fuel pressure

[OM616]

Originally Posted by barry123400

. I have to hope your car has plugs that do not have squiggly wires between the glow plugs. If so the test is not practical. If the engine does not have the series plugs. Used before 1980 I believe. We are good.

My 240 is a 78 with the loop style plugs. I am planning on up grading to the pencil type when I make new Prechambers for it, long story in a different thread.

I intend to build a calibration, for lack of a better term, tool that will measure the mv output at specific temperatures for my prechamber project. The effort is to compare the consistency between individual GPs as well as the consistency of the out put of an individual plug over time and glow cycles.

If the individual plugs will hold a reasonable repetitive tolerance, a scale can be generated for each plug to convert the mv reading to an actual temperature. If individual plugs will not repeat with in a reasonable range of predictability, as others have suggested, then alternative methods should be perused.

I have found that using a laser temp gun on the exhaust manifold, at the port, will show reasonably quick changes in individual cylinder exhaust temps. I have found that my #1 runs the coolest 2&3 are the same and #4 is the hottest. I assume the location and temperatures are connected. 1 is alone at the front where 4 is getting all the heat from the other 3.

I had to back off the fuel to #1 by turning the delivery holder to eliminate a ruff idle. (it was working harder than the other three) I also ended up shimming up the #1 barrel about .010 to get it to stop nailing all the time.

Machine parts rarely wear at equal rates and in the case of the IP unequal wear can have a profound affect.

[OM616]

Originally Posted by ForcedInduction

Tell that to my lift pump as it peggs my 30psi gauge.

I would tell your pump that I was not talking to it as it is on a 617. I am speaking of my 616 lift pump, if there is a difference. The specks that I posted came from the new lift pump. I would be thrilled to not have to screw around to get my fuel pressure where I want it.

What is the part number for your lift pump? Is it different from that for a 616?

[Graminal95]

I have a stock rear end of 3.69, and that day was driving around VT with an average speed of ~ 45mph.

I did just do 2 tanks of fuel with a combined mpg of 36.3! That was a lot of highway at ~65mph. I think I might be getting summer diesel soon and that should give me more consistent mid 30's mpg. Yay 261 nozzles and a turbo.

The MB manual only states min. pressures, so I guess as long as your above that you should be OK.

Forced what are you using for a pressure reg.?

[QUOTE=OM616;2158274I would tell your pump that I was not talking to it as it is on a 617. I am speaking of my 616 lift pump, if there is a difference. [/QUOTE]

There isn't.

[barry123400]

[QUOTE=OM616;2158250]My 240 is a 78 with the loop style plugs. I am planning on up grading to the pencil type when I make new Prechambers for it, long story in a different thread.

Your overall post was interesting. Apparently you are applying alot of thought to things. Sorry to hear you have the series plugs at the moment.

One of my cars the 77 300d still has them and they seem to work well. Or at least well enough I have no reason to change them out.

I tend not to use my old diesels in the cold and salt up here. That alone helps those glow plugs seem adaquate as well I suppose.

Best of luck with your projects. They do sound interesting. Allow as well I did not know you had good systems knowledge when I addressed my questions to you..


At some point I hope to at least do some testing as soon as time frees up a bit myself.

[Doktor Bert]

So, have we arrived at a good increased lift pump pressure??? I read of a spring in a previous post that will increase the pressure.

What is the factory recommendation (in psi) for lift pump output???...Robert

[OM616]

Originally Posted by ForcedInduction

There isn't.

Then you have got a strong pump

[Number_Cruncher]

Back in another thread, Yellit posted some spring data and with the piston area, it worked out at a similar *maximum* delivery pressure from these pumps. So, 25 to 30 psi sounds about right.

All that's really necessary is that the lift pump can overcome the pressure of the IP relief valve, and maintain some return flow to cool the pump.

As the injector pump itself traps a known volume of fuel (depending upon element rotation), then, the filling pressure is not *too* important. If the filling pressure is zero!, then, yes, you might have problems with cavitation, and less than full delivery, but I would be seriously surprised to find that any significant difference between an IP relief valve set at 10psi, and one at 15psi.

