Was your spring still the right length? How much tweaking did it get? Post information for everyones benifit. I know because of other items you did not much can be said about any contribution it made. Thats if any change was made or required.

Wait, this part can be adjusted another way without stretching the spring?

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

Not to my knowledge. The spring controlls the amount of pressure required to push a ball out of the way so fuel can flow. The spring sets the opening pressure depending on it's length.

The poster that got your attention did other changes as well. So I was just wondering if he found his spring the proper length initially by measuring it or decided to tweek it a little either to restore it to proper length or pick up a little by going slightly longer. I have just stared to keep score. So far one gentleman found his spring to be the right length upon inspection.

A shim can be added at the base of the spring, the same way injector pop pressure is set.

Thanks for the correction to my thoughts. I really should have thought about the ideal of using a shim as well. I wonder if there are any dividends to actually see what the pressure is. Apparently mercedes made allowances for up to 19 pounds residual pressure with no need to consider not using the drip method for initial timing.

Plus they thought the pump would not overadvance into problem areas. They had to consider that. Effective advance is going to be greater or should be at 19 pounds residual pressure release than 14-15. How much more would take some effort to establish. Should be considered safe at this point I think. It is within their guidelines.

This is starting to get down right interesting as people report on site.

So far so good with my 82 300sd starts great but always did better power and i seemed to have gained a few MPG

Wow, my spring only measured 13/16" or about 20.6mm I added a shim bringing the total to 22.5mm. I would have stretched it to 26, but I had forgotten the specs. Anyway, no change in power, but definitely significantly QUIETER IDLE. If I have time I will try to measure the pressure.

__________________
For Sale: 1982 MB 300TD
1995 Chevrolet Suburban 6.5TD

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel

Wow! Now that is interesting. Pull it out again, and adjust it to spec!

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

The reasons.....

I asked if it started harder just in case you had your effective timing too far ahead by really over stretching the spring.. It would really benefit you and us to get a pretty exact handle on how many miles per gallon you have gained and what you are getting now If possible.
When I mention effective timing I mean the timing of the injection pump when the engine is running. It is probably the same as the drip timing point when the pressure in the pump is at about 14 pounds. At lower pressures it is retarded. Any pumps where the spring has aged a little will have less actual pressure. At higher than the 14 lb pressure advanced timing over the drip position does take place. Increasing lockstep with the pressure rise. This is basically caused by the elements in the fuel pump loading a little more fuel at the higher pressure.

With more fuel in the elements they come up to the opening pressure of the injector earlier.. It is advancing the pump the same as if you got out of the car and manipulated the pump physically. It would be good enough if this was the only effect

Mercede benz engineers seemed happy if the pressure is not higher than 19 psi in the pump. It is their upper tollerance. So you could describe 19 pounds as the edge of safety with what is known. Again just in my opinion. Few if any of our cars are now at 19 psi. Any higher is at your own risk and right now I would not go there if ever.

What is pretty certain is if the residual pump pressure is lower than the average of 14 lbs pressure you will not get the top milage possible no matter what you do otherwise. The second component that is affected by low residual pressure. If the pressure is low it is not an equal opportunity situation when the elements load. They will intake various amounts of fuel.

Some will get enough and some not quite enough. So besides unequal firing pulses the injector opening points are going to vary in time. Each will hit its effective injector opening pressure at slightly different times in relation to the designed interval or sequence. So your milage and power further deteriorate. Now this is hard to prove. Yet is the only realistic explanation I can find for all those posts where people stated they changed their fuel filters as a regular maintenance thing and the fuel milage went up.

This theory is also backed up by what some people have indicated when their fuel supply was problamatic. . This is clear to me anyways as effects posted where not logical otherwise.

I was so close to this area and generally frustrated awhile ago. I had decided the only function that residual fuel pressure performed in the injection pump was to provide a constant fuel supply for the elements to load.

Fuel was cheap when these specifications where writen. There is the possibility the cars and springs were much newer and none if any had sagged. This one I think may be it. Only in the last few years has this become an increasing problem of signifigance because of aging.

