I know the IP from my 83 240D parts car has a pressure relief valve. I sold that IP and part of the deal was to throw in an adjustable pressure relief valve and I remember pulling the old one which had a ball and spring in it.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Who ever said "its easy too read the numbers off an IP thats installed on the car" . Takes your best pair of glasses, a couple mirrors and good light.

The IP in question (1980 616, US) RW 375/2200MW 27

The three "parts car" IPs all had relief valves. I don't have the exact years but they are all from US spic W123, 240Ds. These IP were not on the car

IP#1) RW375/2200MW 28-1

IP#2) RW350/2200MW 21 I had this one marked 1978

IP#3) RW375/2200MW 27-1

Note The IP in Question has the same numbers as parts IP #3 except for the -1 at the end, which, I think, indicates #3 has an auto trans (which it did)

Like I said, the numbers on the IP in question being still installed on the car, were very hard to read but I'm pretty sure they are correct.

this doesn't tell me anything except I screwed up and didn't install the pressure relief valve on my 80 240D when I rebuilt the engine years ago, but thats imposable because the car runs like a scalded cat.

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Long shot but the return line might be obstructed. I have been thinking you might actually already be overpressure. They wil be quite a bit quicker then.

Are you seeing a good return flow? By the way I have never felt overpressure within reason hurts much of anything.Other than throwing the calibration of the injection pump out a small amount. Nineteen pounds is basically completely safe and just might shift the calibration just enough to make the load a very small amount heavier on the rear of the engine.

I am pretty certain that at very low fuel pressures the number one cyinder is taking too much of the loading powerwise compared to the other cylinders.

Am I certain no. Yet everything I come across seems to further reinforce the ideal. Originally it was just a suspicion. Now it would take a lot to undo the ideal. There is just too much circumstancial evidence now to ignore. The evidence even keeps increasing with time.

. On neglected cars or cars that almost never had their fuel filters changed unless the car basically stopped. Or for other reasons always had chronically low fuel pressure in the base of the injection pump. On these cars there may have been abuse of the number one rod bearing. Correcting the fuel pressure may help even up the actual wear somewhat. It takes a lot of miles till this effect is a real problem. For the size of the engine the torque and horsepower output are not that high. So the number one cylinder being overworked in relationship to the others takes time and many miles to show the damage..

The numbers you quote here are the governor serial numbers not the pump. It doesn’t matter anyway because all the M and MW pumps must have the by-pass valves. Apart from keeping the L/P chamber pressurized between 12 & 20psi they provide an important function in keeping air from the return line getting back into the pump L/P chamber and causing difficult starting.

The L/P chamber pressure is not critical by any means and it is not surprising that your car runs well without it even at the top end. At max. RPM and full throttle suction alone from the metering element chamber, through the supply port, may not be enough to prevent some cavitation resulting in a loss of power at the top end. Therefore that extra “push” through the supply port from pressure in the L/P chamber eliminates any chance of cavitation.

Apart from the consideration above fuel supply pressure has no effect whatsoever on the H/P fuel circuit delivery, engine performance, power, economy etc. – not one iota!

BTW – The “banana” hose was a fix to prevent the rubber “leak off” pipes from blowing off the injectors when they changed from the steel lines. The air in it provides a cushion and solved the problem.

I would be fascinated to hear your theory behind these assumptions.

__________________
Beagle

I got the gauge this morning. The 240D in question shows 2.5 lbs at fast idle. . This is odd. I'm tempted to install a relief valve from one of my parts IPs, but common wisdom & laziness tells me to leave it alone, its a very quick 240 and I hate to mess with a good runner.

The Euro 300TD at fast idle shows 11 lbs.

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

I think if I don't put in the relief valve I will always wonder. Unless theres another reason not to, besides the above mentioned, "sleeping dogs"..I should.
If my IP explodes because it was only designed for 2.5 lbs, perhaps an experimental model, what the heck I ran the test for at least 5 minutes and it slowly got up to 2.5lbs max. I did the 300TD, 11lbs, which indicated the gauge was working. Any reasons besides the dog thing to NOT put one in?

