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  #16  
Old 04-01-2009, 11:05 PM
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Originally Posted by Brian Carlton View Post
I'm not in agreement with the above.........or I don't understand it fully.

The elements in the IP must fill with fuel in a very short time interval. The rate of fill must be governed by the fuel pump pressure from the supply. At lower fuel pump pressure, the rate of fill must be reduced and the available power must be reduced.

There is definitely a lower limit whereby the fuel pressure will affect the power produced by the engine.
Not trying to be argumentative. I'm just relaying what my two sources, both quite reputable, shared with me. Again, I think it is a lack of volume, not pressure that creates problems...Robert
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  #17  
Old 04-01-2009, 11:06 PM
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Interesting posts. My theory on the in line pumps and effects caused by substandard base injector pump pressure on these older mercedes where slowly developed by obsevation of reports of members over time. And considerable thought.

This needless to say does not make them right of course yet evidence still seemed to build over time. First issue that the pump element loading is not influenced much by base pressure.

Your sources may be in error as there seems to be a really a pronounced effect. These pumps start to starve out at low pressure. I personally believe it is a selective type of starvation yet still open to other viewpoints. What is not open basically is that starvation does not occur at low pressure. Actually things that are far worse occur as well.

On many of these pumps the owners just increasing the relief pressure. This of course increasing the base pressure if everything is well really improved the cars performance substantually. Many posted cases. In fact I originally independantly developed the ideal it would probably work based on other observations. Remember all that was done was to increase the base pressure from what it was. What scared me was at first the people were not finding the starting pressure nor terminal pressure after the adjustment. So pump element timing advanced further than desirable was a possibility. The elements where loading heavier. Remember I did not want to see damages. Althought the higher end was limited by the ability of the lift pump to deliver plus some other factors.

The people had simply stretched the springs in the return relief valve to increase the release pressure. Again absolutly no pressure gauge was used in the vast majority of cases. So little knowledge was gained. Still for some of these cars it was like night and day. From turtles to almost tigers for comparison. I really anticipated it might be good. For some it well exceeded my expectations. For those that saw no improvement a pressure gauge would have answered why.

For good end results during a rebuild it is common to increase the base relief pressure on these pumps by some rebuilders even. At least favoring the top end of the allowable range. If a pump builder is not aware of this I can only hope he never rebuilds one of my pumps.

It seems to appear in some way a higher pressure than lower pressure loads the elements better and more equally. Even possibly some more than others or a sporatic type loading occurs in otherwords at very low pressure. Rather than list song and verse further as it is a very long explanation. The elements of these pumps are basically fed by a lift pump that retains pressure but loads itself fundementally once per injection pumps total revolution. If low pressure problems are present I assume only the number one element sees much assistance at loading . Or the majority of what limited assistance is available. Thus element loading effort is decreased as each additional element is loaded in sequence.
The result is the number one injector element sprays a greater quantity of fuel. The next element perhaps slightly less and slightly delayed or retarded because of the lower quantity loaded. So that cylinder is displaced power stroke wise a small degree. This condition is progressivly worse as each further element is sequentially loaded.

Remember as well that even though there is a lift pump designed to retain and provide a constant pressure out put normally in conjunction with the relief valve on the injection pump. The pressure is still not static in the pumps even when everything is working properly. From the time the first element loads till the last one in the sequence. The base pressure in the pump has swung downward.

Now the hurtful part for these guys in the pump buisiness. Especially that think the base pressure on these pumps is basically irrelavant. These pumps are calibrated along that falling pressure curve. . It is partially established or point of origin of the declining pressure curve is established by the pressure present at that relief valve initially.

The pump maker wants that checked before any calibration is attempted. Lower the base pressure enough and the pressure curve becomes impossibly different. Since the base pressure curve does not go negative in relation to zero pressure the curve flatlines as soon as pressure approaches zero. At this point by calibration elements are loading very poorly. They were calibrated for a feed curve that no longer exists. All kinds of effects like individual cylinders being retarded occur. Progressivly worse as the distance of sequence from the lift pump being charged up is engaged.

All I can assure you of right now is regardless of what the pump guys stated. The amount of base pressure in these pumps has a real effect. The more serious implications will have to wait for later. There are many. It is almost certain that the number one rod bearing failures so common on these engines are a direct result of low fuel pressure in the base of these pumps over a long time span. Simply put under low base pressure the number one cylinder gets the most advanced timing and perhaps a little more fuel than any other cylinder. If it actually sprays more is unknown to me but the timing is better and advanced more than those that follow at least. I think since the number one rod bearing carries more than its share of the work constantly under those conditions the rod bearing just wears out faster than the others.

