Injection pump case pressure

whitedog

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I have been struggling with how the case pressure on our little TDI engine works and today I took the time to talk with Kyle (Da Man!) at Diesel fuel injection services and man, did I learn plenty. I’ll try to share as much as I know about this.

First off, we have our transfer pump (T-pump) that pulls fuel from the tank and provides fuel flow into the injection pump (IP) case. The fuel flows into the case and feeds cooling, lubricating fuel to the high pressure side of the pump. The fuel that doesn’t get sent to the injectors, flows out the top of the pump and out the return fitting. This return fitting is what creates the pressure in the case. Remember, a pump does not create pressure, it only creates flow. It is the restriction to flow that causes pressure.

In the VP-37 injection pump, the case pressure also serves to control the timing advance. The timing advance piston is spring loaded to the full retard position and pressure acting on the opposite end of the piston advances the timing. The N108 solenoid controls the amount of pressure pushing on the advance piston by acting as a variable orifice. The more pressure on the piston, the more injection advance you get.

Here is a drawing of where it is located. It's pointed to by the long blue arrow.



And here is the basics of what is going on with the timing:



Back to the T-pump.

On the outlet of the T-pump is the T-pump relief valve. This provides protection for the T-pump in case of blockage of the return. This relief valve has been commonly miscalled the case pressure regulator; it is NOT. It is simply a relief valve. It is very common for the guts of this valve to fall out. This has puzzled me why the pump still runs pretty good and that is what prompted the call to Da Man.

This is what things can look like:



It is located in the top of the pump right next to where the hose from the filter is. It takes a 10MM wrench to remove it.

That ring that holds the plunger in is not what sets the pressure. That fitting is hollow and it has a plug in the top end that sets the spring pressure to that specific pump when the pump is rebuilt. Due to variable leakage in the transfer pump, this can’t be set for all pumps, it must be set for each pump individually, therefore the T-pump relief should never be swapped between pumps.

I was also a bit lost on how that pump could still work with the guts all falling out. Well, as is typical with me, as I was about to ask Kyle the question, I had an epiphany and realized that even though the ring is no longer in the fitting, the plunger is still sitting in there and working just like it should.

You may be asking what all of this has to do with anything. Well not much really, LOL! The case pressure is vital to the timing, but that T-pump relief valve retainer ring falling out won’t have much effect on timing at road speed. At low idle, there is lower flow, therefore lower pressure, so there can be some flakey timing then, but once the RPMs come up, flow increases and the N108 can control the timing again.

That’s about it. I didn’t ask Da Man what the case pressure on our pumps should be, sorry. I also didn’t go into the electrical control of the timing, or how this could be modified for performance. Basically, I just wanted to clear up some misunderstandings.

I'll add some pictures after I post this.
 
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ericy

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whitedog said:
I have been struggling with how the case pressure on our little TDI engine works and today I took the time to talk with Kyle (Da Man!) at Diesel fuel injection services and man, did I learn plenty. I’ll try to share as much as I know about this.
So when this thing starts acting up, what are the symptoms?

It seems like we learn more and more about these pumps all the time :D.
 

whitedog

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When what starts acting up? The T-pump relief? The only thing there that Da Man mentioned was the possibility of flakey timing at low idle.

If you mean the N108, then you will see low power, lots of white smoke, rattle, hard starting, inability to maintain timing adjustment, probably others, but those came off the top of my head.
 

greg123

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Very interesting information.

I do have a few q's re the assumptions on the thread for example if the plunger stays in the bore, they why the loss of pressure at low rpm just because the circlip is out a bit? If the plunger isn't in the bore, then pressure rise won't push it in, the spring will be more than enough to hold it out the way while diesel flows above it and into the valve body/ports.

