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Sun May 11, 2008 3:58 pm

Ok, I have some ideas on this, but I'd like a another opinion.

It's an 84 westy, and she's had a lumpy crap idle for the entire time I've owned her (about a year) During that time I've done all the replacements and tunings that the Samba Gods have advised, and for the most part the van is behaving VERY well.

Except idle, Warm/ Cold/ Tepid.. chug,chug,chug....chug.cchug.chug.chig.chug.

The breather hose seems to leave a very oily film post AFM around the engine (more than any of my past 80's german cars). Today while screwing around with timing and idle I decided that I'd focus on the dumb breather.
I squeeze the hose. Idle comes up to 1100 and SOLID.
AHAHA!! I think so!
I pull off the line, and use my thumb as a cork. I sniff the breather tube. stinky-ish, and a little smokey, more smoke comes with throttle tip in. But, this entire time my idle comes back down and sits FLAT and SOLID. -albiet, slightly high.

My theory is, I'm getting too much blow-by back into the intake post AFM. (o2 vs co2). The idle gets lumpy because I have cylinder that's leaking way more than the others, leading to a stray puff here and there. Compression itself doesn't seem that bad, as I can still drive it in Denver and the Foothills.

I haven't seen any mention to this on the samba, but can I just run a cork and a breather bypass? If I could, then I could set my timing and idle to be at spec, and maybe I could get this thing to be a bit better in tune.

Another interesting point is that this engine will continually seep a bit of oil from various bits on the bottom of the engine. UNLESS you open the engine to atmosphere, then it won't drip at all. (like pulling the oil filter)
Where's this excess pressure coming from? -even after sitting for two weeks.

Sun May 11, 2008 4:53 pm

The WBX motor is a sealed crankcase system. If you have any air leaks into the crankcase this will cause your engine to run lean. Bad valve cover gasket are the typical culprit.

Sun May 11, 2008 6:54 pm

so that would be a no-no on a open breather with a filter?

Sun May 11, 2008 9:41 pm

rhpaw wrote: so that would be a no-no on a open breather with a filter?

I like the idea as it would allow some clean air to move through the case helping to evaporate contaminants, but any air entering through the filter it is not going to be metered by your AFM. You might try orificing it down to 1/8 inch or so and see what happens.

Sun May 11, 2008 9:56 pm

The filter would be only on the crankcase side directly venting to atmosphere. The hole left in the intake boot would be corked.

If you gas it with the hole open post AFM, the engine chokes.

I'm wondering that with the additional crankcase "stuff" -non oxygen vapor being sent back into the system, that I seem to be running rich because there just isn't enough flamible O2 in the system to get stoich. -Even though the vapor volume is there within the combustion chamber.

It's crazy talk for me to bring up. But it was so obvious when I pinched that sucker when setting timing and idle today.
"crapa-crapa-crapaq-cc-crapa-crap..... VVVVVVVMMMMMMMMMmmmmmm"

Sun May 11, 2008 11:14 pm

Personally I think the VW engineers had their head up their asses when they designed certain aspects of the fuel injection and emissions system.

For instance, why would they tee in the carbon absorption canister into the vacuum lines controlling the distributor advance/retard?

I think the crankcase breather is also suspect. My doka is a Canadian model and has a heating element and a restrictor of sorts on the line. Don't ask me why? I don't know...

My digijet manual states:

"The breather valve operates via intake manifold vacuum. When manifold vacuum is high, such as at idle and during deceleration, the valve is closed as spring pressure on the valve seat is overcome. As manifold vacuum drops, such as at highway speeds, the valve opens to allow more vapors to be admitted into the intake manifold."

Sound like your breather valve should be disassembled and cleaned out.

Has anyone done this? Don't tell me that the damn thing can't be disassembled....

Also, this doesn't sound like a PCV (positive crankcase valve). Has anyone installed a PCV?

Another idea is routing the crankcase breather downstream of the AFM and Vacuum ports - directly into the intake manifold plenum in the center.

Keith

Mon May 12, 2008 1:49 am

If you look at how the breather is supposed to work, it should not cause the problems you see. It is more than likely coked up from years of bypass. You may try cleaning it with mineral sprits. Make sure you get a new o ring for the base, the old one will be hard as rock.

