240D is p/n FP/K22MW21

300DT is p/n FP/K22MW22

What's the difference?

__________________
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

1

__________________
'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

my bet is it flows about 30% more fuel... n/a vs turbo, and 4cyl vs. 5cyl...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

There just might be a different pressure determing spring in the unit. If in doubt and part numbers are different I would drop a 5 cylinder spring in. Even a used one should suffice. Somewhere or other I thought someone got a lower than normally expected pressure out of a rebuilt 240d lift pump. That could have been for other reasons though.

In general theory one lift pump should be the same as another on these engines. Yet as you mention they have different part numbers. Volume of fuel I cannot see as being a particular issue between a five and four cylinder engine. Output pressure may be slightly different though. If so it is beyond me why this would be so at this time.

Both the five cylinder and four cylinder seem to use approximatly the same amount of fuel in general. Quicker fuel availability might be of some benifit with a turbo engine. Or the ability to sustain volume evenly. This would be reflected by a larger bore in the lift pump I would suspect on five cylinder versions.

Bosh probably kept some information to themselves as propiatary from mercedes. We certainly have not learnt the ins and outs of the fuel supply system or the obscure from mercedes service information.By todays standards it is a pretty simple system yet still has some spins on it.

you seriously don't think an extra cylinder, and a turbo would need additional fuel capacity?

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Just checked my copy of the Mercedes tech spec 1981 page 166 which shows the different p/n's for the lift pump (Mercedes calls it the fuel pump) for the various diesel engines. The test specs for vacuum at lift pump inlet and pressure at lift pump outlet are all the same!

__________________
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

What I think is irrelivent. Bosh may have had some issue or thought they did. If so it is lost to history probably. The only increase in fuelling required I can think of is on hard acceleration with the turbo and the alda pouring more fuel in.

In an attempt to keep the output pressure profile of the lift pump as constant as practically possible. They might have changed the lift pump design a little.To properly service all loading considerations.

Or to be specific. They also did not want the relief valve to close at any time during the cycle as filter obstruction grows. The relationship between the cigar hose and pressure spikes are upset if this occurs. . The lift pump only charges once each complete injection pump rotation as you know..

As I stated already somewhere or other the available output pressure seemed lower or was reported as such on the 616 lift pump. Real or imagined but not absolutly established.

My guess is also the rod failures where randomly starting to surface by then so bosch changed the lift pump somewhat. Remember mercedes introduced this system from bosh initially in the 1930s. They had time to find the short comings of their system.

It is still my opinion bosh would not want to come clean for the number one rod failures either. Even though in most indications the fuel supply system is the culprit in my opinion . They are caused by inadaqate general maintenance of the fuel supply system.

Particularily the lack of fuel filter changes. On a car costing as much as these did at their time. A dash warning light indicating sub standard fuel pressure supply was present in the injection pump might have been incorporated. Even my cheapest diesels have had a water in the fuel warning light for example.

.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

There were three or so different springs that were used in 61X lift pumps depending on the application. The 616 typically had a weaker spring with a max of 15 PSI dead head pressure, (for reference, I have two of those), where as the 617a had a stronger spring with a max pressure of around 30 PSI when dead headed, (for reference, I have one of those).

If you search for the fuel pressure adjustment thread, I think it is called anyway, that Craven started, some where near the end, a member found several part numbers and specks for the various lift pump springs that were used.

There are some issues that present them selves as the strength of the lift pump spring is increased beyond that of the 616 spring. I am using a stronger spring in my 616 that can make over 50 PSI when dead headed, ( I am running 30-35 PSI), and I found that the fuel pressure would jump around quite a bit because the fuel could not react to the demand signal quick enough. I believe that Granimal, (sorry for butchering the name), had the same issue when he put a 617a pump on his 616 turbo. I found that by using a large primary filter and positioning it vertically, the air pocket would allow a quick pressure drop so the fuel could fill the lift pump, and then, at a smoother rate, refill the filter. The fuel does not want to move in pulses, too much mass.

Read the thread I mentioned, there is a lot of information there.

The relief valve should always flow to maintain an average supply pressure in the injection pump. If the volume it handles is increased beyond the capacity to easily flow through the relief valve orfice .The constant pressure element of the function in the injection pump may be somewhat more unstable..

Also if the lift pump is generating such low pressure. It is yet another coffin nail for the concept of the more frequent first cylinder rod bearing failures on the 616.

