PCV Valve and Flame Trap Questions

calebessent · Post by **calebessent** » Thu Oct 25, 2007 10:33 am

I have a 1971 variant, d-jet, 1700, auto. My engine code is W0116192. Currently I'm working on routing all the hoses to the right places. This isn't easy, because it seems that my PO replaced hoses by guessing where they should go.

(Question 1)
I cannot find a PCV valve. It is not in the crank case breather box. I have read that some early 411's did not have them. I know it's best to replace the often-broken valve with a fixed orifice. Is mine located somewhere else, or never there to begin with?

(Question 2)
I do not seem to have a flame arrester or flame trap. I also cannot find hoses that run to my cylinder heads. Where do they visibly enter the engine bay?

Did these early 411's not have a crankcase ventilation system as robust as the newer ones?

So, I'm drawing this conclusion: my car doesn't have hoses that run from the air cleaner to the flame trap to the cylinder heads, down the pushrod tubes, and into the crankcase so that it is expelled back to the plennum through the PCV and burned in the cylinders. Is that right?

One observation I have is that light smoke jets out of the crankcase breather box hose when I try to start the car with the hose not hooked up to the filter box.

I don't have a nipple on the front driver side of the plenum (by cylinder 3) for a hose to be connected to the crank case breather box. I have one that is connected to the MPS. Is that correct?

If this is the case, I am wondering if the crank case ventilation hose is supposed to go to the dirty side of the air filter box. Here is a picture of my air filter box. It's also different than most I've seen. When I got the car, the hose from the crankcase breather box was routed to the frontmost nipple in the picture here.

Am I on the right track? Any comments or suggestions about this early ventilation system?

-Cale

wildthings · Post by **wildthings** » Thu Oct 25, 2007 2:32 pm

Only T4's and Porsches had PCV valves, if you engine were taken out of a bus you would have a different system depending on whether the bus had fuel injection or carbs. European vehicles also had some different set ups. A picture of your breather box would help.

It is good you are trying to get your crankcase ventilation hooked up correctly, way to many fail to understand the importance of this system. It affects both the operation and longevity of your motor.

raygreenwood · Post by **raygreenwood** » Thu Oct 25, 2007 3:17 pm

You have a PCV valve....you just don't recognize it. The "nipple" that comes off the breather box.....the one with the nylon circular nut...the one that connects to the red 12mm hose that goes to the plenum....that IS the PCV valve. If you remove the breather box youwill see a "D" shaped indention. That is a plastic plug. Pop it out and you will see the bottom of the PCV valve. You unscrew the round nylon nut and the PCV comes out through the D-shaped plug in the bottom.
In my opinion...the PCV valve was defective from the factory. Since it pops in and out via a combination of crankcase pressure and vacuum...it is an unplanned vacuum leak and definately screws with the MPS. It is one of the major factors for "submarining" idle and poor idle characteristics in general. Its better to make it a constant fixed orifice than a variable over which the EFI system has no control.

Put into the line a metal plug that has a 3mm orifice drilled in it....and pop out the guts from the PCV. Re-adjust idle and fuel mixture and it will run much better.

The hose routing is like this:

From the air cleaner...the filtered side only....the hose goes to the flame trap. From there it splits to each head. If your heads do not have the connections...they definately have the cast in bosses for the tubes. Drill them out and install 12mm tubes for the hoses. The flame trap is nice but not greatly important. You can plumb in a "Y" to make it work. From the heads...the air gets sucked through the pushrod tubes and exits the crankcase through the breaher box and is pulled into the plenum.

The PCV path and system of the type 4 is absolutely superb when hooked up prperly. The heads run cooler and cleaner. Ray

calebessent · Post by **calebessent** » Thu Oct 25, 2007 4:42 pm

No, there's no nylon nut that the nipple protrudes from. It's molded in. Opening up the d-shaped plug only reveals a hollow cylinder within the hollow can.

I will definately be plumbing in the hardware for ventilating my crankcase. I'll make sure I take pictures and document what's going on.

Speaking of pictures, I found one of my engine bay with the crankcase breather included. The breather exits right (passenger side). It was sitting loosely on the block and facing the wrong direction when this picture was taken.

No PCV here.

Also, in this page of this manual, you can see a breather box like mine labeled number 18. Whether or not it has a PCV is debatable. Mine does not.