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

What's odd? That you're getting 2.5 psi instead of zero? The lift pump pushes a lot of fuel, even without a check valve, there is restrictions in the lines and 2.5 psi sounds about right. I'd recommend putting in the check valve, it should make your car run even better.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Well for starters the lift pump recycles once every injection pump rotation. If no to little system resistance is found past the secondary filter the rise and decline in fuel pressure present in the base of the injection pump might track the pulse of the lift pump every input cycle. The lift pump is designed to hold pressure against a resistance load to preform it's intended pressure averaging design paremeter. It cannot do this properly against basically no presure restriction load.

If this were so some elements will be relatively starved compared to a constant feed pressure through the total lift pump cycle.

As for low pressure having no observable defect in comparison to decent pressure is wrong.Many have already found out on our site that pressure elevation to decent numbers does many things if theirs was substandard initially.

The difference is quite noticeable. The injection pump when being calibrated must have the lift pump delivering at a certain pressure. This indicates that perhaps calibration with lower pressure will be different. Even mercededs technical literature wants about fourteen pounds pressure present and many injection pump shops enable the calibration at 19 pounds pressure as it is benificial over the recommended fourteen pounds.

It took me a lot of thought and time to originally get by all the proposed reasons that the number one cylinder of the 616 eats bearings. That is at a greater rate of incidence than any other cylinder.

I worked on this problem because a member asked me why was it always the first cylinder problem on the 616 engine. If it was what was projected mercedes would have done some form of running production change. This block was in production for a very long time remember. My bet always has been that the initial recharging of the lift pump occurs just before the number one element loads. . This increases it's timing somewhat as well in comparison to the remainder of the elements as the temporary spike in pressure with an open return has passed.

The nail in the coffin so to speak came when some europeans eventually mentioned the problem does not seem to exist in europe. The only difference between their 616 engines and ours is the injection pump and perhaps some small component function of their fuel supply circuit. The american model cars lift pumps put out less overall pressure than the 617 five cylinder cars as well remember.

So with filter obstruction etc it is not unusual for the injection pump to see less operational fuel pressure. Just not changing the fuel filters more often on a 616 than a 617 might produce a difference for example.

There is much more circumstantial evidence as well. This abnormal loading efect of the number one cylinder must be present for a long duration to do the damage that is reported.

Anyone that wants to speak to a injection pump rebuilder will find that they might hazzard a guess at what is going to happen operating an injection pump at basically no pressure after the pump was calibrated with 14-19 pounds pressure. A lot of shops calibrate at 19 pounds because the power output is better after the injection pump rebuild by the way.

This whole mess has brought me to the point of recommending several things. Check your pressure with a gauge. If low change the filters out. Clamp off the return line to see what pressure developes. It should be in the area of the manufacturers rating of the terminal lift pump output pressure.

If still low clean the tank screen and rebuild the lift pump.Or open the line from the fuel tank to see if decent flow is there before rebuilding the lift pump. Open the closed off return line to examine the pressure. You at this point have no abnormal restrictions in the system. So if the relief valve is calibrated properly the pressure will be where it should be. If low. Deal with the relief valve. If too high clean the return line. Usually the relief valve will not obstruct with residual garbage in the fuel. It may not close though in that situation.

Try not to question my thoughts at this point. At first I believe that a lot of members questioned my sanity when I arrived at this conclusion. If I had not ventured into this area a lot more 240ds would have finished their number rod bearings off by now.

If you do not install a fuel pressure gauge on your 616 fuel supply system at least change the fuel filters at the recommended time and milage interval. That block will run a long time with substandard fuel pressure in the base of the injection pump. It will not actually be running as well as it should either.

As for leaving a system at 2.5 pounds operational pressure that would be a serious error in my books. Why not just try a working relief valve on that system. Check the difference with your gauge pressurewise and mention the results of any performance change on this thread. You can always revert back to no relief valve if you wish.

If you buy a 616 with low operational fuel pressure and assume it may have been this way for a long time. You may want to plastigauge the number one rod bearing. Intervention at this point in time may save you greater difficulty down the road. no major wear found no current issue. This engine is so noisy you could miss the start of a light rod knock very easily.