Has Kyle actually measured case pressure on a pump with a disintergrated relief valve & one half disintergraded to test the theory? The theory elsewhere and that I have (so far) gone on is that when the circlip goes down enough, the top of the piston goes lower than the outlet hole, as the piston moves down further it's no longer in a tight bore, diesel can flow round it and straight out the uncovered port thus leading to lack of pressure, as you say the advance piston is spring loaded retarded so low rpm function is okay but max advance/high rpm function is not.

If I get a chance to run a vehicle back to back with the case pressure valve dismantled/normal and monitor timing and N108 duty cycle I'd get a bit more info. Case pressure would be good too, only I don't know where I'd tap into that! Maybe he as already done this/benched it?

Just theory talk here - I like to be convinced by trying the theory rather than just accepting it :)

Greg.
 

whitedog

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You are right Greg and I have been thinking about about doing some testing on the Beetle. Unless the bracket is in the way, I can test case pressures with the retainer out. There is a plug on the engine side, kinda towards the rear of the pump that will show case pressure, I'm just not sure if that bracket is in the way, though I think I'll be OK.

I was thinking of doing this and reading duty cycle while cold, and revving it a bit, then duty cycle when warm and revving it a bit.

I would also do the pressure tests while cold and warm.
 

The Shootist

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There is a bolt on the engine side of the pump, just below the quantity adjuster plate. I think this is intended as a pressure tap.
 

whitedog

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I have a fitting coming for that pressure tap.

And Greg, you Jinxed me. Now my Beetle smokes out the neighborhood at >2700 RPMs regardless of if the T-pump relief is assembled or not. I did use an extra T-pump relief so I know that the assembled one is correctly set.

I'm going to look at my data, but I don't think that there is much, if any difference between assembled or unassembled.
 

whitedog

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Well, I'm not going to bother reporting what I found until I check my case pressure because I gots me some problems.
 

Growler

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oh come on, spill or start a new thread and link it :)

this is a good thread BTW. keep up the good work!
 

whitedog

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After looking at the data, it looks like when warm, it makes no difference. But then, I'm working with a pump that may have troubles, so nothing is conclusive yet.

I do have an 11MM pump sitting on the shelf. Toss that in, run a Diesel Purge and see what it does?
 

Growler

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you have the ability and tools, why not

only takes a little time to swap it over
you get more done when you aren't on the keyboard tho
;)
 

whitedog

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I'm going to wait until I get some readings on the current pump case pressure. I have fittings and test hose coming.
 

greenskeeper

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My experience with this is that if the guts fall out or the valve is set to low, you get no timing advance at load....less than 10 adv.

If the valve is set too high, you get un-controllable timing advance at load or even while cruising steady.
 
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greg123

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No Jinxing, promise! Jinx clear here!

I have a smiliar issue in atm actually but that is turbo seals failed.

I guess you'll be graphing IQ, advance & maf on a wot pull to figure out what's going on?

I knew somethign was up with this one's turbo when the sky behind me was black at idle and on a pull turbo boot was spiking off the scale but maf was half requested, which all didn't add up... Hopefully it will when the rebuilt turbo comes back tomorrow night, or I'll have to sort out the wiring to the (new) maf as well.

Greg.

whitedog said:
I have a fitting coming for that pressure tap.

And Greg, you Jinxed me. Now my Beetle smokes out the neighborhood at >2700 RPMs regardless of if the T-pump relief is assembled or not. I did use an extra T-pump relief so I know that the assembled one is correctly set.

I'm going to look at my data, but I don't think that there is much, if any difference between assembled or unassembled.
 

whitedog

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Rich, thanks for pushing me to call Da Man about this. I'm still learning things about this and it looks like I may have discovered a problem I have with the Beetle. I am also verifying the information he gave me. You know how it is... Trust, but verify. :)

If you want, I'll send you a plug so that you can test pressures on pumps. Is that what you want? :D
 

oldpoopie

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LOL. I think Rich was thinking of a plug more along the lines of, "Rich from fixumhaus is also DA MAN" or something. I'll keep an eye here. These cars continue to amaze me.
 

whitedog

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OK, depending on 10MM pump or 11MM pump, pressures will be different. Also, temperature will effect things, but not so much.

