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  #46  
Old 04-02-2009, 11:16 AM
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Quote:
Originally Posted by JonL View Post
. 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).
AFAIK, the Bosch pumps for the M/B are of this type, and have a constant start for the injection timing. I'm not familiar with the physics of the upper helix and how it affects timing.
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  #47  
Old 04-02-2009, 11:23 AM
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Originally Posted by Doktor Bert View Post
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
The Deutz engine probably uses the Mann wall distribution combustion system, where the fuel is intentionally sprayed directly onto the hot combustion bowl in the piston to aid in vaporization instead of relying on the atomization of fuel as it is sheared through the injector orifices or pintle. In the Mann system, a plugged injector would have an incorrect spray pattern, would not cool the piston, and would cause abnormal combustion that might further lead to piston overheating. If the injector were truly "plugged" to the point of not injecting fuel at all (which I don't think is really possible without something in the injection system breaking from the pressure) there would be no piston failure. No fuel = no combustion = very little heat.
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  #48  
Old 04-02-2009, 11:23 AM
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Even if it does affect timing the amount would be so miniscule, hundredths of a degree in relation to cam timing.
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  #49  
Old 04-02-2009, 11:27 AM
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Originally Posted by Doktor Bert View Post
I think your methodology has merit...Robert
Everyone @ STD has been saying that the GP are horrible thermocouplers. Why this is true I think they would give very accurate information, just not in relation to a fixed temperature scale. They should certainly help indicate timing per cylinder, graphed out the waves should be equidistant. I would really like to find a cheap alternative to the Bosch test bench. My biggest issue is measuring fuel quantity and duration. If I could do that there would be no need for the bench. One might be able to do most of the calibrations on the engine.
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  #50  
Old 04-02-2009, 11:41 AM
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Quote:
Originally Posted by Brian Carlton View Post
AFAIK, the Bosch pumps for the M/B are of this type, and have a constant start for the injection timing. I'm not familiar with the physics of the upper helix and how it affects timing.
The upper helix simply changes the height at which the inlet port closes depending on rack position, thus varying the start of injection with rack position. The lower helix changes the position at which the spill port opens depending on rack position, thus changing the end of injection with rack position.
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  #51  
Old 04-02-2009, 12:03 PM
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Guys I think the point that is being missed in this discussion is that the fuel system is over supplied with fuel and consequently has excess fuel returned to the tank. The pressure in the primary system is regulated by the restriction to flow by the injector pump and the internal design of the supply pump. Example if the fuel line between the supply pump leaks, the supply pump may not be able to reach specified pressure because of excessive flow.

Now say for instance the supply pump is designed to supply 6 GPM at 10 PSI to the injector pump. Now the injector pump can only use 3 GPM at WOT. If the pressure dropped coming from the supply pump to the injector pump due to a restriction somewhere maybe the pickup or intake side of the supply pump, it can now only supply 4 GPM. That is still more than the injector pump can use so the supply pump will still build 10 PSI. Now however, a lesser amount is returned to the tank from the filter housing.

By the same token, if the supply pump can only supply 3 GMP the injector pump is still getting its needed amount and the supply pump can still build pressure to 10 PSI. It will still run properly.

The issue that comes into play is when the supply volume is below needed amount then the supply pump cannot raise the pressure to its max specified amount. Say it only can pump 2 GPM due to a clogged tank sock. The engine will lack power and the max pump pressure cannot be reached.

In the Bosch pump timing is controlled by RPM so the timing will not be affected except that the enging will not rev as well due to starvation.

Someone brought in the standyne pumps. These are distributor type pumps. They have vane type transfer pumps internally. This produces a regulated pressure that varies with rpm. The pressure from this transfer pump not only supplies the distributor and consequently the injectors, but also pressures the advance piston. On the other side of the advance piston is housing pressure which is regulated by the return fuel fitting in the top of the pump. This housing pressure fixed at 12 to 14 PSI regardless of RPM. So as the engine accelerates the transfer pump pressure increases and moves the advance piston to advance the timing.

