No offense taken.

I simply wish to note that you cannot have a change in volume without a corresponding change in pressure in a flowing system.

Nothing will cause fuel to move from one point to another unless there is a pressure differential between the two points. The greater the pressure differential..........the higher the volume of fuel. If I want to double my volume of fuel.........I need to double the fuel pressure if I use the same system. Or, I can get a larger system............larger lines..........bigger fuel filter, etc., that will flow more fuel at a lower pressure.

The two are always related to each other.

Dr. Bert or Robert. I realy enjoy these forums. Especially the vast majority of people that use them. Not much I say or think is written in stone either.

I also agree that tests should be made to at least add numbers to things. The reason I try to stimulate others is my current lack of time. I keep hoping some window wil open up but have little hope.

The older I get the busier I seem to get. I try to make a contribution. Or at least try to instill people to think things though.

I have the equipment for many forms of testing on hand as it is used occasionally in some of my projects. Yes I did throw the tach sensor ideal out as I have always been looking for a way to dynamically check the timing. No time to develop it although should hopefully take very little. I never was especially fond of the vibration pickup. It is too hard to verify it's actual accuracy. Possibly built very sophisticated with selective filtering in spades. You might tend to trust it more.

The simplistic milli volt method did not cut it really either. Just too many variables.

Since you mentioned the tach sensor. A transparent insert for the glow plug and commonly available equipment could easily at long last make a very accurate dynamic timing check a reality. There are probably many ways to deal with it especially if by accident the sensor is precision located. Triggering the strobe with the flame front or a fast acting sensor could do it as well perhaps. There are other approaches that will occur with time.

I have not examined the device the gentleman is reffering to. I hope he triggers from the tach sensor and just uses a calibrated delay to compansate for the degrees off tdc. You might even just do the mathamatical calculation and keep it really simple. We will see.

I also want to explain the great difficulty I have had to figure out a way to increase the milage potential on these old indirect injection engines. For what seemed a frustrating long time nothing came to mind. Since I figured that this ground had been covered by mercedes engineers in depth I felt it would not be easy. . Now something has occured to me and I want to put the base pressure of the pump thing to rest. Or let others pursue it. There was never any black magic involved there anyways.

It was just an appeal to make people aware this area was signifigant enough that more attention should be addressed to it. From a certain point it would rectify itself. Just requires lots of posting by people that correct their pressure properly and install a monitoring gauge. The upside? Perhaps fewer engine failures will be experienced by members. Plus better fuel milage on some.Better power balance etc. as well.

We as members also hit a peak of about one engine a week being reported with a destroyed first cylinder rod bearing. Some member asked me a possible cause. That eventually led me to this point. Right or wrong.

I too would like to see the numbers as well though. The usual dificulty of no on board electronics makes it a challenge to develop some of them on these engines. The best option to get at least some of the numbers is to put one of these old pumps on a test stand and vary the feed pressure. It would at least verify the concepts well I believe.

Anyways I have decided to post soon an effect I observed years ago. If the reason it occurs can be established we just may find a way to apply it to these engines. I am not really optimistic.

On the otherhand if the effect occurs for reasons outside my current understanding. It might be applicable. That it is outside my current undertanding is a reasonable possibility as in ways it seems to defy logic. All I know for sure this effect does occur. Others on site may have noticed it as well. If so they should have paid attention. Of course I noticed it as well but forgot till reciently.

Might not pop point pressure be later in time if The elements loaded with a lesser volume?
Perhaps thats where the pump guys were quoting timing remains unless the fuel basically includes a percentage of air.This is something I had not considered previously.

The other component. It is reasonably understood the pressure does not remain constant during one pump cycle in the base. I think but am not sure where I read this. If this is so then a curve does exist.

