Amazing. If I understand. Wide open relief valve and power is even stronger?
I await your theory. This development is interesting to say the least. I of course assume with the spring out the return valve is open all the time?

Well i have driven 50 miles so far and the gauge hasn't moved power is still really good. my timing chain is 2 weeks old and so are the filters. so my car should be a good bench mark for a 617.

The expected possible milage increase I based on many examples of your type car reporting higher twenties on the highway instead of 25 mpg. I am still a little concerned where your true timing is now. At this point I do not know what it was when these pumps were new but that is where it should be unless something exceptional is observed and other changes are made.

I await Cervans theory on what has transpired with him. It flies in the face of long standing observations from many previous posters. Yet if the relief valve is wide open and he has even more power I have absolutly no ideal at present myself of what is going on. At least he has a theory.

Update Edit..
Your spring should be removed again and length measured. New information posted by a fellow member indicates it should be no longer than 27mm. If by any chance it is still shorter stretch it to 26mm.

My 300D has a pretty rough idle...and it will nail for a second or two if I start from a stop too fast...once underway, however, it is very smooth, and has plenty of power...

I'm going to change the filters, and if that doesn't help, well I've got my eye on this thread.

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

Well as it turns out i actually lost power but the engine seemed to idle abit smoother. I thought that the engine had gained some power but i had not actually taken it for a full test drive, i had to leave for church. My theory was that the return pressure was pressurizing the intake pressure but that was not possible on further inspection but the good news is that the car is still driveable even without the spring. Now for the bad news.

My return lines are leaking (the home depot ones) that i bought and installed three days prior, the heat from the engine eventually cracked them. Right now i have new ones on there but they still arent holding the diesel from coming out so im going to be buying viton lines i guess there is no way around it. Does anybody know what the correct size fuel line is for the nipples?

__________________
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.

It is still early but to suspect this your fuel economy should also be sub standard as well. This whole area could evolve quite easily though as changes seem already to be present. It is not even known yet the exact pressure the injection pump maker designed into his relief valves. I am already very confused by the latest posting by Cervan on his thread for example. So watch and see how it all plays out first.

Added on since Cervan reposted.

Since you have good power and if the fuel milage is high average or close your problems in my opinion are not There . Any stretching of the spring that results in overpressure will result in two undesirable effects in your case.

In your case if you go there and stretch the spring you will elevate power but the long term effect may be destruction from running too advanced on timing and there is no way other than the milli volt method and considerable thought to verify this is happening. Yet I suspect it would be so. Also you would lose the ability to drip time the injection pump and retain the running refference timing. Give all this a little time to clarify.

From the limited knowlege gained at this point by a very small sampling and applied logic. If the fuel milage is substandard it is not unreasonable to check that the relief valve opening presure point has not deteriorated with time. This is done with a gauge. You correct things only if the pressure is wrong. At this point the actual proper pressure is an unknown.

Thank goodness I think your result is as it should be pretty well. That is if some of the hypothisis are reasonable . Your timing is retarded enough it is covering up the poor element feeding pattern present. You are retarded additionally by the setback caused by underpressure fuel in the pump plus the amount you dialed in to reduce the knocking somewhat. Power should be down below what you had before you stretched the spring. I was thinking that I would have to disgard all previous thought for awhile. Or the new effect was well beyond my limited ability to comprehend.

The possible saving grace for me at least until you posted again on your thread was it flew in the face of all those posts I remembered concerning problems in this area. At those long ago times I tried analysing what was happening to cause effects that were being reported. Like the widespread milage discrepancies on the 240d. Ultimatly I fixated on that particular item as I fully realised it could and would be found. The design is so simple that it could not be production tollerance variations. Five to ten percent was possible by them but not the reality of 15 to as high as 30 percent difference in milage under reasonable simular conditions.

Got absolutly nowhere until your experiment emerged and I realised the fuel supply to the pump was just not exactly only the fuel supply. It possibly had other functions. Or if it was not right a better expression is things would be different.. This is after my agony of examining so many reasons that could be the causitive factor of the milage discrepancies on 240ds and some other suttle effects. I never could find a glimmer of hope but knew something had to exist. Most important it had to be a common single item or denominator as no other combination of events could so consistantly appear without red flagging themselves in some fashion. Lets hope this is a breakthrough.

To be fair it is too early to be sure. Yet there is no other area on this type engine I have not seriously considered. Even this present area was slightly considered but discounted at the time. I felt if the elements were surrounded by fuel they were totally self loading. I should have recognised the clue when people claimed new fuel filters upped their fuel milage. Luckily I did not discount their posts yet failed to analyse the effect. It initially defied logic with my limited knowledge and ability. It now has turned around to bite me.

