Injector opening pressures..

[darrenjlobb]

Hi guys..

I recently had my injectors tested, and cleaned, the guy said one was slightly down on the other, but after a few cleans, is almost 99% back up to full capacity again, so that should be fine, but one thing he said, was they have a "very high opening pressure"

Im thinking this could be causing problems... i am now running with a new steel headgasket, new t25 hybrid turbo, but something seems to be really holding it back.. maybe even a timing issue..not sure where to go next.. is there any ways of checking injection timing..?

[burn_your_money]

Static injection timing can be checked using a dial indicator with the engine at TDC. You can check dynamic timing using a pulse generator off one of the steel injection lines however I don't know of any chart to compare that info to.

What exactly does "very high opening pressure" mean?

[anto]

Surely if the injectors have a higher than normal opening pressures then itl take longer for the pump to build that pressure (compared to standard injectors) resulting in slightly retarded timing?

[Rabbit on Roids]

yea, thats called artificial retard. just like worn out injectors are artificial advance.

[darrenjlobb]

Ah, so im looking at possibly advancing my timing more to get more from it...?

Its pretty knocky at idle at the moment... so i thought it was plenty far enough... is this a good indicator its already advanced enough, and are there any ways to see if the dynamic advance is working...?

[anto]

I think the only way to see if your dynamic advance is working as it should is to have a gauge measuring internal pressure (of the pump) in the car as you are driving.
There are set pressures it should reach at each rev range as far as i know.
Cant remember what these are exactly but hagar on vwparts forum has mentioned them and im sure a few people on here could elaborate on them as well.
Am i right in saying dynamc advance is directly related to internal pressure or are there other factors? Id say there is knowing the complexities of these pumps....

[Rabbit on Roids]

i remember hagar or someone saying that optimal timing is achieved with 74 psi internal pump pressure. dont remember at what RPM, but its there, i read it one time, so its still there somewhere.

[gigaz2]

dynamic timing is altered by the position of the timing piston, it can relate to pressure on THAT pump, if you change timing shims or spring the relation changes.

 just to say that 74psi might be 12º for his pump and 3º or 20º on a different pump

[Rabbit on Roids]

pick my quote apart why dont you? i understand the whole spring and spring rate and ***. ive torn quite a few of these pumps down and rebuilt them.

[smutts]

My GUESS is that about 35 to 40 psi is fairly standard transfer pressure for these pumps at 1000 engine rpm. Hagars plot and a DI ford plot crossed at this area. But who knows? Bosch won't say. How much persuasion would be needed?

[Rabbit TD]

i remember hagar or someone saying that optimal timing is achieved with 74 psi internal pump pressure. dont remember at what RPM, but its there, i read it one time, so its still there somewhere.

I'm fairly new to the workings of the injector pump.  One question though, what exactly is meant by internal pump pressure in the first place.  As I see it the vane pump sucks the fuel in to fill the pump and once it's full the rest just goes back to the tank through the return line doesn't it?  I just put a lift pump on my Rabbit a few weeks ago and at first I figured after the pump filled it would shut off with the engine not running and only the lift pump. Since it has a free path back to the tank anyway how does the IP actualy build pressure running or not with a free return flow exit.  I know I'm missing something here but what is it

[Rabbit on Roids]

the banjo bolt has only a tiny orifice. so that the pump has to build pressure inside before the fuel can go out the bolt and back to the tank. so the faster the vane pump in the IP spins, the more fuel is pumped in, and the higher the internal pressure. thats how the advance system works, off the internal pressure. higher internal pressure = more timing advance.

[gigaz2]

pick my quote apart why dont you? i understand the whole spring and spring rate and ***. ive torn quite a few of these pumps down and rebuilt them.

only trying to clarify that there is no magical number, the only way to be sure would be to measure the advance and map it vs rpm.

[Rabbit TD]

the banjo bolt has only a tiny orifice. so that the pump has to build pressure inside before the fuel can go out the bolt and back to the tank. so the faster the vane pump in the IP spins, the more fuel is pumped in, and the higher the internal pressure. thats how the advance system works, off the internal pressure. higher internal pressure = more timing advance.

I forgot all about that little orifice in the banjo fitting.  Does a lift pump rated 4-7 psi have much or any affect on the internal pressure as far as starting the engine.  I noticed 2 mornings this week after putting this lift pump on that my new TD would not start with just 40 degree temps in the morning even with 2 or 3 glow plug cycles and I am getting power to them but I haven't checked the plugs individualy yet to see if they glow.  This engine always fired right off on all 4 before when it was a lot colder than this with just 1 cycle and the advance lever pulled.  I actualy had to use starting fluid those 2 mornings but like I said the lift pump is on all the time with the key on.  The car definately idles faster though and seems to have more power also but the air temp. is getting cooler around here too which may count for the seemingly more bost.  I'm just wondering if these pumps cause any negative issues possibly in the timing.  This engine runs great otherwise and seems to be getting better all the time, about 8,000 on it now.

[Rabbit on Roids]

my car started BETTER with the lift pump. i noticed more power at the far end of my pedal, but thats it, it doesnt idle higher or anything. i dont see how a lift pump would make it idle faster... cause there is more than 4-7 psi inside the pump even at idle.