It may even be some effect from the relief valve. It is a possibility if the manufacturer wants the pump calibated by the same feed method as in the car basically I imagine. If this was not so the manufacturer would not ask to have the tech check the relief valve pressure release point before calibration. I know it is a requirement from Yellit talking to his pump guy. Also it is considered benificial to set the relief valve to the high end of the range.

If the pressure is reduced enough this curve may change. The elements have been calibrated to a certain existing curve at the time of calibration. That curve is possibly different at low pressure. Even if the same profile is initially present it will tend to flatline if approaching zero pressure during the latter part of the pump cycle perhaps. Or if the dive goes through the zero pressure point then does the resultant short term negative pressure produce the air in the fuel.? Or can a underfilled element generate air when filling is inadaquate? Or a combination of the two perhaps. Where else could the air be coming from? Anyways indeed if air is present the applecart is really upset. There might still be some meeting of minds here. I really feel the pump guys could have given a more in depth explanaion.

Mr hunter also implied low fuel pressure will over time destroy the injection pump. His post wednesday relating to this area is on another thread.

Barry,

I don't think anything here is going on outside your current understanding. I am actually quite interested in all this discussion about lift pump pressure and performance. I can't remember ever having a bad lift pump, or perhaps, we just never looked closely enough???

I do not think that IP timing will change with a reduction in lift pump pressure. Both Bosch Service Centers told me this. However, I believe that low lift can deprive the pump of sufficient volume which 'leans' the fuel mixture and reduces power, increases piston crown temperature and ultimately, destroys the rod bearings.

Two things here could be checked; The first is timing when lift pump pressure is reduced and EGT at the same time. That would tell us a lot about what effect the lift pump potentially has on these engines.

Input anyone???...Robert

The IP is a device that regulates volume. When you press down on the pedal..........the volume is increased..........when you let off.........the volume is decreased.

If the timing were affected by pedal position..........we'd be in a heap of trouble.

I agree with the deprivation of volume with low pressure, as I've mentioned above.

However, there is no "lean" condition when discussing a diesel. The engine always runs with more air than it requires with the exception of maximum power. Any reduction in volume to the cylinders simply produces less power. It's no different than lifting your right foot.

In reality, I believe the piston crown temperature would be reduced as fuel is reduced.

I have no understanding of how the rod bearings could be destroyed with reduced fuel.

Brian,

I am glad that we can exchange dialouge on this like gentlemen. I am most interested in this lift pump issue and I have tried to share what information I can that might help us all, collectively, arrive at a proximate cause.

First of all, two reputable and licensed Bosch shops both told me bluntly that IP timing is not affected by lift pump pressure. On the other hand, respected forum members have found a performance improvement with an increase in lift pump pressure. This makes me curious as to what the volume of the lift pump output is.

My parents have friends up in the mountains with a larger citrus ranch. Dad and I have, for many years, tended to their heavy equipment on a seasonal basis. There was a certain skip-loader that wasn't working properly. We checked the hydraulic pressure on the offending circuit and it was 160 psi, right within specifications, yet the system was not working properly, even with constant pressure.

I called a local equipment shop who asked if I had checked the volume when I took a pressure reading. I told them I had not, since pressure and volume are inter-related, similar to your response to this thread. The gentlemen told me that my problem was a lack of volume, even with adequate pressure.

My first impulse was to tell him he knew nothing about physics, hydraulics, etc., but then I remembered the bumblebee that cannot fly. Dad and I proceeded to check the pump volume.

At 1800 rpm, pressure was at 160 psi, within specification, but the pump volume, which was supposed to be 5 gallons a minute, was only slightly over 3gallons. Impossible you say??? That was my response.

I went to the equipment shop and spoke to the gentleman I had spoken to previously in person. He told me this is a common problem in hydraulics and people overlook volume because they assume that if they have pressure, they have volume.

On his recommendation, we changed a spool valve and retested. The pressure stayed at 160 psi at 1800 rpm, but we now had almost 6 gpm of output, slightly above the specification. In this condition, the loader worked properly and I came away with a different point of view.

