DS4 pump mods

[buddy]

You got that right Matt, more pressure for same time is more flow than PCM knows. If someone figured out how to reliably regulate the pressure higher then it would be a pretty sweet modification.

DS4 will idle fine and cruise fine, but you wouldnt be doing this mod if you were concerned about driveability. Its also easy enough to change the fuel curve to desensitize the pedal. May be one of those things that needs to come with its own customized PCM program.

 

[Woody35]

very select few of commonrail cummins guys are using standalone computers due to the complexiety of the dodge computer and they report excellent results. that would almost certaintly be easier to control the pulse width. all it needs is a cranksensor and cam sensor i think. plus it can modify it's programs on the fly. the only problem is they are 8-10 grand. i dont think anyone can justify putting that much money into a 6.5

 

[buddy]

Yes when you can redefine all of the software boundries with a whole new software program you can do anything you want, but yeah, that takes a lot of time to learn or someone that makes big bucks to do it.

 

[6.2 turbo]

I would like to have my charge pressure somehow raise with boost pressure,maybe a fmu or a solenoid valve that closes when boost is built,this would help control the over fueling at low rpms and make the throttle more forgiving ,and less surging. If the metering valve is not perfect,cranking the charge pressure,will make it more noticeable,so I guess on the DS4 you would want a good fuel solenoid or needle,then it should be ok. Also I don't know how high pressure you can go with the DS4 ,aren't they already set to 148 psi ? It would take some testing,hopefully with a cheap core pump to see how high is ok,my problem with the DB2 is that I'm maxing the charge pump volume,since the pressure drops at full fuel,it might drop on the ds4 also.

 

[Matt Bachand]

Yes when you can redefine all of the software boundries with a whole new software program you can do anything you want, but yeah, that takes a lot of time to learn or someone that makes big bucks to do it.

Seems right up your alley though Buddy:thumbsup:

Go to Barnes and Noble and pick up a copy of "Assembly for Dummies!":scared1:

 

[6.2 turbo]

Does the computer send ground signals to the pmd which converts it to 12 volts for the fuel solenoid,so the pmd takes the heat instead of the computer?

 

[buddy]

Computer sends a digital pulse width signal to the PMD. It is a switching signal, so when PCM signal is high the PMD provides an analogue real valued signal to the fuel solenoid (metering valve). The PMD pulse is about 2V at idle and as RPMs increase its pulse to the FS increases up to 5V. Although the pulse width of the signal is the important part, and determines how long the valve is open. I think it increases in voltage just because it takes more power to switch it faster and faster. To increase RPMs the PCM will make pulse longer to put in more fuel and put pulses closer and closer together.

 

[buddy]

Seems right up your alley though Buddy:thumbsup:

Go to Barnes and Noble and pick up a copy of "Assembly for Dummies!":scared1:

I'm not that good, I understand it, but dont know it and dont have any other experience with Assembly language. I spent enough time with help just finding all these tables and constant in the program.

controlling that pressure with boost would be a great thing. Thats a better project

 

[Matt Bachand]

You would probably need the source code too I would think? I actually majored in Comp Sci but never did much assembly (if any) I don't even remember.... Different life ago...

I like your enthusiasm in the pressure / boost idea! Get to work!

 

[buddy]

You should be teaching us comp sci then. I only had a couple courses as part of my rocket science degree. And its a good thing a C is a passing grade :thumbsup:

All the code can be read on the chips. I could tell you anything you wanted to know about any OBD1 program just from a GMTDScanTech memory dump file.

 

[Matt Bachand]

What effect would putting a restrictor on the fuel return outlet on the IP have? Thinking it would keep higher pressure up to the pump perhaps, if it is more difficult to escape.

Question is, what effect would it do to the operation of the pump?

 

[schiker]

http://flashoffroad.com/Diesel/injectionpump/injectionpump.htm

-----------------------------------------------------
Injection Pump Housing Pressure
If the fuel return function in the injection pump becomes restricted and the internal pump housing pressure rises above the normal 10-12 psi, the injection timing will be affected. Housing pressure partially controls injection timing. More pressure retards timing, and less pressure advances injection timing. The engine will probably produce more white smoke due to lower combustion temperatures with a retarded timing. An incorrect housing pressure also interferes with the injection pump's ability to correctly meter fuel. Installing a "T" fitting in the injection pump fuel return line will allow you to test the return line pressure. The pressure should be below 12 psi. A higher reading would indicate a restricted fuel return line.

Injection Pump and Injectors
An injection pump with stuck or defective advance mechanisms can cause the engine to smoke abnormally. A timing test performed with an electronic timing set would help discover this problem. If you have a relatively low time pump and injectors, have them tested at a Stanadyne authorized re-manufacturing facility before considering replacement unless they are under warranty.
-------------------------------------------------------


This is how I think it works.....