Fast forward to today where we want every last mpg we can get. If Joes 240d is getting a solid thirty miles per gallon on the highway I am not satisfied with my 24 mpg. I want the thirty the design is capable of. So I come out of the woodwork and want to know why this discrepancy exists. At first It appears it might be a combination of many things since these cars are old. Slowly it becomes pretty evident the spread is getting some pretty fixed values. This brings out the suspicion it is a common denominator.

I look and look and cannot find it. It is a simple engine yet I cannot find it. There are clues that seem to defy logic. They are consistant enough to believe. Why do the 617 engines not seem as badly impacted for example?
They are basically identical to the 616. I just cannot locate that common denominator. I know I can be stubborn with problems so I am not concerned. Someone will post something one day that ties all the unknowns together.

Cervan did this. He stretched the residual injection pump relief valve spring and power came up. Instantly I knew the elements in the fuel pump did not totally self load. Instantly I knew the timing was impacted. Almost instantly I also knew this was the most likely long elusive source of the missing milage as well. This was so because all the illogical seeming side effects I had observed over time now rationalise out. If Cervan had not stretched that spring or someone else did not either I think this area would have remained invisible. We just would have continued to live with the negative effects.

His post immediatly indicated to me this residual pressure was swinging the injection pumps timing and answered why people reported better milage with fresh filters. There were other less important posts that where a major contribution as I went along.

I thought it might have originally been found with the milli volt method if I had been determined enough. Sam and Yellit made great efforts to try to make it work. Then I realised just how stubborn those injector lines where by following what Sam and Yellit where attempting.

The question of dynamic spread checking the pump by this method was dead. The pizzo method would hit the same exact thing. Or if the pump manipulation was as easy as volkswagons is. I would have picked up the dynamic or running timing was all over the place on these pumps compared to the drip setting. The majority would have been retarded if the milage was substandard. Thats providing of course other engine items where in reasonable condition.

Now the important part. The potential financial savings unless your car is at the top end of the milage profile for it's type. In an average week or two of part time driving you will save enough money in fuel consumption to pay for a gauge that you aquire to get that residual pressure set right. It will take a pressure gauge to get it right. The recommended spring length just puts you in about the 14lb area maybe. That is a very weak maybe. You should read the pressure and tailor the spring to 19 psi. Either stretch or shim it. The shim preserves the spring for other adjustments. One of our members clued me in that the spring could be shimmed instead of stretched preserving its found length. Shims may allow critical minor adjustment as well. Stretching may be too coarse an adjustment.

If you leave the gauge installed just before the pump or on it you will see when you should change fuel filters out. The presure will just start to fall. It allows you to try different pressure points as well for maybe a smooth spot. For example you might get about the same milage at 17 lbs pressure as you do at 19 lbs pressure but the engine is smoother at 17 lbs. For certain troubleshooting that gauge in place can even make it easier if it occurs.

Back to the poster I am responding to.

I think about 29 mpg on the highway is the ceiling in general for your type car. I may be wrong. Thats before loading winter fuel drops your milage. . If the effective timing gets too far ahead in my opinion power will be high but milage will fall off. After considerable thought the residual fuel pressure in the injection pump should be adjusted to 19 lbs. There may be recomendations for possible still further advances later on depending on a lot of knowledge being gathered and evaluated.

This 19 psi again was allowed by mercedes. Will give the best combination of power and milage safely that I can think of at this point. No chance of direct resulting engine damage. You might even be around that pressure now for all I know. Find out yourself where you are. It might be important. Look at it as a part of the required cost for better performance and better mpg. Very,very cheap price to pay. Long post but covers most things the average guy should consider in my opinion.

Remember this is really a major breakthrough in understanding on these cars and not run of the mill stuff. Some may not understand the implications yet but many will.

The initial changes are. Do not drip time your engine if you do not know the residual pressure in you pump while the engine is running. You will not know if the engine has simular running timing to the drip timing. If the pump pressure is really low the engine will run well retarded from the drip setting intention. .