I guess that being told by pump guys that the base fuel pressure does not matter really blindsided me. If there is one thing that is absolutly certain it is that the base pressure does really matter in a substantial way. On these inline piston pumps anyways.

It was like standing on the moon and all of a sudden someone saying the earth does not exist as a general analogy.

Last edited by barry123400; 04-01-2009 at 11:15 PM.
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  #18  
Old 04-01-2009, 11:07 PM
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Originally Posted by winmutt View Post
Yes. I never even considered using the tach signal as a method to measure timing but it is certainly with the right hardware. I have an arduino board which should certain be fast enough to measure timing with. Hopefully by the end of the summer I will have more time to tinker with this. As you can see in the link I want to use the GP's as a thermocouple. Using the tach sensor as a pick up to determine crank position is simply fantastic when combined with actual ignition in the cylinder.
I think your methodology has merit...Robert
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  #19  
Old 04-01-2009, 11:14 PM
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Originally Posted by barry123400 View Post
"It was like standing on the moon and all of a sudden someone saying the earth does not exist as a general analogy..."
Barry,

I am not contesting your findings. Instead, I would only suggest that some method of watching timing while decreasing lift pump pressure be performed to verify an effect on timing. I would also suggest that you reduce the volume, by means of a inlet restrictor and record the changes.

I was surprised by what the two Bosch shops shared with me today, but it simply re-enforced the theory that you can have pressure within limits and not enough volume of fuel available.

I do think some testing is in order...Robert
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  #20  
Old 04-01-2009, 11:16 PM
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Originally Posted by Doktor Bert View Post
Not trying to be argumentative. I'm just relaying what my two sources, both quite reputable, shared with me. Again, I think it is a lack of volume, not pressure that creates problems...Robert
The lack of pressure will result in a lack of volume...........
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  #21  
Old 04-01-2009, 11:18 PM
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Originally Posted by barry123400 View Post
"I guess that being told by pump guys that the base fuel pressure does not matter really blindsided me. If there is one thing that is absolutly certain it is that the base pressure does really matter in a substantial way. On these inline piston pumps anyways..."
You can have adequate pressure without adequate volume. A dirty fuel filter reduces volume in any hydraulic system, but pressure and volume can often be totally different.

I agree with you, buut I think far too much emphasis is being placed on pressure and not enough on volume. I can restrict any circuit in a hydraulic system and create pressure, but it won't have sufficient volume...Robert
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  #22  
Old 04-01-2009, 11:18 PM
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Originally Posted by barry123400 View Post
I

If there is one thing that is absolutly certain it is that the base pressure does really matter in a substantial way. On these inline piston pumps anyways.

It was like standing on the moon and all of a sudden someone saying the earth does not exist as a general analogy.

Agreed. The statement cannot be entirely correct. Base pressure may not be relevant above a specific point. Sufficient fuel is available at or above that point. However, with a weak pump and fuel pressure below the specific point............the volume available will be reduced and the engine won't develop full power.
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  #23  
Old 04-01-2009, 11:20 PM
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Originally Posted by Brian Carlton View Post
The lack of pressure will result in a lack of volume...........
Not in every case, Brian and any hydraulic shop will tell you this. A lack of pressure is often the result of a lack of volume. My point is, look deeper into the issue and see if there isn't something contributing to the low lift pump pressure/volume that a new lift pump could be masking.

I am not arguing with any of you, merely suggesting a wholistic and analytical approach...Robert
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  #24  
Old 04-01-2009, 11:22 PM
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Originally Posted by Doktor Bert View Post
You can have adequate pressure without adequate volume.
In a flowing system, you cannot have adequate pressure without adequate volume. If the pressure is reduced, the volume is reduced. A clogged fuel filter will reduce volume..........and you'll find that the pressure is also reduced.

In a static system, you can have whatever pressure you wish......because there is no volume (nothing flowing).
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  #25  
Old 04-01-2009, 11:22 PM
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Originally Posted by Doktor Bert View Post
Interesting points....
........
Now, in the case of the GM 5.7 litre and 6.2 litre diesels, both using the Roosa-Master Rotary Injektion Pumps, they will produce the same delivery pressure regardless of the presence of a lift pump or even any degree of supply pressure. I have verified this on the test stand during calibration.