The numbers I'm giving you are ballpark numbers and not to be quoted.

For a 10MM pump, at Hi idle, we should see somewhere around 12-13 Bar (175-190 PSI) at low idle, we should see somewhere around 8 bar (115 PSI)

At low idle, the Beetle is at about 9 bar (130 PSI) so I'm happy with my pump pressure.

Thanks to Kyle "Da Man" at DFIS for the information and thanks to Rich "Da Man" at Fix-um-Haus for getting me to get that information from Kyle.
 

DPM

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so can we presume that there's enough pressure even at idle to force full advance if requested? I've always wondered whether that was possible or rather if case pressure varying w/ rpm altered the timing profile.
 

whitedog

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I do not know that answer. I think the only way to test that would be with VCDS? Isn't is possible to make the timing go to full advance with VCDS?
 

greenskeeper

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DPM said:
so can we presume that there's enough pressure even at idle to force full advance if requested? I've always wondered whether that was possible or rather if case pressure varying w/ rpm altered the timing profile.
I have fooled around with this after discovering the guts were out of the valve. I had to adjust the recess part of the top of the valve with a punch to get the timing right. Recessed to far and the pressure is too high causing too much advance (I could hit 25deg advance just accelerating slowly from a stop). Recessed not enough and the pressure is too low causing not enough timing advance.

I may have the theory wrong but that valve definately effects timing if it is not set correctly for each individual pump.
 

whitedog

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Case pressure comes right up when starting. While cranking it was maybe 30-35 PSI, then it came all the way up as the engine started. This is regardless of which valve was in the pump. I guess I could put that disassembled valve in and play with the setting to see what it does. I have a depth guage and could move it a set distance and see what happens.
 

Herm TDI

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Dawg...I have a question.

Would this valve cause the idle speed to surge?
I have a local owner who's (2001 Jetta 5Sp) idle speed is surging at normal operating temps.
 

whitedog

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Herm, if it was failed such as the spring breaking, I can see problems occuring, but otherwise, just falling out presents no problems in normal operation. (Performance application may be different, but I'm not going there.)
 

mrchill

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That also depends on other variables...it CAN do that....it usually doesnt. A bad fuel shutoff...or misplaced seal does that much more often. Also....the case pressure increases with rpm. The max safe case pressure sustained is 150-160..then the fun begins. Excessive case pressure can seize a pump head so fast your head will spin. The case pressure reliefe valve does a good job of keeping the aggressive right foot in check.
 

whitedog

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Transfer pump relief. :D

Kyle is a big stickler for accuracy, only exceeded by... me. :)

Chris, I was thinking of using a clamp on the return side just to see if I could raise the case pressure, but A) the hoses on the injector returns would pop off and 2) I don't like that head seizing thing. I think I'll drop that test.

I did check a couple more things today. Basically zero back pressure on the return side, also there was about 50 ML of fuel in five seconds at Low Idle. I don't know what this means, but I'm just throwing itout there in case anyone is curious.

I also realized I need a new 300 LB guage. Mine starts at 20 PSI. :(
 

mrchill

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There isnt much benefit in increased case pressure. Increased timing? YES! Increased injection pressure? YES! Increased fuel volume? YES! We can do the last three....and there wil be gains. I may add a pressure sensor to mine just for kicks.
 

whitedog

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Watching case pressure isn't that much fun. It jumps up at start-up, and holds steady, then increases with RPM. It's all dependant on that resistance to flow. More flow, more pressure.

But yeah. I can see no need for increased pressure, unless it allowed faster advancement of timing.

My next project will be to figure out if the N108 controls fuel into the advance piston or controls fuel coming out of the adavance piston. I thought I had it figured out the other day, then realized I had things backward in my head.

And does it really matter? And if so, what does it matter?

I actually broke down and bought a book from Bosch so I'll be able to do some additional in depth reading on it soon.
 
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