As any obstruction like a partially dirty fuel filter start to lower the fuel pressure in the injection pump.Or the lift pump is getting tired. The number One cylinder will in all likely hood be getting more fuel than the other injectors. Or the sequential timing of the pumps elements is compromised by inadaquate filling of the remaining elements in comparison. An unbalanced engine condition has been created. An increased proportion of the normal distributed loading has been displaced to the number one cylinder. So it wears much faster over time.

There is not a shred of proof that this is a false assumption so far. Not totally proven but still highly suspect.Everything keeps pointing there.

Whatever as the kids say. There is a serious penalty from letting a very low base injection fuel pressure continue over a long period. There is just no reserve pressure available like on the higher psi 617 lift pumps to overcome limited obstructing of filters.

That is why the failure rate of the 617 is less in numerical comparison. I thought this was a factor of more power strokes on the five cylinder. Of course that still helps a little. Now the principal culprit looks like a marginal fuel pressure design of the 616 lift pump unless you really stay on top of the system. There is a substantial reserve pressurewise on the 617s in comparison.

I know not enough people are changing out their fuel filters at reasonable periodic points. Without a gauge in the system this is the inverse of saving money in my opinion or really the wrong place to try it.

Hope your car is runing well and fairly fast. Have you gotten a seat of the pants feel about the fuel economy yet on VO reciently? I know your last post on the fuel economy struck me as excellent.

Another valid contribution you probably have uncovered because I almost totally forgot it. Is that the 616 developed so much lower lift pump pressure. It is starting to provide a pretty clear picture of the probable reason so many
240ds get mid twenty miles per gallon or less. Yet a lot are also broaching 30 mpg or close. I always watched that pronounced gap. Now most people should be able to get the thirty miles per gallon or close if they pay attention. Those at 25mpg or less highway may also be putting their engines at risk. Time will tell if we get this all right.

Anyways as I suspected you are not going back to low pressure normal operation. I really cannot blame you and see no particular downside in your situation. Your persistance and efforts have to make some believers out there.

Post your current fuel milage at some point to help motivate them if you have been tracking it still. Once there are enough believers out there this area should take on a life of it's own.

I have not wanted to appear as a dog with a bone any longer for quite awhile. It is just too important an area to let die..If I held any belief it does not really matter I would drop it like a hot potato. I also want to move on to other things. This broken record syndrome is punishing. Still every new person working in this area seems to make some kind of valid new contribution.

In what seems to me a Moment of Inattention the Lift Pump/Fuel Flow/Pressure
Relief Valve Collaborative Information Sharing took a Quantum Leap in Understanding.

If I unnerstan Barry correctly,Improper Fuel Flow CAN be a major cause of
#1 Rod Bearing Failures in the OM616s ? ("Overfueling" for lack of better term)

'Logic would dictate It also occur in the OM617s and the OM 60X series. ???

Mayhaps,After excoriating Stuttgart all these years about
(What I considered a "Fairy-Tale")
the theory of Crappy US Diesel causing the demise of the 350 "Rod Benders"...
I Was Wrong???

Fuel Quality and Flow are Much more of Importance than Previously Understood?

__________________
'84 300SD sold
124.128

I was actually going to have a serious look into the 3.5 rod benders at one time. I suspected it was a combination of design shortcomings. Some of them never discussed yet.

The first thing that needed some research was did most defects occur towards the front of the engine or where they random cylinders?

Because of the thin generally low stability of those 3.5 cylinder walls. Proper power balance must be maintained and checked on a yearly basis. The 616,617 and 3.0 603 plus the 2.5 602 seem to have an adaquate reserve of strength to tollerate the abuse for a long time. There is no tolerence or not enough strength in that 3.5 block to allow this condition.

Wisely for the state of my mind and seeing how difficult it was to get people even to check their fuel pressure at all. Even on the 616 and 617s to maintain their cars properly and maximise milage, idle,power, and longivity. (no more rod failures).Plus deciding I would not buy a 3.5 I backed away from further considerstion.

Someone with the interest or a 3.5 engine could pursue this further. You would want to use the milli volt method carefully and properly to make sure all cylinders are at the same burn temperature. A 3.5 needs more frequent fuel filter changes or a gauge installed. Otherwise running with a power imbalance is probably a relatively short terminal ideal for those engines. The 616 and 617s will of course tollerate it for a long time because of their more robust strength but eventually both can fail from it in my opinion.

