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TDI 101 Got a simple/basic TDI question? Are you a newbie (new to the forums). Feel free to post your question here.

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Old March 20th, 2017, 18:46   #16
KLXD
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Originally Posted by oilhammer View Post
Really? Isn't the N75 and N18 "open" from the source (vacuum pump) side to the exhaust (air cleaner) side during much of its normal operation? The EGR and VNT are not self-venting, so that vacuum needs to go somewhere, which means if it is constantly venting some vacuum, then it has to constantly be producing some vacuum, and that is going to be pushed into the crankcase. Obviously, this is a very small amount (volume) and the engine is designed to accommodate this. Essentially a tiny bit of filtered air (air cleaner post filter) being pushed into the crankcase in some manner most of the time, and being "lost" in the normal crankcase pressure scavenging that occurs as the inlet air is pulled past the PCV right where the heater sits.

At least, that is what I remember from school. If the N75 was just allowing all the vacuum it has available all the time then the actuator would just stay pulled down all the time the engine is running. Same for the EGR solenoid.
Maybe I'm mistaken but I thought the common port on the valves went to the actuators, the NC port to the pump and the NO port to the air cleaner so the pump would only suck on the actuator when the valve was energized. When it deenergized the make up air is applied to the actuator from the air cleaner.

I think it has to be thus. If it were plumbed as you say with the pump going to the common port, when the valve deenergized the actuator would be locked up. No make up air.

Are not N75 and N18 pulsed for partial actuation of the TC and EGR valve?

After further thought there would be some flow at idle but only while the EGR is being controlled. The TC is out of the picher but during the time the EGR valve is open at idle N18 would be modulating the EGR position so there would be some small flow as N18 opens and closes.

Unless the EGR is either completely open or closed. I dunno but I thought it was modulated.
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Last edited by KLXD; March 20th, 2017 at 20:33.
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Old March 20th, 2017, 20:24   #17
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Originally Posted by Dieselmonkey02 View Post
One other thing is that the pistons sweep the same volume going down as they do going up. So the will move some air around.
very little ... how i know this is my buddy Tom did a vacuum pump delete on his ALH to fit it into a bay window bus ... basically it had ZERO crankase pressure, nada .... same motor running previously with a vac pump had tons of what everyone is wrongly calling blowby... real blowby is smoky... a healthy ALH with vac pump chimneys clean air that is almost 100% vacuum pump exhaust
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Old March 21st, 2017, 05:13   #18
oilhammer
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Originally Posted by KLXD View Post
Maybe I'm mistaken but I thought the common port on the valves went to the actuators, the NC port to the pump and the NO port to the air cleaner so the pump would only suck on the actuator when the valve was energized. When it deenergized the make up air is applied to the actuator from the air cleaner.

I think it has to be thus. If it were plumbed as you say with the pump going to the common port, when the valve deenergized the actuator would be locked up. No make up air.

Are not N75 and N18 pulsed for partial actuation of the TC and EGR valve?

After further thought there would be some flow at idle but only while the EGR is being controlled. The TC is out of the picher but during the time the EGR valve is open at idle N18 would be modulating the EGR position so there would be some small flow as N18 opens and closes.

Unless the EGR is either completely open or closed. I dunno but I thought it was modulated.
Easy to test. Put a vacuum gauge on the vent line to the air cleaner. You'll see it has some vacuum all the time. Hence the constant, albeit small amount much of the time, flow of clean filtered air through the vacuum pump into the crankcase, and out the breather.
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Old March 21st, 2017, 05:51   #19
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Well can someone post a video of an engine that they think is healthy so I can get an idea of what I have. Or I guess I could post a video of my engine also
Your worrying too much about something that's normal for diesels, high compression gives lots of blow by off load and idle. It perfectly normal like guys said. My oil cap jumps all over the place when left loose.
Not using much oil? Motor on!

If your still paranoid get a manometer and test it. Don't know specs for alh though
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Old March 21st, 2017, 06:17   #20
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I will agree with most here, drive more, worry less.
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Old March 21st, 2017, 06:18   #21
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The piston sweep is usually mitigated mostly by one piston going up and one going down.
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Old March 21st, 2017, 06:20   #22
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A compression test should tell you if there is any significant problem
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Old March 21st, 2017, 20:07   #23
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The piston sweep is usually mitigated mostly by one piston going up and one going down.
this ^^^
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