pump pressure

[dieselpower]

hey,
besides timing advance, what does the internal pump pressure do? and how can someone change it? i have the fuel return on my pump blocked off and i think it increases the internal pressure. maybe not, but i read somewhere that increasing the internal pressure adds more power...he said it wasnt dramatic but still a power increase. there pressure also affects the govenor in some way as the higher the pressure, the lower the rpm that the throttle starts to stick at. so i want to kno what a change in pressure does.
any help would be appreciated


Mark

[dieselpower]

ok,
i just got some yogurt..UUMMM..and an idea came to me :idea: .
i think i figured out why incresing the pressure makes the throttle stick..what i thought is during the ?intake? phase of the pump where it draws fuel in the pressure is actually enough to open up the d-vales and fill the lines with fuel, and therefor make it so when the plunger compresses it's actually pushing out the fuel in plunger itself and in the lines making way more fuel go into the engine. so making the opening pressure of the d-vavle greater would get rid of the sticky throttle problem maybe?
again any info would be appreciated...and any corrections to what i have said if i was wronge with anything
thanks



Mark

[dieselpower]

i should work on thinking things out fully before i post,
but i just figured something out.  blocking off the fuel return does not increase pump pressure..well not by much anyway, because when the fuel cant go out through that little tiny hole(insignificant if you ask me)the pump pressure increases and it opens up the pressure regulating valve which recycles the fuel back into the front of the vane pump. i think the fuel return from the pump is only there to let air out if any gets trapped inside. anyway..the pressure regulating valve is adjustable, all you have to do is take out the valve, it is beside the fuel inle and it has 2 flat sides on it.  the little plunger type thingy in the middle of it actually moves up and down and the farther down it is, the more the spring is preloaded therefore making the internal pressure greater. back it out some and you decrease the pump pressure.
make sure you take the valve out of the pump and place it on a hard surface before u hammer down on the middle or else it will slip out and fall into the pump.
just make sure you dont put the spring into coilbind.
if you go too far just keep punching till it all comes out the end..a 14mm deep socket works good to suport it off the table.
this could be good for us with sticky throttle to lower internal pressure as well.
i tried to lower mine once by making the fule return orfice bigger, but at higher rpm's the fuel line would cavitate and it wouldnt get enought fuel becasue it was pushing it all away. at least this way it just pushes it back to the vane pump.

one thing to watch out for is changing pump pressure affects the timing advance curve, so you have to shim(or unshim)the timing advance spring.
hope this helps


Mark

[QuickTD]

Housing pressure should have negligable effect on injected quantity. Fuel is not compressable (at any reasonable pressure, anyway) so you cannot increase the volume injected by increasing the pressure in the lines at the beginning of plunger lift. The effect of housing pressure on timing has been well explained though. I would suspect that the increased housing pressure advances the timing and the rpm picks up a bit from the timing change alone.

 I wouldn't plug the return orifice completely. Its purpose is to flow enough fuel for pump lubrication and temperature control as well as to purge air from the system.

[fspGTD]

I guess we should start with the big question: what do you hope to gain by doing this modification?  As QuickTD has said, plugging the return fuel line orifice could potentially cause the fuel injection pump to overheat, so this modification/experimentation suggestion is not without risk.  I could see an overheated pump potentially seizing, and also the extra heat of the fuel that does get injected being heated more would also cause more of an inconsistency in the mass of fuel injected, and therefore more inconsistent performance.  I would suggest plumbing a temperature and fuel pressure gauge to assess what's going on when you do this - IE: so you can quantify how much the internal pressure increased as a result of plugging the orifice, or verify that the temperature is still in a safe operating area.  Also, it is easy to adjust the governor to adjust quantity of fuel injected.  I also haven't seen any conclusive evidence yet that the stock timing advance rate needs any change from stock design to be optimal for best fuel efficiency and power.  So, are you hoping to advance the timing by doing this, increase the fuel rate, or are you just a curious type that need to experiment to see what happens, or

Also, that is interesting that you noticed a power gain by blocking this off, but have you done any testing to make sure it's real, IE: dyno, G-tech, 0-60 time comparison, something... to quantify the results?  Stories about of people who do some magic modification and then by the seat of their pants only, deem it as a power adder, but when actually quantifiably tested on the dyno or other test, the truth comes out and the modification actually didn't help or even hurt power.  Case in point: big cone air filter in the engine compartment... people think somehow it's faster, maybe because they are confusing louder or "different" with more powerful, when in fact on the dyno it shows it actually costs the horsepower.