-Cale

wildthings · Post by **wildthings** » Thu Oct 25, 2007 6:27 pm

The breather used on US spec carbureted engines had a 13mm (1/2") nipple that stuck out at about a 45° angle to the vertical to the passenger side. These had no restrictions, there were european variations of this I have only seen in pictures as well. If that single hose is all you use I don't know if it is best to run it to the dirty or clean side of the air cleaner, I think VW did it both ways. If you added a orificed line from the crankcase to the plenum as Ray is suggesting you would want your breather to go to the clean side of the air filter as it will draw air into the crankcase at times.

raygreenwood · Post by **raygreenwood** » Fri Oct 26, 2007 6:58 pm

Yes...the parts sub-assembly listed as 21...is the US spec fuel injection part. It came on al 71 and later 411 and 412 with D-jet. I have rarely seen the other ones listed as 18, 19, 20. Probably carbed as wildthings noted.
But...if you use a fixed orifice inserted into the line...those will work just as well as the stock EFI one with PCV. Ray

calebessent · Post by **calebessent** » Sat Oct 27, 2007 8:32 pm

Ray, you're saying to restrict the hose that comes from the crankcase breather down to 3 mm?

Sounds easy enough.

-Cale

raygreenwood · Post by **raygreenwood** » Sun Oct 28, 2007 1:23 pm

Here is the gist of what you need and why. Having no PCV valve is better than having one (but still has issues). Having a PCV valve with D-jet causes "pulsing" with rich or flat spots. For those who say rubbish....and have never seen any problems.....I challenge that their D-jet is adjusted to the same loose and sloppy tolerances that the factory delivered it with.

And....by the way....when you have a tightly tuned system....its ugly noticable. Not having the PCV valve and going with a set orifice size.....is one of the main modifications you need to tune closer. The un-scheduled constant on/off vacuum leak of the PCV causes fluctuations in the MPS...which controls your fuel mixture. Since the ECU does not control the PCV valve...its a problem. The factory glossed it over by setting teh fuel baseline rather broad at the MPS. This is why all D-jet type 4's are so hard to set idle with by the idle screw...once you get actual fuel micture reasonable.

But....you must have crankcase ventilation. No argument. Having the straight nipple like in your picture also is too wide open. It also causes rich running and idle issues.

The easiest way to do this is with a 12mm piece of threaded rod about 19mm long. Use nylon threaded rod because its easier to drill...and use threaded rod because that way it is safely stuck tight in the 12mm hose (so it won't get sucked into the engine). Drill a 3mm hole in the middle. This is plenty large enough of an orifice for excellent crankcase ventilation.
I shows up to the MPS and the engine.....like a comination of the throttle being cracked open about 2* and the idle screw being open too far. But....that can be compensated for by a slight adjustment to the main load screw on the MPS....and about 1.5 turns in on the idle screw at the TB.
This mod actually finally makes the idle screw work properly. Since the orifice is constant...ether is no untimely, uncontrolled pulsing to screw with the MPS. Ray

wildthings · Post by **wildthings** » Sun Oct 28, 2007 5:53 pm

Ray's restricted hose goes between the breather and the plenum, not the air cleaner. I think you mentioned that you did not have a nipple on your plenum for this, that would be a problem. You are also going to have to install some form of ventilation hose between your rocker boxes and the clean side of your air cleaner for Ray's system to work correctly. If you can find the parts to install the original T4/Porsche system with a flame trap that would be best. On carburated engines VW apparently didn't think a flame trap was necessary, maybe they though going to the dirty side of the air cleaner was good enough. I think all FI engines had some form of flame trap.

raygreenwood · Post by **raygreenwood** » Sun Oct 28, 2007 6:53 pm

Yes...wildthings is spot on. But this is not very hard. 1.7 liter D-jet plenums should be a dime a dozen in most VW wrecking yards.....especially those for the automatic.

The connections to look for: from teh engine hatch forward...on the passenger side of the plenum:

12mm nipple closest to rear for the auxiliary air regulator
9mm nipple in between runners for automatic tranny connection.
TB opening

On the drivers side:
forward of the #3 runner
10mm nipple for MPS connection
threaded hole for air temp sensor
12mm nipple for airbox/PCV conection
On some cars....10mm nipple for the deceleration valve.

If you are crafty....you can get a bulkhead type fiutting with a ferrule that slips through a drilled hole from the inside and has a nut. Kinda rough on the airflow though.

If you remove the sheet metal over the heads you will see the bosses where the drillings go for the tubes.

Yes its great to have the flame trap...but really not necessary. Its peculiar...because there will never be anything but fresh air in that flame trap as it pulls from teh fresh side of teh air cleaner and flows to the heads. Ray