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Is the 1.7L D-Jet Vac Hose Diagram @PP Correct?

I've been looking into the PCV valve operation and noted that the 1.7L vac hose diagram at the PP site:

http://www.pelicanparts.com/914/technical_specs/914_17FI_diag.htm

...shows the PCV valve connected to a port on the air filter, not the intake manifold. The 2.0L diagram shows it connected to the intake manifold.

I thought it was odd to have a PCV valve w/o vacuum, so I looked at the Factory Workshop Manual tonight. From what I can see (volume 2, pages 0.1-1/6 and 0.1-1/13), on the 1.7L, the PCV is connected to the intake manifold, not to the air cleaner.

Can someone with a 1.7L verify what is the correct connection?
Old 04-07-2003, 05:29 PM
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Hi Brad, Haven't seen ya around lately
Just went out to look at mine and took a pic. It is connected to the intake.
bruce
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Old 04-07-2003, 07:11 PM
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Mine goes to the manifold, near to where the pp diagram shows it. On the diagram, the solid rectangular unit is the intake manifold, and the "air filter is represented by the broken circle. It's easy to confuse them on that drawing the way it's labeled. I had to think a lot about mine until it was clear to me.
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Old 04-07-2003, 07:14 PM
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Quote:
Originally posted by hardflex
Mine goes to the manifold, near to where the pp diagram shows it. On the diagram, the solid rectangular unit is the intake manifold, and the "air filter is represented by the broken circle. It's easy to confuse them on that drawing the way it's labeled. I had to think a lot about mine until it was clear to me.
I agree, in looking at Bruce's photo and from what you've said, at least on the later 1.7's, it's connected to the back of the intake manifold, as one would expect. The PP diagram shows the hose going to the back, but if you look closely, it appears to be connected to a nipple on the air cleaner.

Others have told me that early 1.7's lacked a PCV and had a hose that went from a port on the filler to the air cleaner. I'll look at my parts diagrams and check this out.
Old 04-08-2003, 06:59 AM
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Brad;

I think you've got it right as regards the early vs. later 1.7s. I have a '72 and before I removed the original air filter the crankcase used to vent to an inlet on the filter box and there was no PCV. I think the later cars did connect to the manifold with a PCV as you say.
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Old 04-08-2003, 08:41 AM
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My 72 has the PCV connected to the airbox, but it also does not have the decel valve.

If the PCV routing is wrong it would not be the first deviation from stock I have found.
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Old 04-08-2003, 08:52 AM
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Quote:
Originally posted by jkeyzer
My 72 has the PCV connected to the airbox, but it also does not have the decel valve.

If the PCV routing is wrong it would not be the first deviation from stock I have found.
I've learned a lot about the crankcase ventilation system in the past day or so....

If the PCV valve is present, it should be connected to manifold vacuum. The PCV valve uses manifold vacuum to control the entire crankcase ventilation system. The overall system includes the head ports, flame arrestor, and the fresh air supply from the air cleaner.

When the system is working correctly, when the PCV valve is open, fresh air is drawn from the air cleaner through the flame arrestor, then distributed to the heads via the hoses to the ports. The air goes down the pushrod tubes, and is mixed with blow-by gasses in the crankcase. This mixture is then sucked up through the open PCV valve and into the intake manifold, where it is burned in the cylinders.

Without this system operating properly, you get condensation in the crankcase, causing oil sludging and internal rusting (a large fraction of the blow-by gasses is water vapor).

When the car is idling, you have a large vacuum on the PCV valve, which causes the disc to be pulled against the upper stop, which limits flow through the valve. This prevents a large air leak which would affect idle performance and mixture. As engine speed is increased and the throttle is opened, the valve is partially open and flow increases, permitting crankcase ventilation. As engine speed and load further increases, blow-by pressure increases and the valve remains open, even when manifold vacuum is low (i.e. heavy load).

The PCV also prevents backfires from propagating into the crankcase, as it shuts tight under positive manifold pressure. If the backfire progresses into the air cleaner and into the fresh air system for the heads, the flame arrestor stops the flame front from reaching the heads and prevents a crankcase fire or explosion.

For this system to work correctly, it must be properly hooked up, and the PCV valve must be in good working order. Mine is at least 25 years old - it appears to work OK, but I'm replacing it with a new valve. I don't know if PP has these valves, but my local Porsche dealer has them and I've got two on order - hope they actually show up.
Old 04-08-2003, 10:06 AM
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Early 1.7's do not have head ports and the flame arrestor as far as I know. Mine at least has no provisions for the head ports.
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Old 04-08-2003, 10:23 AM
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Quote:
Originally posted by jkeyzer
Early 1.7's do not have head ports and the flame arrestor as far as I know. Mine at least has no provisions for the head ports.
That is in agreement with the Factory Workshop Manual, too. Early 1.7L's had a rudimentary crankcase ventilation system that used a fixed orifice for metering instead of a PCV valve. In 1972, they went to the system I described above. As the manual says:

"Crankcase ventilation from 1972 model"

"Crankcase ventilation has been considerably improved in the engine by ducting fresh air from the air filter. This modification reduces crankcase condensation and icing at low outside temperatures."

As a result, I would suggest that owners of 1970 and 1971 1.7L cars without the PCV valve system change their oil regularly at 3000 mile intervals or more frequently, particularly in cold or humid environments, to prevent sludging and engine corrosion.
Old 04-08-2003, 10:43 AM
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BTW, Bruce, thanks for the picture!
Old 04-08-2003, 10:44 AM
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