[dieselpower]

hey,
actually i just wanted to kno what the pump pressure does to affect the govenors ability to reduce engine speed. the rest of what i said was just me "thinking" out loud. which i should work on not doin soo much. i read it on TDIclub.com?? and i think the power gain was probably just the increase in timing below 2500 rpm(before electronics kick in). having the return blocked off does add more power verses a slightly bigger return orfice(i didnt test stock size and maybe it had to do with my launching technique)but it did add more smoke...anyway all i want to know is why does high pump pressure make the rpm's not lower down.
thanks for the input.


Mark

-edit-
what do you mean by

I also haven't seen any conclusive evidence yet that the stock timing advance rate needs any change from stock design to be optimal for best fuel efficiency and power

i have actually replaced the shim in my timing advance spring with a smaller one and machined out my timing advance cover. and again, i haven't tested it before or after my mods so i dont kno if it actually makes more power or not. are you sayin that im better off going back to stock preload on my timing advance?

-edit 2-
also my modification was not just pluging up the fuel return. it was adjusting the pressure regulating valve, beside the fuel inlet, to make a higher pressure, which i havent done yet. pluging up the fuel return was just something i did for an experiment(which i put back to normal now).

[fspGTD]

I don't know specifically in your case why RPMs aren't dropping down as fast, but as a general response I could think of 2 possible explanations: 1. more fuel is being metered, and/or 2. the timing is adjusted closer to optimal setting for light throttle.

You mentioned TDI ECU-controlled timing electronics kicking in above 2500RPM... Are we talking about an IDI motor here?  1.6, 1.9TD?  Also what kind of car and year?  (Might want to put your engine and body style / year in your sig to avoid this kind of confusion...)

Modifications to the fuel return orifice and fuel pressure regulator are interesting things to try, which I have not done, but my advice for testing these kind of "new" things are to only change one variable at a time, and measure quantitatively.

I have measured several static timing settings of the '84 1.6lTD pump (albeit outfitted with 2-stage 1.9lTD injectors.)  The stock timing advance rate (IE: the rate of degrees advance per RPM) and the stock static timing setting of 1.00mm resulted in max HP of any setting tested throughout the RPM curve until it gets above about 5000 RPM.  So, just like I said, I haven't seen any evidence that the stock timing advance rate *should* be changed...  that is why I will not be spending time looking for HP making adjustments to my fuel return orifice or my fuel pressure regulator.

Of course, different motors and injection pumps could be configured by the factory differently, those results are just based on the limited testing I've done, may not extrapolate to all IDI VW Diesel motors... etc.  So that's why I say I have not heard any evidence that stock timing rate isn't ideal...  Some advice for your testing... do let us know what you find so we can benefit from your testing!  Do be scientific in your testing and try and take quantitative measurements when helpful so the rest of us can see the results clearly.  And another note... when testing, do resist the urge to change many things at once.  You've blocked orifices, adjusted regulators, shimmed springs, relieved advance piston covers (that last one is something I think CAN help... but that's another thread.)  At what point did your RPMs start dropping more slowly and what was it compared to - all these things at once done vs stock or one combination of these modifications with another?  If you've changed all these at once, you won't know which of the various things you changed helped, vs which ones did not make any difference, or which ones even hurt.

Good luck!

[dieselpower]

thanks for the help,
well i read about that mod on a TDI forum so thats why i was talking about electronics. ya, pretty much all my mods have been done at the same time so it's hard to see what does what. what do you mean by timing is adjusted closer to optimal setting? my staic timing is set to 1.10 and my timing advance is about 1mm unshimmed(for when i had the bigger return orfice). maybe when i opened the orfice up, the rpms started to drop normally not because of the pressure reduction, but because it was getting choked off from fuel at higher rpm's. also didn't someone say that timing advance makes power all the way up to 1.17? i think i'm going to lower the timing on my car to lower noise. it's so far advance right now that in the cold it barely cranks over with the cold start pulled out(because it's igniting too early putting back pressure on the piston i think). once the rpm's get above about 3200 rpm, unloaded it just takes off and goes to about 4300 rpm..iirc. it only started after i shimmed the govenor springs.

also i have no "real" way to test out my modifications. i have a g-tech but its not one of the new compition models and i dont have a tach right now so its hard to tell what the difference the mods do.

thanks alot for the help


Mark