Mon May 12, 2008 9:55 am

The gases blowing past your rings should be pretty inert and will not change your intake mixture. If you have a vacuum leak into the case though, the extra unmetered air will cause a lean burn.

The improvement in crankcase ventilation systems during the late 60's reduced air pollution from automotive sources by about 20% while greatly increasing the life of a typical engine because the oil and engine internals stayed was so much cleaner. If you go back to using a draft tube, not only will you be adding to your local smog problem, but you will be shortening your engine life considerably.

Mon May 12, 2008 11:10 am

I cut the top off a tower just a few weeks ago because I just had to know what's inside. I wanted to know how much the breather contributes to excess oil consumption.

Here's the bits:

The diagram Dog provided is accurate. There is a diaphragm that is supposed to block the large breather outlet at high intake vacuum, by being pulled downward against a weak coil spring. There is a small orifice at the bottom of the elbowed outlet tube below it that would always allow a very small flow to get thru. The rest of it is just a baffled tower to allow condensed vapors to drain back to the sump, a liquid separator.

The problem is the diaphragm rots away, like the one in the photo, leaving the thing wide open at all times. Also, it's hard to see where any air is allowed above the diaphragm so it can move downward when there is a large pressure difference vs. atmosphere anyway.

I do think this could wreak havoc with your idle, as there are some combustibles (oil droplets, unburned fuel, and CO) mixed with the other junk in the crankcase vapor, and it's not at all unlikely that this is a contributor to the funky idle that a lot of the older motors experience. Obviously VW thought so, as they designed the system to keep all but a small bleed of vapors out of the intake during idle so as not to upset the mixture. I suppose they made it to open widely under low vac because blowby would be greatest with the most unburned HC under WOT and high load operation. I'll bet they also didn't want to ever pull a big vacuum on the crankcase as that would just encourage blowby and increase oil consumption.

WT is right, though, that if outside air is able to be drawn into the crankcase it could upset idle mixture if at the same time the tower diaphragm valve is not closing. I think the most likely source of air in that case would be the oil filler tube and/or dipstick tube. Judging by the rotted diaphragm in my specimen, I doubt that very many of these are still working as designed. Some kind of fix is in order.

Mon May 12, 2008 11:19 am

Well.. looks like my vanagon tax for May has been allocated.
VanCafe, here I come.

I can guarantee that's probably exactly what my million-mile breather tower looks like inside.

Thanks all, I would have never thought about atmosphere getting sucked into the crank.

Mon May 12, 2008 12:53 pm

10c,

It's cool to see what the inside of the breather looks like. I have always wondered what was hidden in there. I might put a breather on the list of improvements I need for my junker 84. With luck it might lower the oil usage a little, but hey, not ever bothering to change the oil because it uses so much has in some ways seemed like a benefit. I had tried stuffing the tower with SS wool to see if that would lower the oil usage, but it made zero difference.

Mon May 12, 2008 1:24 pm

We have big oil losses in the flat engines in aircraft. They will always blow the first two quarts out the breather in about an hour or so, the next quart takes about 3 hours. Several schemes to reduce the consumption have been tried, but the best involve a breather trap and return system. It is a labyrinth type arrangement that lets the vapors precipitate out on the sides of the spiral.

Of the two towers I had, one was bad. I never cut it open, it was obvious it didn't work correctly. Cool to see the innards. I wonder how many of these idle issues that everybody always assumes is the ECU or the AFM or throttle body are actually this POS, which has rotted away. Cleaning the one I did keep did improve its operation.

Mon May 12, 2008 2:40 pm

Yeah, mine blows thru the top quart of oil in no time, so I never top it all the way up anymore. Always leave it closer to the lower mark, never higher than halfway between. I also have an intermittent mainseal leak, gotta get in there and redo that, but it's going to wait 'til I have time to split the case to try out a different cam anyway. But that doesn't account for all the oil it really uses. I do see more than I'd like to see accumulating in the throttle body, so my interest was piqued in how that tower is supposed to work. Having a spare, out came the sawzall......

Not a bad design in concept, but terrible in execution. The diaphragm looks like a weird sort of rubberised fabric, and it's literally rotten. Of course you couldn't just do the diaphragm, because the whole assembly is glued together. Only a complete replacement is going to remedy this.

Quote: I wonder how many of these idle issues that everybody always assumes is the ECU or the AFM or throttle body are actually this POS, which has rotted away. Cleaning the one I did keep did improve its operation.

