DS4 max fuel rates at X rpm

[buddy]

the IP's return line fitting is a 5psi regulator I think, or maybe its 12, but thats whats need to maintain 5psi on the input side.

 

[schiker]

I'll have to look again but I am thinking fuel is on both sides of the metering mechanism. As such relative to the housing pressure the mechanism sees the same force to close????. I remembered Diesel lubricates the solenoid plunger too so does the housing pressure really affect the closing force of the solenoid plunger? Maybe its a dymanic issue? Within reason say less than 60 ish psi I am thinking for the DS pumps housing pressure might only cause issue with seals/gaskets etc.

I think if you block off a return line on a DB pump it will stall the engine relatively soon as housing pressure does influence timing I think. Not sure what happens to a DS pump.

 

[6.2 turbo]

Housing pressure on the db2 is not related at all to lift pump pressure, I'm running 150 psi max charge pressure and about 12 psi lift pump pressure , and zero housing pressure.

 

[schiker]

I am not saying the lift pump pressurizes the housing. The transfer pump does that I think. But there is a relief check valve mechanism in the bottom of the inlet fitting to allow some kind of over feed or excess recirrculation back to the inlet from the rotor/distributor/plunger fill & pump (which would back feed the lift pump supply and also supply the transfer pump again too if it trips open).

Can you explain that some I don't know much of anything about the DB pumps.
Does the zero housing pressure advance timing or do anything on the DB? What is normal and or why do you run 0. What do you mean by 150psi charge pressure?

 

[6.2 turbo]

Sounds like you have it right. On the db2 pump charge pressure is created by the transfer pump,it moves the advance piston ,and fills the plungers when you open the throttle, I didn't think housing pressure was necesary so I deleted the solenoid and have a open return fitting, this will advance timing, normal pressure is very low, I would guess no more than 5 psi, I had a return line clog already and it messed the timing all up. I don't think you will gain advance on the ds4 by changing housing pressure. Checking charge pressure would be a good idea, 150 is not considered a safe number for the db2.

 

[schiker]

Correction to post 57/58.

Watch Bison's thread on DS IP mechanical rebuild.

http://www.thetruckstop.us/forum/showthread.php?t=21893

See post 8.

Hydaulic pressue does influence cam ring time somehow on a DS IP too somehow??? But stepper motor seems to help control the hydualic pressure so there is some type interaction???? Probably not as purely mechanical as DB pump and more electronic correction but still influenceable by mechanical issues.

 

[schiker]

My interpretation:....

It does have a hydaulic action/mechanism. The transfer pump feeds the advance piston which has "spool valve" ??? internal that adjust pressure flow through the advance piston and controls the ram pressure. It can vent off pressure to the housing too I guess depending on spool valve position. There would be a differential of transfer pump pressure to the housing pressure that could be controlled to provide ram pressure for the advance piston. Too much housing pressure would require more pressure from the transfer pump robbing charge pressure for plunger fill.

I missed the hydaulic action and interpretted it as porting for a flush of diesel to lubricate the mechanism. The stepper motor controls the "spool valve". I thought the stepper controlled time and was spring loaded to soften the load on the stepper motor and mechanisms. But now see the stepper motor just adjusts and corrects the piston pressure. The encoder and optic sensor would provide feedback for correction needed maybe.

Bison's thread mentions its a reed valve but I have never looked at what exactly a reed valve is or looks like. So some of my terminology may be off.

Left to right top to bottom:

Red straw shows fuel flow path where seen.
Pic 1 shows feed from transfer pump pressure in the distributor.
Pic 2 just ports leading to the advance piston from the banjo screw (pic 1 bottom of IP far right, the middle screw port if for assembly of rod that connects cam ring to advance piston, Left screw is for something else didn't go back to look).
Pic 3. is flow into the advance piston.
Pic 4. Spool valve internal to the advance piston. the 3 holes lead to spool sections and determine flow to piston pressure area or path to housing cavity.
Pic5 the advance piston
Pic 6. The exit to the housing cavity (under the cam ring)

 

[schiker]

The stepper motor controls the "spool valve" and the pressure in the advance piston ram.

Pic 1. advance piston. There are several holes and ports not exactly sure exact flow path or how but seems to allow flow to ram end that would act like a hydraulic ram or towards housing cavity. The spool valve is hollow red straw and there is a port with allen wrench sticking out. The red gasket would seal the end offand that cavity would make the hydaulic ram cavity or piston face.

