injector pop?

The VP44 has the same issue. You do not need an external air leak to create cavitation.

I have seen/tested a lot of delivery valves, I have never seen one worn to the point of not functioning properly.
 
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BC847 said:
@ chevota84, I don't understand where that air you describe is coming from. I have no leaks in the fuel system that would allow air in.
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Crazy high case pressures seem to cure this in the ve's which leads me to believe that vane pump cavitation is the main cause.
The only thing that seems to be consistent is that rotary pumps do it and inlines don't at similar injection pressure which points at the IP much more then the injectors.

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Smokem said:
The VP44 has the same issue. You do not need an external air leak to create cavitation.
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As I understand cavitation, it's induced by low pressure exerted on a liquid such that said liquid is flashed into a vaporous state (see boat propeller). Upon resumption of normal pressure said vaporous bubbles collapse back into a liquid. . . .. correct?

You would have to add heat to maintain the vapor at a constant reduced pressure, changing nothing else . . . . correct?
 
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Oh, and I don't know where the air comes from either :confused:

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I seem to recall in the Distributor Pump Bosch book a section/picture(s) concerning cavitation and it's actual effect on the case/passage damage regarding the VE. I would have to look back through it, however it seemed well documented and a known issue.
 
Theoretically it shouldn't gave the ability to cavitate if the system is closed, correct?

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Just so it's been said, my fuel system consists of:
- A modified stock/OEM fuel pick-up canister that includes enlarged fuel passages with the reservoir filled with fuel-foam, and has a lid on it to prevent the fuel from climbing the back-wall and spilling out of the reservoir during hard acceleration.
- An AN6 line comes off that pick-up assembly and goes to an adjacently mounted Walbro 392 pump.
- That pump pushed the fuel through an AN6 line to and through an oversize fuel filter at the engine.
- The fuel then goes through an Areoquip bypass type regulator.
- And again, through an AN6 line to the IP.
- The IP return and injector returns are of AN4 lines.
- They go to a common manifold in the engine bay and by way of a common AN8 line, ..
- Goes through a fan assisted fuel cooler . .
- And finally back into the fuel tank's pick-up reservoir.
 
Smokem said:
I seem to recall in the Distributor Pump Bosch book a section/picture(s) concerning cavitation and it's actual effect on the case/passage damage regarding the VE. I would have to look back through it, however it seemed well documented and a known issue.
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I've got a few of those books and confess I've not read all the way through them. :eek:
 
Now im no expert in this department, so pretty much take everything I say with a grane of salt. But with the experance I had with my truck doing it to me these past couple weeks this is what I can comment on. Now smokem you said that every truck you seen with an upgraded fuel system has solved this issue. Well it did it with the low pressure piston pump witch understandble isn't a great source of fuel, but it also does it with the 165ghplow aird dog now. But even past that when it did it at with the lp piston pump max boost was at 42psi and when firing it back up it spit and sputter for a moment or two but ran normal after. Now with the airdog at max boost 48psi. Its much more difficult to start.and this is from what I belive is that their was greater cylender pressure. So wouldn't that support bc's thoery of cylender pressure going through the nozzles. Now not trying to pick sides or say I have any clue if this even helpful information on the subject, but its what I know from first hand experance.
jon
 
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I can't really begin to explain how completely irrational the thought of cylinder pressure causing this issue is, and I work on injectors every day.
 
BC847 said:
At best our discussions have perhaps covered a few of the more commonly seen avenues that could cause the problem. Thing is, they don't hold up when the question includes why the issue doesn't occur with rolling off the throttle.
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Actually it makes perfect sense. When you roll off the throttle, the vane pump is not decreasing in speed drastically, if the assumed cause was cavitation.
 
If its pushing air into the injector body where is the fuel going? Since liquid cant be compressed how would cylinder pressure push the fuel back enough to allow the injector to open?

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Smokem said:
Actually it makes perfect sense. When you roll off the throttle, the vane pump is not decreasing in speed drastically, if the assumed cause was cavitation.
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Is the issue coupled with a great drop in RPMs? At what RPM is this happening? Then I could see that.

However the vane pump uses centrifugal force to force the vanes out and act like a governor. Unless the vane slaps the

Going full blast, the vane pump is moving enough fuel to make 500hp and the rotors spill port is covered. Let off the throttle, spill port uncovers but at that RPM, the vanes should have the centrifugal force to keep moving fuel. The pressure is maintained by a fixed sized relief hole.

I think the rotor is cavitating, not the pump. Still a huge amount of fuel trying to get somewhere but the rotor is moving back and forth in a rapid pace. Boost is keeping the fuel pin pushed down, the fuel limiting collar is still keeping the spill port mostly covered. Now boost drops rapidly and the collar moves away from the head. Rotor is still moving at a good clip. It then starts circulating the fuel in a round robin way causing a vapor lock.

I am just thinking out loud here.
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The problem I have with the cavitation concern is: How is that introducing air in the injectors?

- Spring pressure keeps the injector's needle on it's seat, correct? The hydraulic pressure of the incoming fuel lifts it.
 
Just to put some more info in this, my truck has 5x14s and a LPLP with stock inlet lines.

I had an S300 which I could boost up to 45 psi and let off at will with absolutely no ill effects. I recently added compounds and 'gated them off so total boost couldn't exceed 50psi. After this, if I let off my throttle too quickly my truck will stall.

Not to argue, just a note and some food for thought. My truck has a manual transmission. Even if I don't push in the clutch when I let off it stalls, so wouldn't that bust the sudden deceleration of the vane pump? The trans is keeping the engine spinning and the vane pump is geardriven so it shouldn't be decelerating that much. Not nearly as bad an a non-lockup auto anyways.

Just wondering.
 
BC847 said:
The problem I have with the cavitation concern is: How is that introducing air in the injectors?

- Spring pressure keeps the injector's needle on it's seat, correct? The hydraulic pressure of the incoming fuel lifts it.
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With a boat prop, it is constantly surrounded by water. However, when cavitation happens, the prop is spinning so fast, water cannot introduce itself.

Like a vacuum, put your hand over the suction side of it. The motor speeds up but nothing is being sucked in. That is kind of like the cavitation of the rotor I am talking about.

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What I am trying to say:

Diesel is foaming due to a sudden and rapid decrease in the intended direction.

Posted via Velocity LG ALLY
 
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