hybrid isuzu/cummins pump finished!

[truckinwagen]

well, I drove it out on the highway to borrow a garage today, and it drives real nice except that it falls on its face at 4000RPM.

it pulls real hard right to 4000, but stumbles and has a hard time accelerating beyond that.

I am thinking that it is running out of timing on top, I might advance the static timing a bit to see if that helps, and if it does, I might modify the timing piston cover to allow farther travel of the advance piston/ install a softer spring

-Owen

[truckinwagen]

what about increaing internal pressure a bit? I really dont want to have to remove the pump again(the only way to pull the timing piston cover is to pull the pump)
increasing internal pressure would advance further at high RPM right? as long as the piston is not bottoming out on the cover, yes?

-Owen

[fatmobile]

Right, someone graphed the curve (actually a straight line) pressure doesn't change the curve, other than to move the whole line forward.
 It makes the starting point change come in later, along with the whole line.

 I wonder if removing the shims might have advanced your high RPM timing too far.
 You did the gov mod right?

[truckinwagen]

yep, gov mod is done(pic of it early in this thread)

I suppose I could advance static timing and see if that helps, and then retard static timing to see if that helps.

should identify if it is too advanced, or not advanced enough at high RPM.

hard to believe that it could be too advanced to continue accelerating though...

it does clatter pretty loud on the throttle, but the cummins pump did that on the VW too, something to do with the injection event being really short compared to the smaller pump head.

-Owen

[rabbitman]

I think fat's correct, IIRC different IP's have different pressure regulator springs with different advance curves.

Look in the vwdieselparts forum in general, there's a sticky called "internal injector pump pressure" or something with some pretty good info in it.

[truckinwagen]

yeah, I know the internal pressure and advance spring are matched, but I was just wondering if it were possible to advance so far that it would not burn the fuel properly.

supposedly giles pumps have ridiculous amounts of dynamic advance.

regardless I could see if it was too advanced or too retarded by playing with static timing(as it affects dynamic timing)

then I could play with the dynamic advance mechanism to match what is needed(if its advancing too far I could put the shims back in, and if it is not advancing enough I could modify the advance cover to allow more travel)

-Owen

[rabbitman]

Let me rephrase that to mean what I'm thinking , there's a spring in the pressure regulator and another (much larger) spring under the advance piston cover.

I'm talking about spring #3 in this picture:


I'm pretty sure you can use a different one and get a totally different curve.

I just thought of that if your internal pressure is just not high enough, the 12mm pump with its heavier return springs might be fighting the advance piston as it tries to climb the camplate, thus never reaching full advance. So if you bump the pressure up the piston might have enough hydraulic force behind it to overcome the heavy springs and boom, more power!

[truckinwagen]

I like that!

especially at higher RPM's the heavier springs(and heavier plunger) would hold lots of pressure against the rollers.

the only seal I did not replace was the main shaft seal(I only had a 17mm shaft seal in my kit, and the isuzu pump has a 20mm shaft) hopefully the higher internal pressure will not make it leak!

thanks for that,

-Owen

[truckinwagen]

well, I tapped the pressure regulator down some(not much, like 1/100 of an inch) and saw little improvement.
after class I will try advancing static timing to see what that does

[truckinwagen]

well, I advanced the static timing just shy of where its a pain to start.
this did move the stumble up 500RPM(from 3750 to 4250) so it definitely needs more advance up top.
I will achieve this by getting ahold of a softer advance piston spring and machining the piston cover to allow more travel.

anyone know which is the softest stock VW timing advance spring?
I think it is the green one, but I could be wrong.

-Owen

[truckinwagen]

also, will running timing really advanced(at low RPM at least) hurt anything?

not sure if I should put the timing back where it was and deal with the hesitation before 4K until I can get the new advance spring, or if I should leave it where it is now until then...

ah, and other than the problem at 4K this thing is like a different car!

never thought an N/A could be transformed so much without adding a charger!
it now has power to accelerate at 60MPH, where it used to be flat out, and take forever to get to 65.

loving the car more than ever now, all I need to do is get it quiet again(between the injection clatter and exhaust, you need earplugs to drive it any distance)

-Owen

[rabbitman]

I seem to recall green being the softest.

I don't think excessive advance will hurt at high rpm but I have heard stories of pounded rod bearings, broken pistons and of course blown head gaskets. I'd really try to keep it in the safe zone, I would think that you shouldn't have to worry much at high revs though.

For punching in the pressure regulator it would make it lots safer to use a pressure gauge while doing it. I did mine a couple years ago and it was very easy to over do it even with a gauge, I'd tap it over and over and nothing would happen so I'd hit a little harder and all a the sudden the gauge would shoot up and it would start clacking harder. So instead of going from 35psi up to 45 it would jump to 55 or something. The fix is to remove the regulator, pound it all the way through and then start over.

[truckinwagen]

ok, I will pull the timing back to normal in the morning then.

now that I have more power, I find myself needing to go past 4000 less, so its not such a big deal.

not to say that I don't want to fix the problem, I will need to go as far as I can RPM wise when I take this thing to the drag strip.

-Owen

[NintendoKD]

I think we need jedi master giles here, this is pretty cool stuff, May look into something like this for my build.

cool

[truckinwagen]

will try that, but advancing timing certainly helped high RPM running(lifted the "ceiling" by 500RPM)
so I am pretty sure it needs more timing up top.

-Owen