Pic 2. The piston end where the stepper motor attaches and the "hydaulic ram cavity".

Pic 3. The "flapper from the stepper motor mechanism.

Pic 4. The stepper motor and flapper somewhat in place.

 

[schiker]

Now purely conjecture - speculation and up for discussion:

If the tranfer pump pressure is down due to high fuel rates (weak LP or dirty filter) and the timing needs to be advanced. Would the slight loss of charge pressure to increase advance piston force cause slight fluctuations in timing and different charge fills due to pressure fluctuations ??????

I know the camring is encoded and measured and should code if out of time but does stuff happen on the fly that doesn't always code????

This IP the advance piston is pretty scuffed or has some discolorization as the advance piston continually moves to correct time for RPM right. Could this wear cause leakage and piston pressure to fluctuate more. Could this compound /snowball and tend to cause fishbite ??? This IP was reported to have some timing and fishbite issues.

Just another reason to make sure good IP feed of fuel and fuel quality (viscosity and lubricity).

 

[Matt Bachand]

I would think when all things are equal for that split second you can feel it. Probably a reported fishbite which may not be noticeable anymore when pressure goes negative.

Advancement may be based on pedal position also to a degree, so it may advance for a called amount of fuel, but when supply can't meet that requirement it is now too advanced for the - slight second- where pressure is all synced up. Fishbite.


Also at that critical time of pressure change any leaks now turn to air getting sucked in, also causes fishbite.

 

[ak diesel driver]

on my IP which has advance problems when cold. I can hear the advance change up and down up and down until the IP warms up. If I throttle it it will stop it's oscillation.

 

[schiker]

I think am guessing that might be the corrections for the fuel viscosity / piston leakage thus associated piston force corrections etc the DS pumps can do vs the DB pumps that don't have the optic sensor feed back ???

Might be something to look into if a fishbiting IP can be caused by a advance piston being sticky and the stepper motor is searching trying to correct and thus timing moves sporadically and corrects some and the injection time variations causes the bite feeling ?????

 

[schiker]

Uhhhggg I think I have it backwards in above posts. I looked up reed valve and "it was so simple like the gitterbug it plum evaded me". I see that mechanism now. Also after PM'ing Bison some I think it pushes in the other direction to advance timing. The reed valve is just a check valve. Correction to follow and I am going to add pics to Bison's thread too and he may clear up some of the flow logic since he has pressure specs. Hang on I am going to post a few more pics.

 

[schiker]

Transfer pump flow path differential to housing: This part is the same and I believe correct.

Pic 1. From the distributor (head?) Charge side or transfer pump pressure.
Pic 2. "Banjo screw" allows flow to this hole from pic 1.
Pic 3. Goes thru IP aluminum body.
Pic 4. Into the Advance piston bore.
Pic 5. Hole / slot in Advance piston for flow from hole in pic 4.
Pic 6. The exit to the housing pressure cavity under the cam ring.

 

[schiker]

The advance piston mechanisms:

Pic 1. The PMD side of pump cover for the advance piston/bore.
Pic 2. Cover removed you can see the reed valve (thin metal strip). The big holes are for springs I belive. The cover is machined symetrical so you can't put it on wrong. Flats for the springs drill points for clearance of the little cap screw holding the reed valve.

Pic 3. The reed valve loosened and moved over to show port.
Pic 4, 5, 6. Show the ports lead down to the spool valve.
Pic 7. The advance piston with seal ring gone has a little rod that holds the spool slide in.
Pic 8. The spring, spool slide, and button the stepper flapper hits to push the spool slide.
Pic 9. Shows approx. where the spool body could be to direct flow to appropriate direction.
Pic 10. Just showing the spool slide and button are hollow to allow flow for lubrication and keep stepper motor end from hydro locking.


So the transfer pump pressurizes through the reed valve which checks and can bleed off pressure to the housing via the other port and the hydaulic ram cavity is in pic 2 or the PMD side to push back in to advance time. The stepper motor could maybe adjust for fuel viscosity and provide cold advance.

 

[turboaudi]

i also have a advance problem with 2 of my trucks when idling they will advance timing so far they almost stall very harsh rattle . they have done this several times .i have had a scan tool on both of them the desired timing is steady around 9 the actual will fluctuate to 16-19 degrees i have to pull a pump & check the advance piston any ideas ? thanks dave