[Doktor Bert]

And are we checking lift pump pressure between the filter and the IP, or, are we checking between the lift pump and the filter???

What's the factory spec in psi???...Robert

[Doktor Bert]

Originally Posted by OM616

The spring that came in the new lift pump generated about 13 lbs of force just before coil bind which is @.900".

The free length of the spring is 2.450" and the installed height of the spring is 1.425"+-. The witness marks on my old pump suggests a piston travel of .250"+-.

The piston dia is .865 (measured quickly with calipers) and has an area of about .587 sqin.

If we were to say the area was .500 sqin for simplicity, and if the spring was at coil bind, the most pressure the pump could make would be 26 psi.

The spring I am getting has a free length of 2.5" and a rate of 25Lb per inch rate. It will be able to generate the pressures I want and will be able to keep better contact with the cam at high speeds.

Can you tell me more about this spring??? Dad wants to experiment on his 617.952 and I thought I could post results...Robert

[OM616]

Originally Posted by Doktor Bert

Can you tell me more about this spring??? Dad wants to experiment on his 617.952 and I thought I could post results...Robert

It is important to note that I selected this spring due to its specks, not because it is optional MB lift pump spring.

I ordered the spring today to put in my turned up 616 IP. I have not put a gauge on my 617.952 yet to see what it puts out.

I ordered it from Century Spring. www.centuryspring.com
the stock # for the spring I ordered is 72065. Price was $8.04 ea.

I have thought of putting an fuel pressure accumulator in the line in an effort to reduce the pulsed frequency of a piston supplied, hydraulic system. I decided last night that I will build one.

My goal is to have 20 lbs of consistent fuel pressure regardless of load and speed.

[Number_Cruncher]

>>My goal is to have 20 lbs of consistent fuel pressure regardless of load and speed.

Sounds like fun fun, but, why do you think it's important?

I'm not sure what you would gain over a correctly working standard fuel delivery system. When the fuel pump is working against a good IP relief valve, the pressure should already be consistent enough.

[barry123400]

At this stage one may not really want to really moderate the pressure until the fuel supply method at a rebuilders is known. They might calibrate this pump somehow to normal pulses and declining pressure etc that normally occur. Originating from the cars lift pump.

In fact with the lift pump sent in with the injection pump I really suspect it is utilized for calabration Thats once it is determined it is in good condition.

I would ask a pump guy about what is used to power the pump feed fuel for calibration. Thats before installing any type of accumulator that could average pressure etc.

This would be typical of an accumulator with a retained air space. incorporated into the design.

. Someone a few posts back really jarred my memory as well. Under low pressure conditions cooling of the pump is less. The overflow return has to be far less or nonexistant.

The nice gentleman (with the loop plugs totally restricting his return line with a valve. Might want to read his pump temperature after a good run with and without the valve closed. The pump may or may not be heating.

[whunter]

Part of the injection pump design/engineering uses the excess, bypass fuel as cooling fluid...

[OM616]

Originally Posted by barry123400

The nice gentleman (with the loop plugs totally restricting his return line with a valve. Might want to read his pump temperature after a good run with and without the valve closed. The pump may or may not be heating.

I took my temp gun along with me on a 200+ mile run up north last summer. After running for 2 hrs at 70 mph the IP was the same temp engine oil flowing through it.

Graminal95 and I have our pumps turned up from what the factory set them plus they are have seen several miles of operation and many gallons of fuel.

We both seem to be loosing fuel pressure under load. If my goal is to get as much fuel in to the element at 4000 rpm to maintain start of injection timing and quantity, then I do not want to see my pressure drop. if anything I would want the supply pressure to go up.

I am plan on putting a turbo on my 616 after reading about Graminal95's set up, but I then I would turn up my pump even more, and if I am having a pressure loss issue now, it could get worse.

I am ok with the reality being that it dose not make any difference other than the gauge reads was I want it to.