Alastair,
'Dampens the inherent pulsations in the fuel return system.

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'84 300SD sold
124.128

This is one place where mercedes information might be limited in my opinion. The cigar hose also reflects the modulated resultant pressure right back into the injection pump through the relief valve when it is open. It modulates this by expansion and contraction under the impact of the increasing and decreasing pressure wave presented by the lift pump. There may be other effects as well I have not totally considered yet.

This is the principal function of the cigar hose in my mind. I can be wrong though but it should not really be considered too separatly from the pump itself. It is an integral part of the supply pressure function. It will take some time to find out if the cigar hoses age unless someone already has this knowledge..Even a rubber hose can cycle fatigue I imagine or change its stretch charactaristics with time.

Any difference fron the example employed to calibrate the injection pump will change the equal capacity of the elements to load. The injection pump elements are set up to operate over a portion of the constantly changing pressure spike from the lift pump after it is modualted. Remember the remaining modulated spike repeats consistantly with the elements in an identical fashion. Cycle after cycle.week after wek, year after year, it never changes. Thats another reason the lift pump has to be driven by the injection pump cam.

I just want it to be very clear that yes as the last post mentioned it does modulate the return pressure. Far more important though it modulates the total operating pressure in the injection pump itself.

Well, Thats VERY interesting....

Every M.B. W123, 240D/300D I have Ever seen here in the UK has a semi-rigid Nylon tube connecting both the Inlet and the press. reg outlet back to the fuel-filter....

NO rubber pipe like that illustrated above, at all....

Only rubber is used between the chassis steel pipe and the pre-filter and the return line from filter to the steel chassis pipe....

These pipes are quite obviously the original M.B. parts as there is a 'shape' to them and they are fitted perfectly,--and on all the three running M.B. 300D engines I own, And the one I'm currently re-building. All the same, Nylon pipe.....

Must be a specific mod for the USA/Canada.....Last night, I was thinking of a device that would smooth out the pressure-pulses, A type of 'pressure-accumulator', like a 'bell-jar' containing half air as a cushion, summit like a Citroen/SLS sphere, but without a diaphragm--Knowing my luck though, it would just chuck air into the pump and I would be kangarooing up the road!.....

A Flexible 'balloon' pipe, to smooth out those pulses --Now, There's an idea!

With regards to the bearing issue found very occasionally on these 61x engines.....

I personally always thought it was because the nos 1 main and 1 big-end are the last in the supply-line from the oil-filter, and also near their tapping, is the supply to the top-end, cam etc....

Also, nos 2 main gets its supply of oil from nos 1 main, via the Crank, and Not a drilling in the block!--(At least it does on the engine I have in bits anyway!--VERY surprised to see That when I dismantled it)

Maybe this occasional bearing-issue IS to do with the fuel delivery disparity between cylinders--A fuel issue like that would definitely Load the cylinders/bearings differently/unequally......Somewhere here, there was a thread about uneven engine-running causing rod-bending on the 350, but I just didn't buy that explanation--Who knows....?--Maybe low fuel-pressure caused it

I can check when the lift-pump is delivering the 'fuel-pulse', as I have a couple of pumps around in the W/S. I'll be doing some work on my 'Wagon' this weekend, and can pop the bottom off a pump and check when the lift-pump is delivering in relation to what cylinder is 'filling/injecting' etc....

This is turning into quite an interesting thread!--Where will it end!??

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http://i190.photobucket.com/albums/z...0TDnoplate.jpg

Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

Alastair, that cigar hose is on the fuel return side and connects the filter housing to the steel return line. If your don't have one it may have been swapped out at some point with a piece of regular rubber fuel hose.

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'83 300D 198,000mi Howard
'03 Saturn Vue CVT 75,000mi(wifeys)

A forum friend very early in this did mention a constant pressure fuel supply. At the time it did catch my attention. Perhaps useful at some point if the pressure could be remotley varied or controlled. These were my thoughts only a week or so ago.