The advanced piston is differentialized to the housing pressure. And I think housing pressure pushes back to retard timing from the stepper motor side pushing towards the PMD side. The transfer pump pressure advances timing and its pressure is a function of rpm since its a postitive displacement pump. It pushes from the PMD side towards the stepper motor. And I think the transfer pump is helped somewhat by the liftpump so it doesn't "slip or have pumping losses". For the timing to advance the transfer pump has to push more fuel into the advance ram mechanism and move the advance piston. In order for the advance piston to move it has to push out fuel from other side of ram into the housing and out the return mechanism. So less housing pressure would allow that to happen easier and advance timing easier. More housing pressure would make advancing the timing harder but should increase resistance to flow through and increase the transfer pump pressure (which is the charging pressure of the plungers).

The stepper motor does control the differentialized flow restriction through the advance piston and I suppose allows for corrections due to different fuel viscosities from different fuel temps/conditions ie cold start.

Looking at the return valve its just a dinky little spring/checkvalve mechanism. And i question just how accurate it is and if flowrate affects it much. Would a better regulated return pressure mechanism provide some performance gain ???

 

[Matt Bachand]

If you're feeding the IP 10psi 3/8ths inlet, or 5psi 3/8ths inlet, Is there an obvously large amount more fuel passing through the pump and out the return to the tank while supplying the IP with more fuel volume & pressure?

 

[schiker]

No maybe not significant difference in throughput if its working like it should.

The IP inlet feeds the transfer pump. The transfer pump then pumps the fuel through the IP. The transfer pump is a rotary vane pump and as such a positive displacement pump. Its flowrate will be a function of RPM. But I think the vanes can have pumping loss when the inlet is under vacuum. And I think it has pumping losses when the output is restricted depending on how much different than designed. So I think the LP can help the transfer pump but shouldn't push past it either.

But does the housing pressure vary as the return valve mechanism ages (spring memory sets) or from throttle changes wear the spring out from surges in throughput of fuel? Maybe the fuel viscosity drops due high temps or other reasons differences in lubicity etc age and varnish build up or ???? could affect the return breakthrough pressure.

 

[625fireman]

Possible dumb question here?????????????
If, could, one remove transfer pump and install an Air dog pump set at 100 -120 psi?????

maybe I'm not quite getting this completely, but my brain says it may improve fuel flow.

 

[Woody35]

Possible dumb question here?????????????
If, could, one remove transfer pump and install an Air dog pump set at 100 -120 psi?????

maybe I'm not quite getting this completely, but my brain says it may improve fuel flow.

i dont think the transfer pump is going to like fuel coming in at 100 psi but i wouldn't really know. the cp3 injection pump on a dmax can only take roughly like 15-20 psi before it can become damaged im pretty sure.

 

[6.2 turbo]

I often wanted to remove my charge pump and use a big Fass or Air Dog instead,this would mess with the timing unless the cam ring is locked. Or it could be externaly regulated some how.

 

[buddy]

You cant use an external unless you are just racing or something, because it uses the change in pressure to meter fuel correctly, because the pulse width was mapped to the expected pressure per RPM. This is on a DS4. The DS4 timing is controlled electronically, not mechanically like the DB2. So I would question the charge pumps advancing functionality. I can program it to be whatever timing I want at any RPM or fuel rate. At the same RPM and fuel rate I can have 8 degrees or 22 cam degrees advance.

 

[schiker]

Here is the transfer pump opened up. I suspect if the pumps compression chamber pressure "cylinder" of the rotary vane pump gets too high it leaks past the vanes and maybe distorts the white ring that holds the vanes out and spills backwards to the previous vane chamber then this chamber has to spill/leak more fluid backwards to the previous chamber and repeats back to inlet. Maybe when you increase LP pressure and flow the begining chamber has more pressure so the next chamber has more pressure and repeats forward such that the overall transfer pressure increases slightly. Another function of the white ring is to hold the vanes out. I think centrifugal force holds them out when running but during shut down depending on orientation they can fall down in slots. I believe this inner chamber can leak and is probably ported to housing pressure but I don't remeber it being ported directly I think it also is ported to the main shaft bearing etc. I'll have to look at that again.

Look closely at the vane / outer housing contact area. I don't believe the radius of the vanes matches exactly the inner diameter of the housing. A fluid pressure build up would act like a wedge and tend to push the vanes inward. I think this limits the transfer pumps output pressure.


The designed pressure differentials work in other areas too. And I don't understand all of them. One example is the stepper motor can't advance timing it doesn't pull on the advance piston it only pushes the spool valve. So hydraulic pressure differential to housing pressure physically moves timing the stepper motor just compensates and controls the pressure differential through movement of the spool valve.

 

[buddy]

Good stuff.

Since the DS4 has feedback from CPS and OS for timing, regardless of what the differential pressures are, the stepper motor can vary it to achieve the desired timing. Although, I'm sure there is a point at which it may not be able to compensate. With a mechanical DB2 it would all be only dependent on those differentials.

Does anyone know what timing the DB2 goes up to? Or how do you set the DB2 timing? Is it set to a specific crank degree, like 16 degrees?