These IP's use a 6 to 7 psi supply from a mechanical fuel pump.
Robert, don't the Roosa/Stanadyne pumps have an internal vane-pump pressurizing the body to the 30psi range?

The similar Lucas/CAV certainly does.

With any kind of internal (positive displacement) transfer-pump, then of course a variation in external feed-pressure won't affect the internal body-pressure level significantly.

Also, earlier in the thread, someone said that regular diesel timing tools won't work on the 616/617. Why would that be? I've never tried to put my Snap-on "clamp-on-line" type timing meter on an MB, but I don't see why it wouldn't work just as well as it does on similar design IDI's like the Ford 6.9/7.3 that I use it on... ??

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WANT to BUY: 3.0L diesel engine.

My other diesel is a....

1962 Cat D9-19A, 2,000 cu-in TD
1961 Cat 966B, D333 TD, powershift
1985 Mack MS300P 8.8L TDI, intercooled, crane-truck
1991 F350 4x4 5spd 7.3 IDI NA
1988 Dodge D50 4x4 5spd 2.4 Mitsu TD
1961 Lister-Petter 14hp/6kw Marine Corp genset weekly charging 5400 lbs of forklift batt for the off-grid homestead.
1965 Perkins 4-108 Fire/water Pump
1960 Deutz 20hp/8kw genset
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  #26  
Old 04-01-2009, 11:23 PM
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Originally Posted by Doktor Bert View Post
A lack of pressure is often the result of a lack of volume.
A lack of volume is due to the lack of pressure. The two are interrelated..........and any shop that tells you otherwise doesn't understand the physics of the system.
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  #27  
Old 04-01-2009, 11:28 PM
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Richard,

I am not sure if that timing light arrangement would work. Not all Roosa-Masters have a vane pump, which is why the 6.2's had a mechanical pump driven off the camshaft.

Brian,

I would stil be interested to see if a timing change took place based on low lift pump volume/pressure. This is the point that I have seen in this thread and it is what I asked John and Gus specifically and their answer was emphatically that low inlet pressure will not change the delivery tiiming, providing the system is not aerated...Robert
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  #28  
Old 04-01-2009, 11:31 PM
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Originally Posted by Doktor Bert View Post
Brian,

I would stil be interested to see if a timing change took place based on low lift pump volume/pressure. This is the point that I have seen in this thread and it is what I asked John and Gus specifically and their answer was emphatically that low inlet pressure will not change the delivery tiiming, providing the system is not aerated...Robert
I don't see how the reduced fuel pressure would affect timing in any way. The timing is governed by the pressure developed by the pistons in the IP...........in similar manner to reducing the volume of fuel by backing out of the pedal...............the timing is unaffected by reduced fuel.
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  #29  
Old 04-01-2009, 11:36 PM
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Originally Posted by Brian Carlton View Post
A lack of volume is due to the lack of pressure. The two are interrelated..........and any shop that tells you otherwise doesn't understand the physics of the system.
Okay, Brian...I have a great deal of respect for you. I'll make this easy and just give up trying to assist in any way with the possibility that there could be another alternate cause for this questioned timing changed based on low lift pump pressure.

I will also concede that two authorized Bosch IP shops (Advanced Diesel Systems in Fresno and Pacific Fuel Injection in San Francsico) know absolutely nothing about the pumps that they calibrate for a living.

I will go even further to say that companies that build/service hydraulic systems for profit have no idea what they are doing, even when we have experienced high pressure, low volume problems in heavy equipment, due to a restriction in the system that was hard to find because line pressure (working) was within specification.

Lastly, I would suggest that the timing should be electronically monitored and fuel pressure and volume decreased to see if in fact there is a change in the IP timing.

I have nothing to gain here, Brian and I certainly don't want to upset or offend you. I try to contribute good thinsg to this forum and I always differentiate between what is my opinion, what is based on experience and I always cite my sources when offering technical advice.

I am very interested in the outcome of all this testing and I will contribute in any way that I can...Robert
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  #30  
Old 04-01-2009, 11:38 PM
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Originally Posted by Brian Carlton View Post
I don't see how the reduced fuel pressure would affect timing in any way. The timing is governed by the pressure developed by the pistons in the IP...........in similar manner to reducing the volume of fuel by backing out of the pedal...............the timing is unaffected by reduced fuel.
I tend to agree with your statement, Brian, but this question of a timing varience based on low lift pump pressure was posed early on in this thread and that is one of the points I was trying to address...Robert
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