Cervan, without the spring if you think power is even less than with the spring before you stretched it. Mention it. So to speak it is the proof of the pudding. By the same token if the power is the same as when the spring was normal mention that. I hope it is not too close to call. If it is also mention that. Think it over. Your answer could verify the hypthesis almost totally. Or make it questionable by me at least.

If positive then the details would just have to be worked out. Absolute proof almost could be present one way or another by your answer. Indications are positive as well. I can almost forcast effects from tampering.

Nothing scientific has been done yet. Even though you may have made history in a way. Well it's been a long hopefully productive evening. I better get to bed.

I also have to and want to thank you for not throwing me off your thread. This combined effort might turn out to be the most forward move of any thread ever on this site if all goes well. Or it will fall flat on it's face. There is very little or no middle ground here I believe. Thanks again for stretching your spring and eventually loosing it. Or look at it another way. It's a better deal than driving into a tree. That must have been hard and it takes quite a guy to share it.

oops... No seat of the pants conclusion possible yet as you rolled back the timing manually when the spring was stretched I just remembered. Still any observation would be interesting to hear.

I'm going to install a fuel pressure gauge and see exactly how much change this makes.

What Mercedes has to say about this.

Note 26-27mm spring length and 11psi minimum and 19psi maximum settings.

Attached Thumbnails

     

Forced induction. I am a little suprised about the allowable range as timing seems to be impacted. Perhaps the posters stretching of the spring has resulted in a really large relief pressure change past the 19 lbs. This of course has to be also limited by the lift pumps ability to build higher pressures. It appears it can do pretty well. The lift pump may be more competent than I imagine. I wonder how much pressure that lift pump is capable of?

One thing for certain. If your measurement is below or even close to 11 psi then running timing will be retarded somewhat in my opinion. That is compared to the drip testing when the engine is running. Also suspect the elements are not loading equally as well at those lower pressures. Each element takes in a different quantity of fuel so the engine firing is a little imbalanced compared to what it could be. This easily impacts milage further. Especially on the fewer firing strokes of a 240d. That in my opinion would answer this more pronounced milage descrepancy on the 240ds with basically the same pump. It all fits together so well at last.

There may be an advantage to running in the mid range setting of their range of values at 14-15 psi or perhaps favoring the high side slightly.

A really good pump guy might be questioned in this area about his knowledge as there is no doubt something is going on. I still have to wonder if the pump manufacturer graphed this area well enough.

If the car you measure now gets good fuel milage for type we would know a little more. I wonder if it is on the higher side or in the 14-15 lb range that was suspected if so. The other effect may apply if the pressure if favoring the low end of the range. Only a mile or two less milage yet today that is signifigant for such little effort. Below 11 psi all bets are off. Between the poor element feeding profile and the then serious retarded timing milage and performance are going to be down. Already this is pretty certain to me.

It was also good that they post the length of an existing spring. So if fatigue is not too much an issue you can restore it to proper length and measure pressure. Thats if pressure is low of couse. It should never be found high with an old original spring. Thats unless the return line is blocked or seriously resticted somewhere.

Fortunatly when experimenting with the milli volt method I over advanced some examples of volkswagons on purpose so I am well awre of the syptoms the two gentleman have presented. An over advanced diesel can run pretty hard. It's just destructive in the long or short run depending on condition and strength of the engine. The additional degrees of advance as well I suppose.

I ultimatly blamed spinning the balancer on a volkswagon on my experiments. Plus for their pump the milli volt method was far more complicated in my opinion to get the right reading. The pump adjusted extremely easy compared to the 617 but what to set it to was complicated . That was in comparison to the 617 injection pump . It seemed to be the other way around a bear to manipulate but the proper mili volt peak reading was easier to identify. At least the right peak was compared and found to the drip method on one of the member participants cars. If their was any discrepancy it was only 1/2 of a degree. Probably just general wear it the system reflected that in the drip method. I think the milli volt measurement was the accurate one myself. Yellit duplicated the experiment several times and it always corresponded to the drip position I believe.
At that point I did not see the total picture or signifigance but do now.

The mercedes information may have been written at a time these effects were not totally recognized either. Or fuel was so cheap what was a few miles per gallon if that spread occured within the allowable range. Eleven psi or more availability would insure the elements recieved equal loading. Anything higher than 19 degrees would advance the timing past design tollerance compared to the drip test.

All the time and effort people have spent timing these engines not knowing the timing relationship between the static drip test and running timing of the pump might be heavily impacted just by the residual pressure in the pump while operating.. It turns out it was never a fixed relationship. We timed our pumps thinking everything was good by doing so. This may be why people working on these cars years ago on a regular basis might have much preffered setting the final timing by ear.

If you would fill in the details of where you take your pressure reading iand what it is/was it may help even more. I have no doubt after all this you are going to do it. Please post the details.