I broke this post into two sections as you have two items at least mentioned. The fuel pressure in the base of the injection pump does determine many things. The problem is compounded in my opinion by these cars remaining fairily serviceable with substandard pressure.

The engine can eventually alert you the fuel supply system is defective in a serious fashion. It probably also is time to mention why I preffer to see the system at 19 pounds pressure rather than the 15 or so suggested by the manufacturer.

It just might slightly tilt the power balance in the engine just a small amount away from the two front cylinders. Remember the injection pump is calibrated at whatever the relief valve pop pressure is. Raising the relief pressure a little is going to shift the calibration of the pump. So cyinders number three to four or five or six depending on the engine you have take on slightly more of the load than a well balanced engine powerwise would have. Yet not enough to create damage or noticeable being only a very moderate shift if any.

There in my opinion is going to be more wear on the number one rod bearing existing. If the engine has been run with low pressure for a prolonged period of time. Hopefully this can compensate a very small amount for that issue.

Again the 616 is in serious danger as it now sounds like the 616 system by design has almost no reserve pressure at 15 pounds output from the lift pump. This compared to thirty pounds pressure on the 617s. I would suspect the relief valve on a 616 is set at the same pressure as the 617 if the part numbers for the replacement are the same.

It is obvious to me that if you own a 616 you should make sure the relief valve is discharging some fuel at idle. If not a simple fuel filter change might start the flow. Anyone driving a 616 with no overflow is putting their engine at risk besides other known issues..

It is kind of odd how this all started quite some time ago. An active member asked me why it always seemed to be the number one rod bearing that failed. Once past the current beliefs not making any sense to me. It just took on a life of it's own.

It was not easy in pursuing this area and posting would either produce either ridicule or some questions about my sanity. The first order of business was to decide what might be the cause. Fortunatly to some extent the vindication of my early thoughts has occured.

One last item for your consideration. When any given element is underloaded the first change will be a delay in the injector opening. This in my opinion is the primary factual issue with the power balance of the engine. That cylinder has had its timing retarded in comparison to another cylinders element that has loaded better.

No VO for me, heck I won't even run Bio!!

As for my mileage, the fuel quality here seems to be hit and miss, but, I am getting a consistent 28-29 MPG. I picked up a load of the old blue diesel and got just over 30.5 MPG once this summer.

This is one step in a process I have going. I'm building a custom IP with modified 10mm elements and I will be installing an electric boost pump back at the tank to feed the lift pump. Goal pressure will be 60 to 75 PSI at the out put of the lift pump.

The lift pump pressure does have an influence on the engine out put, as, if I open a bypass valve I have, (to make priming easer with the high relief pressure), the idle speed will drop about 100-150 RPM, and that is at idle.

I have a theory why higher pressure is beneficial, but haven't thought of a good way of tying everything together. That being said, I will attempt to lay the ground work as to the basis of the theory.

The element is like a syringe with a check valve, (the delivery valve), on the end and a hold in the side 3/4 of the way down from the top.

Now to start, the plunger is at the bottom, (bellow the fill hole in the side), and the syringe is full of fuel. When the plunger is pushed up, fuel will be expelled from the fill hole until the piston passes and seals the hole from the upper volume of fuel. At this point pressure is generated in the syringe, and fuel is forced out the check valve. The plunger continues to push out fuel until only 25% of the start volume remains in the syringe.

Here is where things get interesting, (well to me anyway), at this point there is a sealed chamber full of fuel, the only possible opening is the check valve which only lets fuel flow out, not in.

The plunger needs to go back down bellow the fill port to allow the syringe to be refilled for the next cycle, but, with a check valve blocking the only possible source that could be used to vent the syringe, allowing air to replace the area, (volume), created as the piston moves down in the sealed syringe, how will the piston be able to overcome the vacuum and move down?

I think what happens is that the pressure inside the syringe, (element), as the result of the vacuum that is created as the piston tries to move down, is that the pressure inside the element drops to a point where the remaining fuel in the element actually boils, (the result of a high vacuum), expanding in volume, which allows the piston to move down. Now once the fill port is opened, the pressure in the element needs to be restored to at or above atmospheric pressure to condense the boiled fuel and fill the element.

I can see how the base fuel pressure can have a big effect on quickly the pressure is restored in the element let alone the filling of the element at high speeds.

There is more to this, but lets see what everyone thinks of this nugget of thought.