular gas went sour in a very short time. It did not prior to that. To avoid the issue then we were told to buy premium if the gas was to be on hand very long. Yet over the past couple of years the same effect is not happening nearly as fast.

So they obviously changed something yet again. In many market areas in America many members reported an absolute stink was emitting from their tailpipes. Plus there was issues even burning the stuff. The refineries are obviously experimenting from time to time.

I have 200 gallons of furnace oil on hand that will not be burnt in the furnace. It is probably five years old. I have no fear in using it fifty fifty with straight diesel fuel. The base product for diesel fuel has been there for millions if not billions of years. It will retain a reasonable long storage period unless modified to an unreasonable state. Usually by cheaper additives to save money. Even with the reasonable and non destructive types of additives A decade is not an unreasonable period to me in storage.


Assumptions that we all buy the same type of diesel fuel are simply that. An important reason not to buy diesel fuel at low volume outlets. Is they are usually supplied by independent bulk carriers.


I know they do not always clean out their tanks properly from the previous contract load of whatever was in their tank. Where the larger retailers are supplied from dedicated tankers. Or what little was left in their tanks is no issue.