Thank you for finding the mercedes information on the relief valve as well. I will pm yellit and Sam so they can add their viewpoints. They both have good minds for this type of thing I believe. At least I am pretty well finished with this from my perspective unless I see someone doing something questionable.

The mili volt thing was endless and in the end because of design of hard lines etc not usable for timing 616/617 engines. Yet it still has enabled us to verify certain other things as we examine these engines. In fact it is the only way I could ever see of accomplishing them.

I also would like to see something like the filed mercedes pattents on the pre chambers examined in depth by a someone
that has access to them. I have a feeling they may have evolved near the end of production of the indirect diesel yet were never introduced into production.

My watching for a way to truly increase power or/and milage on these old indirect diesel engines has led me to this area as about the only possibility that makes sense. It seems to me to be the limiting factor. It is probably impossible to increase things otherwise. Maybe something on a members post will stimulate me. Othewise I again am out of ideals. Lets see what Yellit and Sam think. Two pretty good guys.

I seriously doubt that timing is significantly affected by the lift pump pressure (within reason). Obviously, if the lift pump were not producing any pressure that would probably reduce injected fuel quantities. The best way to find out for sure is to get someone with a piezo timing light and have them measure the timing with different pressures. But, since diesel is incompressible, pressure won't make any difference, unless its a question of filling time. In other words, if the passages to fill the pump barrel are restrictive, then higher pressures would certainly fill the barrel faster. This would be more noticeable at high rpm, max rack position.

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

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel

Where exactly is this valve located? On top of the primary fuel filter I assume? Amazing, the Bosch manual actually talks about "lengthening" the spring, and they give a length measurement...I'm assuming they are talking about stretching it?

Also, what is the different between nailing and knocking? Is there a difference?

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

This is from a 75 300D but its in the same location for all OM616/617 engines.

The relief valve is on the injection pump. If you follow the fuel return line back to the pump it goes to this valve I believe. For those willing to do it that do have milage problems. I see no harm in removing the spring and measuring it. Study the valves construction on the posted information. If the spring does not fall in the mid range of the length requirements specified by mercedes. Stretching it to the mid point of their suggested length should be a good thing. Do not stretch it further at present with the yet limited knowledge. Remember if the spring is overstretched you cannot remove the overstretch well iif at all in my my opinion. a caution is in order here. If you overstretch the spring you may need a new one. I do not know if you can buy a new spring without buying the complete relief valve assembley so be careful.

As for the timing not being swung around much I feel otherwise from both posters results. I feel before they adjusted their springs adaquate conditions existed to properly supply the elements with the designed fuel quantity especially on Cervans 240d. Maybe not on the 300sd. Upping the intended quantity of loading of the elements would advance the injection pressure release point from where it was. Hopefully restoring the relationship to the drip timing position of the pump. Quantity of fuel released would stay about the same I think. Yet more balanced loading of the elements. So otherrwise where is the new power coming from?

. I have no relationship indicated about the actual amount of the advance in degrees in relationship to the residual pump pressure yet and this may not be important. The important thing is to make sure you are in the proper range and a little more time may indicate where is the best point. Remember the original thrust for me was to try to find my way through the maze of apparent missing milage on many examples of 123s. The 240s especially. I never want to see someone do harm to their cars.

Lets collectively hope a lot of those springs have shortened over time with their constant 20-30 year load. Loaded springs can and do age and compress.
Without giving it a lot of thought even the piezo electric timing aid may not be sufficient to track changes other than to check the match between static drip timing and dynamic actual running timeing of the injection pump before the centrifical advance mechanisim activates. Again this may not be a requirement as the designed relationship should be present at 14-15 pounds residual presure. The restretch to mercedes recommended length almost automatically will put you there.Or really close. The only reason to read the pressure at this point is perhaps if you wanted to know you werer substandard.

This is answered very easy as well with no gauge. If the spring you remove is shorter with age than mercedes specs say it should be you are under the design pressure in the pump. Period. This does not have to be rocket science and everyone that is interested can think it through and act if they wish.

I personally want to know if the milage was improved or any other improvements noticed for those that the spring length required corrective action. Post that information so this will become a standard service proccedure as soon as possible. We may also get a feel if the problem is minimal or almost epidemic.

No reason I can think of at all to lengthen out the implementation time frame here. As for going toward the higher side of residual pressure within mercedes guidelines we can as a group examine that senario and it's implications later. It might aid cars operating at higher altitudes for example. Nothing in this area is known by me at present .

I just went back and reviewed the spring length post. I do not like the indicated tollerance spread at 26-27 mm spring length. We may have to gauge afterall to get into the mid range of indicated pressure or may not. Time will tell. 11-19 pounds resulting at that length seems an excessive spread for the same length springs unless part of the low side it is being caused by things like restrictive fuel filters. Or weak lift pumps.