That's exactly what I've been thinking.

Mon May 12, 2008 2:49 pm

I have a new one in the mail. When it comes in I'll disect the old one and see how various things behave.
Right now my idle screw on the the TB is worthless.. you can either get the damn thing to run OR sputter+die. -no middle ground.

I'll report back in a week.

Mon May 12, 2008 2:51 pm

The other thing I've been wondering is whether it would work better, given the near certainty that the tower on my engine is as rotted as the one I cut open, by just routing the breather tube to the air cleaner inlet. You wouldn't want to drop it in after the filter, as the oily stuff would foul the AFM, but by letting it get filtered the droplets would be kept out. Vacuum there is pretty directly variable with rpm, so there would be little draw at idle, more at cruise, even more at WOT, kind of keeping pace with blowby production, I would think. The drawback would be going thru air filters much much faster, maybe too fast to be realistic.

Now that I think about it more, there's no vac to speak of in the intake elbow at idle, so it wouldn't actually do what they say it does anyway. The more i think about their design, the more f-ed up it seems to me.

Hmmmm.......

Mon May 12, 2008 5:21 pm

It doesn't look like a pcv to me. With a pcv, every time there is a crankcase positive pressure, it opens up to relieve the pressure.

So where do you guys think the breather tower should be routed? upstream or downstream of the vacuum lines, or upstream or downstream of the AFM?

Mon May 12, 2008 8:03 pm

A typical PCV valve arangement would probably work better. This kind of works the opposite way: when manifold vac is high, case venting is restricted, but opens when vac is low. Weird.

Mon May 12, 2008 9:21 pm

I can't say I really understand what happens on a Vanagon sealed crankcase system. Except for minor variations in flow all the blowby has to be drawn or forced into the intake air system at all times or the crankcase would see quite high pressures. If the pressure were allowed to climb then you would get oil puking out of every available crack, seam, seal, and orifice. What I think the valve may do is prevent surges in air flow from the case to the intake as the throttle opening changes and prevent the case pressure from dropping below atmospheric, in which case fresh air could be drawn through leaks in the case and mess up the idle intake mixture. I agree that a failed or failing blowby valve is a likely cause of bad idle and off idle performance.

I think the explanation in the page on Emissions Control that Dog posted is probably bunk. First off the valve never sees intake manifold vacuum, it sees vacuum up stream from the throttle valve not down stream. Second from looking at the pictures of the valve 10c posted it looks to me like the valve is most likely regulated by crankcase pressure and not be intake air system pressure. As I said above except for minor variations all the blowby has to pass into the intake air system at all times.

I wonder how the operation of the WBX valve differs from the operation of the valve used on L-jet fueled Bay window engines. D-jet and a PVC valve and carbs just had an open breather. I had always kind of assumed the the Bay window valve was just a backfire preventer, but now I question that.

Tue May 13, 2008 8:55 am

I'm thinking maybe I'll just get a regular PCV valve and fit it inline.

I have also been thinking about doing one of the liquid trap systems like Dog described. Lots of old timers used to bring the vapors to a canning jar to let liquids drip out. If I did this, I would fit my valve covers with vents, to get thorough breathing throughout. Common practice in the hi-po VW world anyway, and my engines put out quite a bit more power than stock anyway, which means higher cylinder pressures and potentially more case vapors as a result.

Tue May 13, 2008 9:16 am

hooray! Timely post for me! I have a 1983.5 Westy with a newish (10K miles) Gowesty 2.2 and have been pursuing a crappy idle for WEEKS! New plugs, wires (one failed resistance test), new cap and rotor, fuel pressure test, rebuilt injectors, all new vacuum lines, set timing,..... and nothing has had the slightest effect of the crappy idle. So for the past week I've been studying and tinkering the afm. Kind of interesting but I have lots of other stuff to do to get ready for my 5000 mile summer wander (I did buy this thing to drive around in).

I had the oil breather tower off and studied it and cleaned it. I concluded that it was just a bunch of baffles as no valve action was apparent. I looked thru Bentley and Samba (this site) and couldn't find much that was conclusive to do with the cc breather. In Bentley it does include a bit on pinching the breather hose as part of setting the idle CO (24.30).

So PLEASE post any info or conclusions you run into on this topic and I'll do the same.

TIA,
Charlie