Interesting that you should see no cigar hoses on your cars. If the same lift pump basically is used on our respective pumps. I wonder what or how your pumps are dealing with this pulse? Unmodulated the pulse must be at least from 0 to 30 psi or more every cycle. Perhaps the lower pressure number is higher because of the actual operating conditions. . Unfortunatly the constant pressure supply in the light of the little learned so far is not practical for our pumps over here unless they were re calibrated for it in my opinion.
Why you do not have a cigar hose could be benificial to know. And what they are actually doing instead. If the difference was properly considered it might give clues to further possible enhancements. On both sides of the pond.

Their still exists a possible silver lining a little later. I feel that once a good operating pressure has been obtained by many some elevation of it may be benificial again within reason. The timing issue will raise its head on diesel fuel I am pretty sure otherwise. Think 20-22 pounds under load operating fuel pressure for now. This is basically the upper end recommended limit it seems. Mercedes probably did not set that high a pressure during production. Now age and use may have further taken it's toll as well.

The proper timing correction at certain pressures can be done with the pizzo electric timing gear. Once we obtain the figures anyone can copy them if we get into this area.

I do not really trust timing these engines only by ear. The absolute last thing I want to see is someone damaging their engine.

Strange how things are slowly shifting to not examining the running loaded fuel pressure may damage your engine.

Right now I am just posting a lot to try making people think and contribute. I am a bit of a slow learner sometimes and can miss things. Tenacity is perhaps one of my stronger traits though. Dog with a bone may have nothing on me.

All I set out to do really a year or so ago was find the missing milage component so obviously missing especially on many 240ds. For the common good. In a way that task has been pretty well acomplished in my mind at least. . . All my observations till this came along did not really fit.

What was pretty iritating is it was only an engine and a pretty simple design at that. Yet in a way the thing was defeating me yet at the same time there existed quite a few solid clues.

Now where does this go from here in my opinion? For me much of the preliminary things have been considered and absorbed. My imagination or whatever will watch what others post. Something will come up or provide something to consider. It is almost inevatable as this is still almost a brand new area for consideration. It may not be over by a long shot. In fact this may just be the basic beginning.

I still think if the milli volt method had proved tractable and I had the faith to believe the numbers it was producing. . This problem would have become history much earlier. I still would like to see a dynmaic spread of the timing on the 616 and 617 engines. There may be room there to further improve efficiency.

As I also stated I believe but might be wrong of course. The number one rod problem would have been solved if a lubrication issue in my opinion a long, long time ago. There by now would have been at a minumin a modification for rebuilders to preform during their rework of the engines. These engines produce a superb high volume of oil pressure remember.

The ideal of the higher failure rate on the four cylinder versus the five cylinder engines way back when I questioned this caught my attention. I basically considered them the same engine. So why was the 616 failing at a higher percentage? Sure it was pulling the same load with less that may have increased bearing loading. Enough difference to destroy that rugged bearing I thought not. This basic simular engine pulls trucks.

I now believe it is because of the unbalanced lower quantity power strokes per revolution compared to the 617. It will never be proven but I will not run the risk.

Yellit ( Kevin) out pounding the road with little fuel pressure had to be stressing the number one bearing compared to the others from what I can grasp so far. It could be no other way if the number one injection pump element is the high pressure loader in the cycle.


As stated many times before I can and will be wrong from time to time. That is the price of trying to understand and change things. I am totally receptive to ideals. Lets get some more fuel pressure gauges installed out there to help this along. There is no doubt about it's worth in at least my mind. Milage will vary.

Sorry for being a latecomer to the thread.

I've a basic question about the lift pump - I've never had one apart on these engines, what's inside them, and how do they work?

Specifically, are they like the mechanical fuel pumps fitted to petrol engines with carbs, where the pressure is actually provided by a spring in the pump rather than by direct, solid mechanical action.

FWIW, pre-stretch mpg's, 26.5. Post stretch mpg's 28.6. Keep in mind this is only one tank since stretch. Will keep track and post the results.

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1983 300D 280,000
1983 300TD 125,000 Killed by oak tree.
1983 240D Sold
1986 Ford F250 Diesel 6.9l 169,000

Well that makes at least two of us that have never had one apart. I suspect it is a pretty conventional pump. Where the cam drives a rod that presses the diaphram. It is a constant supply type of pump as it produces constant overflow I believe.

