Didnt mean to start a heated argument here. Seems there are very strong convictions on both sides of the subject. I was kinda surprised to learn it's ok to run the engine with the intake removed. I mean, given my situation, probably the best way to go, but it still seems a little unusual. I'm probably gonna go without any screen. Dont have anything on hand and dont wanna buy in light of the ridiculous prices these days. Probably wont be running the engine more than a couple minutes, total. I appreciate all the guidance and advice. If I were gonna run the engine longer and without intake, I probably would "rig something up". But, this should be pretty quick to locate my leak. Hope to be "there" this weekend. I'll post results. Thanks again, to all. Either way, I've gained more confidence in order to proceed. Should be interesting....

That guy that is panning me has issues with me on the political part of the forum.

unless there is some abnormal restriction there is no measurable vacuum in intake manifold of your Diesel. There is an air flow how much per each cylinder at idle speed I cannot tell you.


here is a diesel engine that you can buy screens to install for running your engine all of the time: https://victorreinz.us/products/maxdry-meshguard-intake-gaskets.

More intake screens.
https://www.racingbeat.com/RX7-1986-1992/Weber-Intake/16627.html

https://jiminglese.com/weber-8-stack-v8-systems

In the case of an idling Engine there is generally Atmospheric pressure which is about 14.5 psi depending on where you are in relation to sea level. So if there was zero pressure on one side of a screen the most pressure you could have on the other side id 14.5 psi.

The older Chevy Diesls from the late 1970's-to 1980's had a screen set that you could put in the manifold inlet while you worked on the Engine with the Air Filter Housing off. We had and used one where I worked for 5 years.

Read the words on the attached screen shot. The other pic is from a gasoline engine.

I have mentioned this on the political part of the forum. What good is an opinion with no facts to back it up. When I provide sites that support my opinion opponents accuse me of cutting and pasting.

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84 300D, 82 Volvo 244Gl Diesel

To find out where the leak was encountered .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

There is no reason you can't run with the intake removed. No screen or any BS needed, just clear the area of any loose objects and dirt that could be sucked into the inlet.

You seem to forget that the OM606 has a throttle plate for EGR function and the vast majority of time the intake manifold is under vacuum, especially at idle. If the om606 map sensor doesn't detect vacuum at idle the ECU will trigger a Check Engine Light.

PN 6040980317

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CENSORED due to not family friendly words

I would suppose that is removed when the intake manifold is removed and we are back to no vacuum in the intake again.

Also even with the everything assembled one would think that the at idle the butterfly valve would not be restricting because I don't know anything that has an EGR that needs to be open at idle speed. That means there should be no vacuum in the intake manifold a idle speeds.

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84 300D, 82 Volvo 244Gl Diesel

Try it in a 97 E300. I have. At operating temp idle butterfly valve is fully closed. Open it by hand and CEL is triggered. The butterfly valve has 2 functions. One is to create vacuum for the EGR at part throttle and two, enriching the mixture at idle reduces NOx. The throttle plate is about 2mm smaller than the throttle body so some air can always leak around round. The throttle plate is only fully open during cold start and above ~30% throttle. Most emissions controlled modern diesels built in last 30 years operate the same way. It's imperceptible to the driver. You can hear it slam open and slam shut if you have the hood open. The throttle valve isn't strictly necessary for engine operation but it is necessary for emissions. OBD2 is set up to monitor the air throttle valve. On the 97 it does so via the MAP sensor. 95 and 96 system was a bit more primitive. The cross over pipe also contains 2 more butterfly valves that change the effective length of the intake.

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CENSORED due to not family friendly words

There's always a vacuum in the intake manifold because the cylinders are drawing ir air .

The flappers are added to restrict the intake and increase the flow of exhaust gasses and reduce emissions .

I missed what the original leak problem was .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Even at idle there's a noticeable vacuum, I once dropped my shop rag on the fresh air inlet and it was sucked partially in .

Not much in inches of vacuum but a fair goodly bit of volume .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

WOW....this thread is gettin pretty "deep"...lol. Initially, I was just wondering about running my engine without the intake manifold, and.....here we are
I'm just asking, so don't "anyone" take offense, PLEASE. Just trying to sort it out. The question: I was always under the impression a diesel didn't make vacuum and a gasser did. Why do we need a vacuum pump if the diesel engine is producing vacuum? (hint: because it's not)
Basically and in it's simplest form, it boils down to this (I've always thought): To increase engine speed in a gasser you add "air" by opening the throttle. More air means more fuel (carb or fuel injection), engine speed goes up.
In a diesel, engine speed is increased by adding fuel. More fuel, increased engine speed. Air is not part of equation, right? You can add all the air you want in a diesel but without the added fuel (IP, injectors, etc) nothing is gonna happen.
Not saying this is gospel or I have any idea what I'm talking about. This is just the way I thought things worked (all these years).
FWIW, I was messing with my 240D and the EGR valve yesterday. I had a rag stuffed into the intake throat where the butterfly is. I forgot it was there and cranked the engine (started and ran the engine)......it didn't get sucked in, engine idled normally. Without a turbo or supercharger, when a piston goes down, it is only atmospheric pressure (~14.7 psi) that fills the cylinder.
The same thing happens when we breath. Atmospheric pressure fills our lungs. We don't create a vacuum in order to breath. Normally aspirated. E300D NA.

When there is a restriction like a butterfly valve in the intake manifold the vacuum is between the restriction and the Cylinder. Putting a screen in front of that causes more restriction compared to the butterfly there will be no vacuum at that Point.

Of course the question was with the intake manifold off.

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84 300D, 82 Volvo 244Gl Diesel

In my case I find arguing entertaining. But, at the same time I also like facts.
Supporting your argument sharpens your mind.

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84 300D, 82 Volvo 244Gl Diesel

What you have proven is there is vacuum when there is a restriction. That does not prove there is measured vacuum with no restriction.

There is an air flow caused by the piston movement but the flow is caused by atmospheric presser that is around 14.5 psi (it depends on your altitude) flowing from the atmosphere to the lower pressure crated by displacement of the Engine Pistons (keep in mind that the Intake Valve and Port can be a restriction). While we normally don't speak of it that way it is actually Atmospheric pressure that is pushing the rag into the the intake.

As an example a sailing ship is not sucked forward it is the wind/air flow pushing on the sail that causes the movement. Just as the sail catching the wind/air flow moves the ship the air flow pushes the rage into the intake manifold.

As far as I know high pressure flows into low pressure.

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84 300D, 82 Volvo 244Gl Diesel

Good points "911". I, too, like facts. Many times, the demands of daily life interfere with my ability to research facts for forum posts.
Suffice it to say, there is no "vacuum" being produced. Does anyone not know the definition of "vacuum" and how it's produced. No vacuum is being produced in a NA internal combustion engine. That's a "fact".
What's being discussed, here, is air "pressure" and "velocity", moving through an orifice or "duct", be that divergent or convergent, and the effect said orifice has on air "flow". No vacuum.

by definition, full vacuum means devoid of matter, so no car has that.
we are talking partial vacuum, which is pretty much anything that is less than atmospheric pressure (14.5psi at sea level) or LOW pressure.

all cars create partial vacuum when the pistons are moving, if they didn't no air would be drawn into the compression chamber.

lets not argue semantics.

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1977 240D auto w/OM616.916 engine
2005 Matrix 5spd
2006 Prius

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