As for the banana hose just being there to prevent the return lines being blown off the injectors. That is a new spin to me and could be true even. All I know is the cigar hose seems to have many more functions than currently thought. I have wondered for a long time why the cars with the european injection pump do not have one. There is some unknown difference to me in their operational set up. Maybe they all blow their return lines off?

To me a sensible cheap upgrade is to change the spring in the lift pump to the one found in the five cylinder 617 turbo lift pumps. Even a used one is fine. Then the lift pumps pressure output will be better able to deal with lesser amounts of fuel filter restriction without the injection pump seing low pressure earlier than with the original lift pump spring.

Now a challenge for the gentleman running 2.5 pounds pressure at present. Warm the engine up. Take a meter on the lowest voltage range. Hopefully 200 milli volts.

Read the voltage on each glowplug between the plug and the block. Record the numbers. Do the same identical test with the pressure increased to the normal range. You may be able to read the voltages from the glow plug harness connector. But the ground has to be the engine. Not the negative terminal of the battery. I do not know if the voltage change will be enough to show any form of incremental change.

It is a toss up in my mind but you would be the first person to exercise this option in my opinion. Any difference between the two sets of readings will have an explanation if there. My concern is it may not be enough of a change because the effects we talk about are small when it comes to temperature changes in each combustion chamber. At least give this some thought as it is so easy to do.

Well for starters the lift pump recycles once every injection pump rotation. If no to little system resistance is found past the secondary filter the rise and decline in fuel pressure present in the base of the injection pump might track the pulse of the lift pump every input cycle. The lift pump is designed to hold pressure against a resistance load to preform it's intended pressure averaging design paremeter. It cannot do this properly against basically no pressure restriction load.

If this were so some elements will be relatively starved compared to a constant feed pressure through the total lift pump cycle.

As for low pressure having no observable defect in comparison to decent pressure is wrong.Many have already found out on our site that pressure elevation to decent numbers does many things if theirs was substandard initially.

The difference is quite noticeable. The injection pump when being calibrated must have the lift pump delivering at a certain pressure. This indicates that perhaps calibration with lower pressure will be different. Even mercededs technical literature wants about fourteen pounds pressure present and many injection pump shops enable the calibration at 19 pounds pressure as it is benificial over the recommended fourteen pounds.

It took me a lot of thought and time to originally get by all the proposed reasons that the number one cylinder of the 616 eats bearings. That is at a much greater rate of incidence than any other cylinder.

I worked on this problem because a member asked me why was it always the first cylinder problem on the 616 engine. If it was what was projected mercedes would have done some form of running production change. This block was in production for a very long time remember.

My bet always has been that the initial recharging of the lift pump occurs just before the number one element loads. . This increases it's timing somewhat as well in comparison to the remainder of the elements as the temporary spike in pressure with an open return has passed. So the remaining elements are loaded at a lower pressure. There are indications that this is progressivly more so the later the element is in the chain before the next recharge cycle of the lift pump.

The nail in the coffin so to speak came when some europeans eventually mentioned the problem does not seem to exist in europe. The only difference between their 616 engines and ours is the injection pump and perhaps some small component function of their fuel supply circuit. The american model cars lift pumps put out less overall pressure than the 617 five cylinder cars as well remember. Even though the europeans fuel is also better I have had to eliminate it as much of a factor in itself. It should worsen the problem not lessen it if prevelant there in my opinion.

So with filter obstruction etc it is not unusual for the injection pump to see less operational fuel pressure. Just not changing the fuel filters more often on a 616 than a 617 might produce a difference for example.

There is much more circumstantial evidence as well. This abnormal loading efect of the number one cylinder must be present for a long duration to do the damage that is reported.

Anyone that wants to speak to a injection pump rebuilder will find that they might hazzard a guess at what is going to happen operating an injection pump at basically no pressure after the pump was calibrated with 14-19 pounds pressure. A lot of shops calibrate at 19 pounds because the power output is better after the injection pump rebuild by the way.