HTH clarify. I think you are all a great group and are really trying to get a handle on how these work. Keep up the good work.
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  #52  
Old 04-02-2009, 12:12 PM
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I think there is one more reason why gallery pressure may affect injection performance, and that is cavitation. Even if the supply pump provides sufficient volume to satisfy the injection pumps maximum delivery, if it cannot maintain sufficient pressure in the gallery the plungers may cavitate. The pressure in the gallery must be sufficient to fill the plungers quickly through the very small inlet ports while maintaining sufficient pressure within the plunger to prevent cavitation during filling.
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  #53  
Old 04-02-2009, 01:39 PM
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Quote:
Originally Posted by JonL View Post
I think there is one more reason why gallery pressure may affect injection performance, and that is cavitation. Even if the supply pump provides sufficient volume to satisfy the injection pumps maximum delivery, if it cannot maintain sufficient pressure in the gallery the plungers may cavitate. The pressure in the gallery must be sufficient to fill the plungers quickly through the very small inlet ports while maintaining sufficient pressure within the plunger to prevent cavitation during filling.
My experience with this is that in 5 years working in a Fuel Injection shop I have never witnessed any cavitation inside of a Element/Plunger and Barrel on any make of inline IP.

Cavitation is a result of the pressure and more specific the pressure waves created by the begining and ending of injection.

If your Delivery Valve is funcitong properly it closes and isolates the Plunger and Barrel from there end of Injection Pressure Wave coming back to the IP.

I have seen cavitation on all of the parts past and including the Delivery valve seating area and all the way to the Injector itself. It is also one of the reasons Fuel Injection Hard lines develop pin holes.

The other place that I have read there can be cavitation in an inline IP is the IP housing opposite the fuel inlet holes in the Plunger and Barrels.

After filling the plunger rises shooting a stream fuel out of the fuel inlet hole at a high velocity until the fuel inlet hole is closed off at begin of injection.
The high velocity stream of fuel can erode/cavitate the Aluminum IP housing.

Some makes of IPs have Steel Plugs across from the Plunger and Barrel inlet hole so that the high velocity fuel is deflected on the harder steel plugs.
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  #54  
Old 09-09-2011, 09:12 PM
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I realize this is a really old thread, but I wanted to find out if you all found out if increasing injection timing helped MPG's and didn't contribute to component failure?







..
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  #55  
Old 02-09-2012, 03:04 AM
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Originally Posted by Doktor Bert View Post
I still maintain that reducing lift pump volume, while electronically monitoring timing, would be worthy experiment, even though two Bosch service centers have told me lift pump pressure will not affect high pressure delivery in a properly functioning injektor pump...Robert
Well I sort of conducted this experiment on a 300sd. I took it for a drive and had never driven this car before and drove it a mile, came back to the house and happend to look in the mirror. I noticed a large trail of fluid following me as I pulled into the driveway. I popped the hood and saw a large amount of fuel exiting the fuel filter around the gasket in almost 360 degrees! It was running almost normal just down a bit on power. I felt the filter and it would rock on the threads and it was so loose it was not even close to the filter seal. The filter was hanging by the bolt! It still ran to the point where if I had not seen the fuel trail I would have not known anything was wrong in the short drive. The pump must be able to scavange fuel with little pressure.
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  #56  
Old 02-09-2012, 07:38 PM
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This is an old thread. I have picked up a little here and a little there over the elapsed time since this thread originated.

Some of my thoughts have changed to some degree. What I missed back then and may be of signifigant importance is the high pressure spikes released by the element barrels when loading and the elements pistons coming back down to reload. . It is going to be harder to load uniformaly with little to no fuel pressure assisting the new fuel into the elements. If the supply curve is seriously off the condition will be still even worse.

The only way to really know your current status is to install a fuel pressure gauge or at least check it with a gauge. I am even more certain that it is low base fuel pressure that is the principal culprit in the number one rod bearing issues then I was back then.

It simply just wears them out faster as they are saddled with a greater percentage of the work load. The power balance of the engine is disturbed with low fuel pressure to the base.

A requirement that flies in the face of fuel pressure being of no signifigance. The person calibrating the injection pump must make sure the relief valve is in the right area for pressure relief. If it is overflowing in that condition the lift pump is putting out adaquate pressure and volume.

Under those conditions the injection pump can be properly calibrated. To calibrate the injection pump without those requirements being met the calibration is then wrong. Or the pump is then being calibrated to standards that are not what the injection pump manufacturer wanted done.