If you randomly decide to elevate the residual pressure to well above 19 pounds you may hammer your engine to death with pre ignition forces. Filters are important to good fuel milage. Check the pressure, permanently install a meter or change them on a regular basis. It is no longer sensible to keep them in service till they partially obstruct.

You will spend a lot more in decreased fuel milage than filters cost. Amount unknown but could be substantial depending on variables. What people have reported over time is now proven. Free flowing fuel filters increase milage to a noticeable extent. We now know why.

Slight advance in timing would have occured as well. The increase in timing would not smooth the idle in my opinion. No power gain noticeable because when I say a timing advance it is from a really retarded position if the engine has been drip timed. You have moved up a little towards the drip refference timing but still have retarded timing. As you approach 14 psi the timing will start to match the pumps drip timing better. At 15-19 pounds the timing advance will be a little past the drip position but safe.

On an indirect diesel the best indicator of when you are at the point of matching your drip position is the throttle pickup from idle should be crisper when manipulating the linkage under the hood. This somewhat depends on all the other engines components condition. Yet without doing what you are doing now the end result of anything else could not be satisfactory in my opinion.

There is no reason not to move the spring up to the 26-27 mm level. Shim it up if you want to temporarily see but the changes in your car should be signifigant.

I have almost decided that a pressure monitoring is going to not only be recommended but jumped on. There is so much to safely gain. Think good miles per gallon gain and power for the price of installing a pressure gauge on the pump or input to the pump. It's real.

Also think 19 lbs pressure or slightly lower. I think you may have just hit about 11-12 psi. Just a guess. What happened in your case? The injectors are all opening sequentially correct now as the elements tend to fill with more equality is a real possibility. Plus all injectors spray a more balanced quantity of fuel. So the engine is simply more balanced in firing. This is the second component that effects milage. My guess you have just improved yours some what but not as much as possible.

Also thanks for having enough interest to try. What you initial guys report back is going to cause a stampede I think. Just think about it at the extreme some 240d cars will gain 6 mpg for less than fifteen dollars or less perhaps. My estimated cost of a gauge and fitting if you know where to shop. The additional power no charge. Maybe yet another kit someone should make up.

The two spares I got from the junkyard yesterday had the same length, 20.75mm and 20mm. The first was from a 75 300D and the second was from an 81 300D.

I'll get the pressure gauge installed this weekend and see what happens.

Are you wondering like I am if the pump builder used different length springs over the years? If not there is some really serious settling of springs out there. Of course your pressure gauge readings will answer the question.. Basically the same pump over the years with the same requirements though so I suspect settling...Still good to know for sure.

Allready the relief valve phantoms strike the junkyards? I can see the posts now. Anyone know where there is a junk diesel mercedes that still has it's relief valve.

A quick test with my air regulator shows a 14psi crack pressure with a 20mm spring and 30psi with a 27mm spring. It might be different with fuel instead of air but I definately won't be trying 27mm right off the bat. I'll get a bunch of crush washers and try 1mm increments until I get 19-20psi on my pump.

Unfortunatly thats pretty conclusive to me. We will be dealing with different spring lengths I think. All pumps might have to be checked with pressure gauge before doing anything. I though the freehand stretch was not accurate enough without a gauge check anyways. Just too hard that way to get to wherever it is finally decided produces the best results . The second issue was if the car already gets decent milage the calibration is not that far off. It may still benifit somewhat from fine tunning.

Well a little update, the reason my car was so hard to start was because the no 4 glowplug was bad (allthough it passed the ohms test with 6 ohms resistance) Now i found my spring that flew out of my hands, it got a little smooshed because i stepped on it (or ran it over) but its now stretched to 27mm and im going to see how the engine runs with that installed. I also have retarded the timing as far as possible (a little bit more than i had it set at before i thought i had it set as far as possible before but it wasnt) So ill report back when i have it all together.

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Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?

As long as they would add one additional commandment for you to keep thy religion to thyself.
George Carlin (Wonder where he is now..)

1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.