There really nice thing is it is rebuildable at home with a kit at very little cost. Kit over here seems to average 6-10 dollars. No I am not absolutly sure of the mechanisim set up. I suspect the more direct diaphram drive because the operating pressure is well beyond petrol or gas engines fuel pumps with carborators.

Good news as it seems it is at least indicating miles per gallon are going the right way. I only wish you had a gauge installed so pressure at loaded speed could be known. Also at pre spring stretch setting. At present we are somewhat handicapped until Yellis (kevin) reports the results of his efforts as he has a gauge installed. Or indeed any other posters with a gauge as well.

If you get a chance. Can you talk to the gentleman you stretched his spring for and his shakey idle was history? With that much improvement there might be a milage or power boost he is noticing. Maybe both. Actually it is a forgone conclusion they both will be better even at this early stage. You probably have made him quite happy. We really do need all the information we can get at this stage. Nice to see some people really starting to get into this. Pretty soon it will self sustain I hope.

I am still waiting for the first 240d to increase milage from about 25 to 30-32 miles per American gallon. Hopefully the individual will install a pressure gauge before he starts and seek 20-22 pounds fuel pressure under load if his is curently less. Almost bound to be less in my opinion. There will be a power increase as well not that it is needed.

I feel if there is resistance to joining the something for nothing club it will stop at some point. Hopefully people will approach this area with a gauge. Only restoring function to high normal as well when burning diesel fuel. Until more is learned about further elevated pressures than are recommended at this point. It may turn out they are quite safe. Or require other minor changes to be safe. I for one do not know that information at present.

As an additional incentive I hope he thinks positive and wants to protect his number one rod bearing on his 616 as well if that pans out.

One gentleman is going to examine his spare injection pump this weekend if he gets time. He hopes to determine if indeed the number one injector sees the highest portion of the constant pulse when running.

That information would really be appreciated by a lot of 616 owners like myself. Strange but I suspect he will find the number one pump element is at the high end of the pulse. Could be wrong though.

The entertainment value of this thread as a possible item itself might be working out. We seem to be attracting more than a few observers. . We need gauge readers now to move ahead. Why not just check your operating fuel pressure under load?

>>Well that makes at least two of us that have never had one apart.

Thanks Barry!

Looking at the lift pump on my OM606, the outlet of the lift pump is the port closest to the body of the injector pump - to me, perhaps suggests the fuel is pumped on the return stroke.

If the pump is actually spring driven, then, I think the pressure fluctuations might not be so abrupt - a poorly damped gauge can easily make a small pressure change look much more dramatic than it really is.

If, however, the pump is a fixed displacement pump, then the pressure spikes will be higher.

I'm going to try to stretch mine this weekend.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Forced Induction used a normal undampened gauge and it was almost destroying itself quite a few posts back with engine at idle. A fluid filled gauge is a requirement.

Fortunatly the orientals have a cheapie liquid dampened gauge with a 2 1/2 inch face. This gauge is well distributed in north america as well. Yellit (kevin ) has two installed of the three or four he owns. He swapped gauges and the calibration seems good gauge to gauge.

Rebuilt my spare lift pump today....Inside is a steel piston about the dia. of a nickle about 3/4" long driven by approx 1" long,7mm dia. or so steel rod that is driven by the little steel roller slider that rides on the IP cam....
This piston lives under the big hex cap with a hefty spring that keeps the whole thing riding the IP cam lobe....
Input and output check valves are plastic and look like small flat top golf tees with delicate springs to return them to the polished chrome seats...about 1/2" dia and 3/4" long plastic valves....

The piston has no rings and just sucks and pushes the fuel from the input valve to the output valve...thats all that is in it......solid little thing.....the plastic disappointed me for a piece of quality German machinery but must work ok since they last so long.....

Also there is a small O-Ring that keeps IP oil from seeping past the piston push rod.....hard to see but I am lucky to have a Bosch IP shop owner as a friend that made sure I knew about the o-ring ...I would have missed it during the rebuild probably.....It did have a lot of slack around the rod....quick and easy to rebuild....

