Author Topic: Injection Pump After New Nozzles (Read 3241 times)

Op-Ivy · « **on:** February 01, 2009, 01:28:31 pm »

I just put new nozzles into my injectors. Initially I had been a bit worried as the injectors had never come out in over 470,000km! :shock: Everything went well though! Good power now and everything seems to be working well.

However, I have noticed that my idle is slightly lower and the engine sounds a little advanced. I can faintly hear the marbles. The old injectors were breaking at about 130-135bar and I calibrated the new ones to 150-155.

My question is: What changes would I see to my dynamic timing and internal pump pressure with an increase in breaking pressure?

I thought about it and tried to figure it out but I keep going around in circles. I did a search because I remember there being a thread about this but I didn't have any luck.

Thanks, Matt

dillenger1 · « **Reply #1 on:** February 01, 2009, 02:03:55 pm »

I think you have to tap the regulator to change internal pressure.The high pressure side is seperate.Its just taking longer for the pumo to build the prerssure.I would think that would retard your timing.

vanbcguy · « **Reply #2 on:** February 02, 2009, 12:47:21 pm »

Injectors with a higher breaking pressure will cause the high pressure side of the pump to take longer to create sufficient pressure for them to pop. This means the timing will be retarded for a higher pop pressure injector versus a lower pop pressure injector with no other changes to the pump.

This impacts your static timing as opposed to your dynamic timing - it is the equivalent of moving the pump as opposed to changing the internal pump pressure.

dieselherb1 · « **Reply #3 on:** February 03, 2009, 07:07:38 am »

So does he need to readjust his timing?

Op-Ivy · « **Reply #4 on:** February 03, 2009, 07:22:59 am »

I shouldn't. I can probably compensate by increasing the internal pressure. Thanks guys.

vanbcguy · « **Reply #5 on:** February 03, 2009, 09:29:39 am »

I'm pretty sure that YES, you do need to change your static timing.

There's two factors here, static timing and dynamic timing...

Static timing is where the pump is timed to with zero internal pressure, it's what you are changing when you loosen the pump bolts and adjust the pump. Static timing is not changed whatsoever by pump internal pressure but it IS changed by injector breaking pressure.

Dynamic timing is the advance that is added "on top" of the static timing when pressure builds up inside the pump body, due to the vane pump spinning faster. Diesel still burns at the same speed regardless how fast the engine is spinning. In order to make sure that the "burn" happens at the same place in the engine's cycle (ie peak pressure pushes the piston down just after TDC) you need to inject the fuel earlier and earlier as the engine goes faster. This is what you change when you modify the pump internal pressure. Dynamic timing is NOT affected by changes in the injector breaking pressure as this only affects the high pressure part of the pump.

If you add more dynamic timing (by increasing the pump internal pressure) you may well get your timing "right" at a certain RPM range, but it won't be right the rest of the time. There's a maximum amount of advance that can be added by the dynamic advance mechanism, it can't go upwards to infinity. So if you start with retarded static timing and try and compensate by adding more dynamic timing you'll max out the dynamic timing lower in the RPM range. You'll be too far retarded at lower RPMs and you'll hit max dynamic advance somewhere in the middle of your RPM range and again become too retarded.

Vincent Waldon · « **Reply #6 on:** February 03, 2009, 11:05:27 am »

We should probably be clear here.... or at least I'm wondering if we're all talking about apples and apples.

Here's how I see it:

"Internal pressure" refers to the upwards of 100+ psi pressure on the lo-pressure side of the IP. It's provided by the vane pump and can be adjusted via the pressure regulator at the top of the IP. Adjusting the internal pressure adjusts the dynamic timing advance curve.

"Breaking pressure" is the 2300+ psi pressure available on the hi-pressure side of the IP. It's provided by the cast-iron fuel distribution plunger and is pretty much non-adjustable (as far as I know).

What *is* adjustable is the breaking pressure of the injectors... the pressure at which they "pop" open. It takes some time for the hi-pressure side to generate enough pressure to overcome the spring in the injector... and if you increase the breaking pressure it will take a bit longer, therefore effectively retarding the static timing.

Someday I'll actually do some measuring and figure out how many psi breaking pressure = a degree of timing change, but it's not uncommon for people to refresh their injectors and find their engine is actually not running as well. My guess in this case is that the worn injectors were providing a bit of "artificial" advance that disappears with the installation of properly calibrated injectors. If the pump was already timed to the somewhat-conservative factory settings this extra artificial advance will be missed immediately. :wink:

vanbcguy · « **Reply #7 on:** February 03, 2009, 07:24:51 pm »

^^^^^^^^
That's what I'm talking about!

Vincent Waldon · « **Reply #8 on:** February 03, 2009, 07:32:16 pm »

Quote from: "vanbcguy"

^^^^^^^^
That's what I'm talking about!

Yup... great minds think alike.. and fools seldom differ... we musta hit POST at the same time. ;-)

gldgti · « **Reply #9 on:** February 04, 2009, 12:00:50 am »

so, given the forums syopsis, the OP is either wrong about his hunch for the timing now being too advanced, or there is some other problem....