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post #1 of (permalink) Old 07-05-2009, 04:33 PM Thread Starter
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Vacuum lines MC2150 non smog setup

I found a few diagrams that explain how to setup the vacuum lines on a "smog" engine. MC2100-5 - eSnips, share anything How do I set up my vacuum lines for non-smog with my Motorcraft 2150 with 1.21 venturi? The diagram in the link above doesnt really explain this. The engine is a AMC 304 with stock cast iron intake manifold. The only line I am positive about is the line from the distributor. It shall be connected to the pipe below the choke housing and arm.

I suspect that not all the non used vacuum ports can be plugged off. I guess that the vacuum pipe on the power enrichment valve housing should not be plugged as this may affect the power valve. Also the 1/2" sized pipe on upper part of the body should most likely not be plugged.

Does anyone have a diagram or a photo? Do I need the PCV? What is PCV? Do I need EGR? What is EGR? Direction of PCV valve? Connection point on both manifold and carb.?

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post #2 of (permalink) Old 07-05-2009, 05:52 PM
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PCV is the Positive Crankcase Ventilation system, and is something you want. It removes the combustion gasses and byproducts from the engine interior, and is completely benign to engine performance. It is simply connected to manifold vacuum, wherever you can find it.

EGR is the Exhaust Gas Recirculation system. It introduces some exhaust gas into the intake stream, which causes the combustion to take place at a lower temperature, which reduces the formation of oxides of nitrogen. Although illegal to do so, a lot of guys remove it because it interferes with throttle response and driveability. The EGR system details vary, but basically there is a passage from the exhaust manifold to the intake manifold, and a vacuum-operated valve controlling the flow. You need to securely block off both the intake and exhaust sides of that passage, and remove the valve.

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post #3 of (permalink) Old 07-05-2009, 06:20 PM Thread Starter
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PCV on a AMC 304

Thanks.

Is the hoses related to PCV connected to my MC2150 carb. or from oil-cap to air filter case?

Also, on the stock AMC intake manifold there are two holes inside the intake bore of the manifold that are connected with the crank case / engine (goes to the undersinde of manifold). Is this also a part of the PCV?

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post #4 of (permalink) Old 07-06-2009, 05:58 AM
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The PCV system has a hose going from manifold vacuum at or near the base of the carb, to the PCV valve, usually stuck in a valve cover. Then there's a hose going from a grommet at the other end of the valve cover or the other cover in a V engine, to the air cleaner. That provides a round trip flow of air from the air cleaner through the engine, the PCV valve and into the intake stream.

I'm not very familiar with the AMC V8s so I don't know what the holes in the manifold might be for. If they're plugged from the factory they may be casting core holes. How big are they, and are they threaded?

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post #5 of (permalink) Old 07-06-2009, 07:08 AM
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AMC V8 PCV is located at the rear of the intake manifold, just in front of the EGR. As Jim said, they get manifold vac, usually from the carb base.

My EGR has been DOA for years with no real apparent issues.

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post #6 of (permalink) Old 07-06-2009, 02:58 PM Thread Starter
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Holes inside intake manifold - AMC 304

Jim, the holes I mentioned can be seen when I lift off the carb and look straight down in the manifold. See attached photo. On a dismounted manifold I have noticed that the holes end up under a rivet mounted 1mm thick steel pan. The holes are about 1/2" to 3/4" in diameter. I thought this must be a part of he PCV system. At first I found it quite strange that engine should suck non-petrol-mixed-air from below the manifold. Can anyone explain this?
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File Type: jpg AMC_4bbl_manifold.JPG (76.5 KB, 2 views)
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post #7 of (permalink) Old 07-06-2009, 03:50 PM
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I think I see a plugged hole in the bottom of the right primary. Is that what you're talking about? Are the holes horizontal into the neighboring chamber, or do they go through the bottom into the valley? They're certainly not related to the PCV system. Might be part of the EGR, but if they're plugged I wouldn't worry about them. Maybe a bigger picture, with circles and arrows and a paragraph on the back of each one telling . . .

What the PCV system does is remove the exhaust gas that squeezes past the piston rings. That gas is called blow-by. It contains combustion by-products including water vapor. When vapor condenses it combines with other combustion gasses and forms acids and oil sludge. The PCV system sucks blow-by from the engine interior and puts it into the intake stream where it is burned, and most is blown out the exhaus. A little gets past the rings and goes around again.

The other hose carries air from the air cleaner into the engiine to provide a constant purge flow.

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Last edited by Jim_Lou; 07-06-2009 at 03:54 PM.
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post #8 of (permalink) Old 07-06-2009, 04:03 PM Thread Starter
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PVC system of AMC304

OK. Thanks. I appreciate this feedback. See the attached photo. The holes go straight through the bottom of the casting. No threads. They end up under the mentioned pan which is vented inside the engine. I discovered this when I cleaned the intake manifold with water. The water flowed straight throug and down on the ground. (Dismounted manifold). I find it strange that I need the PCV hose when the engine already suck blowby gas through these holes. Just wondering and trying to understand the design better.
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File Type: jpg AMC_intake.JPG (37.9 KB, 2 views)
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post #9 of (permalink) Old 07-06-2009, 06:09 PM
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The engine isn't going to run right with those holes open. Guaranteed. I have no idea why they're there, but you'll have to plug them. They might be of a size that you can tap them 3/8" tapered pipe thread and put plugs in them.

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post #10 of (permalink) Old 07-06-2009, 08:04 PM
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They are called "Floor Jets." The holes don't go into the crankcase, they go into the exhaust crossover - unless the manifold has rusted through. They recycle a tad of exhaust gasses back into the intake. It's called Exhaust Gas recirculation. It's the early form. It controls Nox and HC emissions.

They are a fixed constant opening. They were used for a few years, then dropped in favor of something more controllable - an external valve - called the EGR valve.

Most of the time the small orifice is worn bigger, giving too much exhaust, affecting performance too much.
Tap and plug them.
Don't use epoxy as plugs - the plugs can come loose and get under a valve, causing lots of problems.

The PCV is an entirely different system. It has a hose from the intake manifold to the crankcase or valve cover. In that hose is the PCV Valve. It sucks the fumes out of the crankcase - keeps the engine oil clean.
Then at the other end of the engine or rocker cover, it has a fresh air intake. It should allow fresh clean air into the engine. Usually it gets it's air from the air cleaner.
The idea is to have clean fresh air come in one end, sweep through the engine to gather up the fumes, then get pulled into the intake to be burned. It's not detrimental to the engine at all - in fact, it helps it stay clean and live longer.

Last edited by RRich; 07-06-2009 at 08:56 PM.
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