I rebuilt it because I have stretched my ball/spring to 31mm and still only get about 14 PSI out of the pump...will replace tomorrow with my rebuilt Lift pump and post back......

The 0-30 psi gauges I use only have about 1~2 psi oscillation above idle...made in Ohio ...NoShok brand 900 series glycerin filled...bout 25 bucks each.....they have a website...

__________________
1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

Nice to see you Yellit (kevin) post. You have done it again. I fear a lot of spring stretchers are in somewhat simular situations. May have had really substandard pressures. Stretched their springs and have gotten some gain that feels good and figure they are really up pressure wise.

This may not be exactly so. Your case may be more typical than not. Kevin went from about five pounds to 14 pounds load test by removing obstructions. He then tried to increase to about twenty pounds by stretching his spring. No more upward potential could be realised. So he has rebuilt his lift pump. By having a gauge he became aware of both his initial difficulty and his secondary current one.

Happy to hear the lift pump is a quality design. Your description of the intenals was excellent. No worry about abusing a diaphram now. I was a little concerned right along if there was a diaphram. Would it like the increased load? The metal piston does not care at our pressures.

Now on to the gauge. I will describe my cheapie. If stood vertically there is a top gap of about 5/16 inch with no liquid. There also is a rubber bung to contain the fluid at the very top of the gauge. The red printed bar portion of the scale stops at 2 bar. The black psi scale is a little longer ending a little past the red bar by about 3/16 inch at 30 psi.

There is no indication on the packaging or gauge that it is of Chinese manufacture. But the source of purchase is princess auto and that pretty well is interchangeable with chinese. Same as your harbour freight.

On the back of a cardboard included in the package is a description on a bar code sticker. Gauge 2.5" 30 psi gly. Also of note on the front of the cardboard this pressure gauge is safe for use with oils and gasoline.Not oxygen or acetylene. Valley instruments is the brand label on the packaging but no brand on the gauge or country of manufacture. This all lead me to believe this item is well distributed by many methods in north america. Obviously a repackaged of a sourced item by the company.

I wonder if this is simular to Kevins? There has been a problem in the states with selling chinese goods by many firms pretending one way or another they produce them.

I have watched the fines being handed out for this activity but they are minumal and infrequent. Just a cost of doing business and worthwhile if you pretend it is american made. I hope I am wrong with your gauges. Probably am. One more identification item. On the back there is a recess of about 1/2 wide by three quarters tall by eye. Anyways as always well done Kevin.

Lets see now a running load pressure of 20-22 pounds from 14 pounds will do quite a lot I hope and expect. No need to rush out and aquire a five point seat harness yet though in my opinion.

It aleady may be possible people using fuel mixes like yourself may still have quite a bit of headroom beyond 22 pounds. We will not know for positive until we get a lot of gauge readings and results posted.

There is absolutly no reason not to suspect that low fuel pressure impacts cold start ability in a negative fashion either. Probably not detectable above forty five degees. On this point I may be very wrong. It might impact at all temperatures. Below about forty degrees just may even be more of a signifigant problem.

Too big of a spread out there of cold start difficulties always blamed on compression usually. Maybe we can get into this after awhile as well.

Someone expressed the well expressed thought today basically of. Where is this going? Or whats next. We have to get those gauge sales up first.

Final item tonite as I have to get to bed. The poor deprived wife demands it.

It never seems it's ever going to end in this area. If that small o ring on the lift pump rod disinegates could the lift pump intake and feed some base oil as well? Or does it feed fuel oil into the base oil supply when defective? It will be one or the other or both even if the quantity is low. Another source of smoking? We will find it someday Jimmy. Lets see 1500 small exchange injections at about 55 mph per minute. About three hundred at idle.

Looks like the site maintenance lost our last several posts about stretching the wrong spring......

The lift pump spring is what determines the pump output pressure.....

Number cruncher figured this out.....the pump dicharges on the return stroke.....(spring pressure only)....the IP cam just pushes the piston back for the intake stroke.....
To increase pump output pressure...the big spring under the large hex cap could possibly be stretched or shimmed.....
Going to try that on mine today...since my pump can only put out about 12~13 psi max......will post back results....

__________________
1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)