So when you operate the injection pump at lower than calibrated pressure the calibration will be different than what it was set at. Also if one element is underloaded compared to another further away in the sequence it in effect is also unloading at the injector later that the designers of the injection pump intended.

That is effectively retarding the timing of the injector fed by it. When operating below the overflow recommmended pressure of the relief valve with partially obstructed fuel filters or a weak lift pump for example. The high pressure spikes from the fueling elements are not moderated by the cigar hose as much. Further disrupting things to some extent.

Plus the constant fuel pressure in the injection pump enabled by the relief overflow valve is replaced with a higher pressure initially falling off during the period of the overall lift pump cycle.

It just in general is not either a good ideal or good practice to be running with low fuel pressure in the base of the injection pump. There is no doubt the engine will run though. The manufacturer really wants to see about fourteen pounds and nineteen pounds seems to be better at idle.

All the last posters experience really proved is that he may have inadaquate base fuel pressure in his injection pump.Or it may be good. The only way to really know is to get a meter reading on it.

In many cases it will mean spending less than twenty dollars now or replacing the engine later. Many go the engine replacing route. It takes quite a long time to wear the bearing down. You just in all too many cases are unaware of how much wear has already accumulated before you got the car because of low fuel pressure if it exists. These engines are so noisy one can easily miss the early light knocking of excessive bearing clearance. If wear is present you do not eliminate it with correct fuel pressure. You do take the excess load that that number the number one cylinder has been subject away though. So the future wear should be at a much reduced rate.

If youi buy a 240d with a 616 engine. Finding the fuel pressure very low. I would pull the lower oil pan and plastigauge the number one rod bearing as a preventative measure. You do not know how long that engine was used with low fuel pressure. Long enough and you may find the bearing has excess clearance and should be changed.

Last edited by barry123400; 02-09-2012 at 07:56 PM.
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  #57  
Old 02-09-2012, 10:15 PM
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Originally Posted by Josh8loop View Post
I realize this is a really old thread, but I wanted to find out if you all found out if increasing injection timing helped MPG's and didn't contribute to component failure?







..
I started this thread but do not keep track of my Mileage. I am happy if my Car is working and drivable.
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  #58  
Old 09-26-2012, 10:16 PM
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Hello, found this thread in a search and have a couple questions: Which component on the OM617 is referred to as the "lift pump"? The entire IP? If not, can someone describe it, or even better, post a picture?

Secondly, how exactly would someone measure the working pressure that is mentioned on this thread? Where are you fitting a gauge? TIA.
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  #59  
Old 09-27-2012, 12:24 AM
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Originally Posted by treetrimmer View Post
Hello, found this thread in a search and have a couple questions: Which component on the OM617 is referred to as the "lift pump"? The entire IP? If not, can someone describe it, or even better, post a picture?

Secondly, how exactly would someone measure the working pressure that is mentioned on this thread? Where are you fitting a gauge? TIA.
To find the Fuel Supply/Lift Pump locate the Plastic (Primary) Fuel Filter and trace it towards the Fuel Injection Pump. It is made of Cast Iron and has the Hand Primer Screwed into it and it has a hard Plastic Fuel line that goes from the Fuel Supply/Lift Pump to the Spin-on (Secondary) Filter Housing.
The Fuel Supply/Lift Pump is bolted onto the Fuel Injection Pump with either 3 or 2 little Nuts; Depending on the model of Fuel Injection Pumpu you have.

You would need to make a fitting to check the Fuel Supply/Lift Pump pressure. It would be best to find a DIY on it.
DIY Repair Links
http://www.peachparts.com/shopforum/forumdisplay.php?f=82
http://www.peachparts.com/Wikka/DoItYourSelf

Also when the Fuel Supply/Lift Pump is working properly the pressure is controled by the Pressure Relief/Overflow Valve. The Valve is on the Engine side of the Fuel Injection Pump and is a Bolt that goes through the Banjo Fitting of the Hard Plastic Fuel Return line.

Long Fuel Pressure Relief Valve/Overflow Valve Thread
http://www.peachparts.com/shopforum/showthread.php?t=234609
Another from hunter
Fuel injection pump starvation with a good lift pump
http://www.peachparts.com/shopforum/diesel-discussion/247039-fuel-injection-pump-starvation-good-lift-pump.html
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