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Old 25-07-2016, 15:39   #31
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Re: answer me this, if you will....

must be a one way valve in their somewhere
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Old 25-07-2016, 15:44   #32
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Re: answer me this, if you will....

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Originally Posted by knockabout View Post
must be a one way valve in their somewhere
Sure, the intake valve. It's not closed when the piston is going down.
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Old 25-07-2016, 16:04   #33
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Re: answer me this, if you will....

All this pondering about manifold vacuum / sucking fuel in diesel engines is pretty bizarre. If all your fuel tanks are in the bilge and dependant on a functioning transfer pump to get hr' up consider a day tank with auccillary deck fill. Over flow it to tank of choice (same one you are using) Return from injectors goes into day tank so it is always full.This makes bleeding so easy This works doubly well up here where we use diesel stoves
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Old 25-07-2016, 16:23   #34
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Re: answer me this, if you will....

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Originally Posted by Guy View Post
Sure, the intake valve. It's not closed when the piston is going down.

I've been watching this thread and laughing in sporadic fits.....


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Old 25-07-2016, 20:41   #35
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Re: answer me this, if you will....

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Originally Posted by a64pilot View Post
No, a simple mechanical injector cracking pressure is I believe around 120 bar or about 2000 PSI. It may be lower than that on the older designs, I don't know. Injectors are one of those things I have serviced, I just R&R them.
Common rail systems fuel pressure will run in the tens of thousands, my Duramax runs I believe about 30,000 PSI stock, it is largely the magic that makes common rail as good as it is, you can get lots more fuel in the engine in less time allowing higher RPM etc.
Of course a Diesel has no vacuum, it has no throttle valve, actually it has some vacuum, it's measurable as air has mass, but it's trivial and for all intents no vacuum is correct.
A spark ignition engine is throttled by varying air and fuel together keeping hopefully a stochimetric (sp?) ratio, Diesels only vary fuel, they pull in a full amount of air regardless of load, operating very lean like that is one reason for their efficiency


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A64, I'm almost always with you but in this case no.. Diesel injectors inject directly into the cylinder while the cylinder is under compression. (In some cases into a pre-chamber but the pre-camber is under the same compression as the main cylinder.) Hence the need for timing of the injector pump to squirt at the correct time because the fuel burns as soon as it is injected.
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Old 25-07-2016, 21:05   #36
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Re: answer me this, if you will....

Greetings Zee As long as there are no air leaks, the fuel will stay in the line and high pressure pump, thus would start easily. When running, the pressure pump is drawing fuel from the tank. You might check to see if the tank is vented freely, because if it starts drawing a vacuum, it causes surging before stopping completely. I had a problem once with crud blocking the vent line, and it began surging like that.
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Old 26-07-2016, 16:56   #37
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Re: answer me this, if you will....

[QUOTE=a64pilot;2174681]No, a simple mechanical injector cracking pressure is I believe around 120 bar or about 2000 PSI, operating very lean like that is one reason for their efficiency

You are right I added a 0. I have the test report for mine in front of me, Tested as received, 1600-1650, spec, 1975 psi.
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