This whole mess has brought me to the point of recommending several things. Check your pressure with a gauge. If low change the filters out. Clamp off the return line to see what pressure develops. It should be in the area of the manufacturers rating of the terminal lift pump output pressure.

If still low clean the tank screen and rebuild the lift pump.Or open the line from the fuel tank to see if decent flow is there before rebuilding the lift pump. Open the closed off return line to examine the pressure.

You at this point have no abnormal restrictions in the system. So if the relief valve is calibrated properly the pressure will be where it should be. If low. Deal with the relief valve. If too high clean the return line. Usually the relief valve will not obstruct with residual garbage in the fuel. It may not close though in that situation. Consider making the presure gauge a permanent fixture in the car. At the very least it will tell you when a filter change is due. Or when you took on a load of really dirty fuel.

Try not to question my thoughts at this point. At first I believe that a lot of members questioned my sanity when I arrived at this conclusion. If I had not originally ventured into this area a lot more 240ds would have finished their number one rod bearings off by now. A lot more will eventually fail just because people will not think things through.

If you do not install a fuel pressure gauge on your 616 fuel supply system at least change the fuel filters at the recommended time and milage interval. That block will run a long time with substandard fuel pressure in the base of the injection pump. It will not actually be running as well as it should or could be though..

As for leaving a system at 2.5 pounds operational pressure that would be a serious error in my books. Why not just try a working relief valve on that system. Check the difference with your gauge pressurewise and mention the results of any performance change on this thread. You can always revert back to no relief valve if you wish. You are not disturbing a sleeping dog kind of thing as returning the system to 2.5 pounds is very easy if desired later.

If you buy a 616 with low operational fuel pressure and assume it may have been this way for a long time. You may want to plastigauge the number one rod bearing. Intervention at this point in time may save you greater difficulty down the road. No major wear found no current issue. This engine is so noisy you could miss the start of a light rod knock very easily.

As for the banana hose just being there to prevent the return lines being blown off the injectors. That is a new spin to me and could be true even. All I know is the cigar hose seems to have many more functions than currently thought. I have wondered for a long time why the cars with the european injection pump do not have one. There is some unknown difference to me in their operational set up. Maybe they all blow their return lines off? The residual pulses from the elements have to be averaged or moderated in some fashion. If your cigar hose is rock hard with age change it out. Replacing it with a piece of hard hose will cause running issues on some 617s is proven. There is even a small chance that a system not developing enough pressure to open the relief valve. The unmoderated pulses present in the injection pump from the elements may have some form of undesireable effect. The reason to have normal pressure as well from the lift pump is to enable the cooling of internal parts of the injection pump from the excess fuel transiting through the injection pump.

To me a sensible cheap upgrade is to change the spring in the lift pump to the one found in the five cylinder 617 turbo lift pumps. Even a used one is fine. Then the lift pumps pressure output will be better able to deal with lesser amounts of fuel filter restriction without the injection pump seing low pressure earlier than with the original lift pump spring.

Now a challenge for the gentleman running 2.5 pounds pressure at present. Warm the engine up. Take a meter on the lowest voltage range. Hopefully 200 milli volts.

Read the voltage on each glowplug between the plug and the block. Record the numbers. Do the same identical test with the pressure increased to the normal range. You may be able to read the voltages from the glow plug harness connector. But the ground has to be the engine. Not the negative terminal of the battery. I do not know if the voltage change will be enough to show any form of incremental change.

It is a toss up in my mind but you would be the first person to exercise this option in my opinion. Any difference between the two sets of readings will have an explanation if there. My concern is it may not be enough of a change because the effects we talk about are small when it comes to temperature changes in each combustion chamber. At least give this some thought as it is so easy to do. I can almost bet that your idle will be better, power greater or the feeling of it. Plus the engine will run in a better power balance situation. Some even quoted the engine sounded quieter or different on the highway after the pressure correction.

Certainly the running at 2.5 pounds may not cause you issues over your period of ownership. Eventually it probably will though. Running at nineteen pounds pressure will not for sure. I also preffer engines runing with their best power balance point possible..Last for now but not least. Some have reported that a filter change increased their average miles per gallon. Enough posters reported this to validate it. The only thing that obstructed filters do is lower the pressure in the base of the injection pump. If not so badly restricted that the engine quits. Superficially one might think that less fuel available the milage would be better. My contention again is the power balance is way off at lower pressures as well.