I shared this because I felt it was relevant...Robert

Brian,

I know that in a direct-injektion engine, in this case a Deutz Air Cooled Diesel, a plugged injektor will cause piston crown overheating and seizure. The piston is cooled by the fuel spray, even though it is a momentary event.

When I worked for Atlas-Copco in Fullerton, CA. in the 1980's, a factory representative of Deutz went to great lengths to explain this to me. Now, since the 617 has a pre-chamber and no fuel spray actually reaches the piston, I am not sure how this will correlate...Robert

I don't believe the two are mutually exclusive. The performance improvement was the result of the increased fuel volume.......caused by an increase in lift pump pressure..........not a timing change.

It's definitely relevant...........however, I must question the testing procedure simply because the data, as presented, violates physics.

If you test the system pressure ahead of the spool valve and find a pressure of 160 psi between the pump and the spool valve............and then test the system pressure after the spool valve...........I'm confident that you will not find the same pressure. If the spool valve was the limiting component in the system (the largest restriction), the pressure downstream of the valve will be reduced and the resulting volume that is delivered will be reduced.

All testing must be done with a fully operational and flowing system...........static pressures are not relevant.

I agree with you and therefore, both John with Advanced Diesel Systems in Fresno and Gus at Pacific Fuel Injection in San Francisco, are bothy correct when they stated that the IP timing will not be affected by supply pressure...Robert

Brian,

Now my question to you is this....What performance benefit can be obtained with an increase in lift pump volume??? How much can you increase lift pump volume before fuel economy suffers???

In my mind, the size of the fittings and tubing between the lift pump and the IP could be doubled, along with an increase in pressure and then the results recorded in both chassis dyno power output and EGT.

Thoughts???...Robert

All I can say to you is this....

After this event, we started testing volume and disregarded pressure. In this case, with a John Deere loader, the pressure, in the working system, remained at 160 psi before and after testing. However, the increase in available volume, from 3gpm to 6 gpm, brought the system back into operation.

I agree it may not make sense, but since that time, we have encountered this more than once.

I had hoped this might help our discussion, but I fear all I have done is muddy the waters...Robert

You need to think in terms of pressure...........the fuel pressure at the point of input to the barrels. How much fuel enters the barrel is strictly dependent on the fuel pressure at that point. If there is insufficient fuel pressure, the barrel won't completely fill and the engine won't make maximum power.

There is a specification whereby the barrel will completely fill..........I don't know it..........but, say that it's 10 psi. If the fuel pressure is 8 psi, the barrel won't fill completely. If the pressure is increased to 10 psi, the barrel will just fill completely and the engine will make full power.

However, if the pressure is increased to 12 psi, the barrel cannot overfill (a physical impossibility) and liquid fuel is, effectively, incompressible............so, the engine still gets the same amount of fuel as it did at 10 psi..........and it makes the same power.


In answer to your question..........you can have a huge pump with giant lines but it won't accomplish much if the limiting factor is the port into the barrel. If you increase the size of the port and the size of the barrel..........now you're talking.

I don't question the data...........I question the testing procedure.

Was the pressure measured between the pump and the spool valve under both conditions (before and after spool valve replacement)?

Actually, the timing *may* be affected by pedal position, depending on the design of the IP plungers. The injection start and end events are controlled by helixes on the plunger. When the pedal is depressed, the IP rack rotates the plunger and changes the relation of the helixes to the inlet and spill ports. Plungers with a lower helix have a constant start of injection timing and variable end of injection timing (the duration being proportional to delivery volume per stroke). Plungers with an upper helix have a variable start of injection (variable timing with pedal position) and constant end of injection. Plungers with both upper and lower helixes are also used. I do not know what style plunger is used in the various MB engines, but there is no reason to necessarily assume that there is not a variable start of injection with load (pedal position) as it can have a big influence on power, emissions, and noise.

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1987 W201 190D