I had really thought we were past the validity of it is better to have the proper operational fuel pressure in the base of the injection pump than not to have it. It is a real cheap area to correct things in if required as well. To me it is just the requirement of a good tune up. Even the manufacturer of the fuel injection system wants decent presure. Or do we still have people that are smarter than them present? It is unfortunate that the effects of low pressure are not mentioned in their shop manuals. It might have saved thousands of 616 north american version engines by now. We were averaging almost one poster a week had lost their number one rod bearing for quite a period of time. That was just from members on our site. The loss of engines must have been much greater with all the 616 owners in north america at that time.

It seems odd that the car is running so well. I'll install the valve tomorrow. I checked the spring length on one of the parts IPs and it was something like 20mms. I seem to remember 27mm for the correct spring length?

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

BTW, my banana hose was removed long ago and never had the return lines pop off.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Well I guess you answered my question about why I should install the valve.
I will report back tomorrow. Thanks for the detailed run down, I will see if I can get the miliamp numbers before and after.

Both my Euros came to me with cigar hoses.

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Funola is correct Steve. The reality is that you are not getting zero pressure at any stage and pressure rises along with rate of flow very significantly due to friction and restriction in the long return pipe to the tank.

A very simple example is a 20M garden hose – check pressure at the tap and again a couple of feet from the end.

The bottom line is that you don’t have a problem. I would advise that you fit the valve anyway if for no other reasons than:

1) It prevents air leaking from the return line back into the chamber.
2) It prevents fuel draining from the L/P chamber through leaking lift pump valves back to the tank.

Very few people did but they had to fix the problem. I threw mine away years ago too and have never had a problem. MB sent out a TSB many years ago stating they should be changed F.O.C.

__________________
Beagle

Some euro version have them from the factory some not. I have often wondered why. All north american version injection pumps have them I believe.

Removing the cigar hoses makes a difference in some cars and in others not as much . Since the difference on many may be too suttle to notice my thought is to leave them in.

The difference is not always that suttle. Your liquid dampened gauge tends to average what the pressure present is. So does the cigar hose to a limited extent with the relief valve totally open. You may have stumbled on to something important if the performance is not enhanced overall with proper pressure.

In your description I would expect a high pressure point of perhaps five pounds or higher number dropping lower through the lift pump cycle at idle. To read this event correctly would require some money for equipment and effort. As it does not seem important yet it is not worth doing. I do agree with the the poster that at highway speeds your average base pressure might be higher in your particular situation if more flow or volume from the lift pump is occuring. The restriction of the return line remains pretty well a constant. Or actually increases when more flow is present by effect.

What I expect to see is your milli amps readings to be slightly higher at higher fuel suppy pressures. Or the mathamatical difference average of voltage spreads on the glow plugs to be less at greater base pressure.

Enough of a temperature change to detect with the limited equipment is one of the questions you might answer. The glow plugs being matched for this particular test is not a requirement.

If the idle sound changes there must have been changes in the combustion chambers. Any difference changes the temperatures. Or there might even be detectable readings that reflect changes with no noticeable difference.

The numbers you record should be retained as a baseline anyways. If problems ever develop with that engine they might help out in the future. Milli volt testing can be pretty sensitive. We just do not know how sensitive yet. Try to make sure the car is warmed up to operaional temperature for each milli volt test.

This may become one of those threads that become watched by many on site. You can never forcast where they may lead.

Just a few quick observations……

Are you sure about that?

It’s called “Placebo”

As Dickens Mr McCawber would say: ”I think you’d better think that out again!”

Oh Dear! I’m afraid you have still not figured out yet how the lift pump works!
MB sent out a TSB many years ago stating that early models without it should be fitted F.O.C. It will be filed away in my office somewhere but I have better things to do with my time than copy and post it here. All European models do or did have one fitted originally. Be careful not to let your imagination run away with you.

__________________
Beagle