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Late FI Bus EEC Valve Fix
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Amskeptic
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PostPosted: Sun Aug 14, 2011 10:59 am    Post subject: Late FI Bus EEC Valve Fix Reply with quote

This is a commonly overlooked failure in the late fuel injection buses that happens to steal all of your vacuum advance as well as increase the smell of fuel vapors in the engine compartment.

The EEC valve was an evolution of the technology required to trap fuel vapors from the fuel tank. Since 1970 or so, Volkswagen merely plumbed the fuel tank vapors to a charcoal canister that was force-fed fresh air from the fan and dumped its vapors into the air filter any time the engine was running. Unfortunately, the need to reduce hydrocarbons rendered this simple system inadequate, particularly after a heat soak where gas vapors just spiked those HC emissions through the roof and made the car run too rich when first started.

VW decided to meter the fuel vapors into the engine through a valve, the EEC valve, so that these extra HCs would only be added during high airflow periods, and what better time than at full vacuum advance? A tee off the vacuum advance hose pulls the EEC valve diaphragm from its spring-loaded seat, thus allowing fuel vapors from the canister to enter the air filter body.

Problem is that fuel vapors and rubber diaphragms don't get along too well, and the diaphragm gets dried out and brittle. When it leaks, the vacuum advance vacuum signal disappears. To test, remove the vacuum hose to the EEC at the tee and apply vacuum to the hose. This looks odd and unsettling to the casual passer-by. It should hold, and you can sometimes hear the diaphragm clunk. If it just passes air, well, try this procedure:

1) Remove air filter cover by releasing the clips and pulling out of the engine compartment. You can leave the AFM side of the air filter in. Place on a counter, VW thoughtfully provides one just above the engine. With several small flat-bladed screwdrivers, gently pry the outside ring of the plastic housing out from the inner circle of the EEC valve, You will see six or so plastic tabs cast into the plastic housing that snap the circle in place. Be nice here. Work it. Pry and pry, just get things loosened up a bit. Do not turn the screwdrivers as this will make it look like beavers have been chewing in there. After you have gotten irritated, focus on one side of the circle and get the screwdrivers all lined up and go for the final snap-out free push. I found three screwdrivers all pried simultaneously on one side finally released the inner circle.

2) Repair the diaphragm:
Image may have been reduced in size. Click image to view fullscreen.

Like a speaker, it has an outer suspension "gutter" where you will find cracks and maybe a split. Clean off the glycerine that VW hoped would protect the rubber. I used carb cleaner and a paper towel. Dry thoroughly. Smear a thin layer of Permatex Ultra-Black RTV into the gutter all the way around the circle. Work quickly so the RTV doesn't start to set and pull up with your finger. Keep it thin but contiguous. Clean any excess RTV off the outer perimeter where it sets in the housing, this is important for a vacuum-tight seal. Allow to set for a full 24 hours. Clean the housing making sure the diaphragm seat is perfectly smooth both where it contacts the openings and at the perimeter.

3) Set in the opening flat center facing down. You can see the repaired area:
Image may have been reduced in size. Click image to view fullscreen.



4) Place the plastic disk on the diaphram with the spring seat facing up.
Image may have been reduced in size. Click image to view fullscreen.


Here it is just sitting there, waiting for a spring:
Image may have been reduced in size. Click image to view fullscreen.



Look, there is the spring, now:
Image may have been reduced in size. Click image to view fullscreen.


5) Now carefully clean the perimeter of the valve housing where it is going to snap in the air filter housing. Use a patented IAC razor blade technique to make a perfectly square edge that is smooth all the way around the perimeter. Use a light coating of grease on the valve where it will contact the diaphram and along the edge so it will snap under the moulded clips of the air filter housing:
Image may have been reduced in size. Click image to view fullscreen.


Press the valve housing over the diaphragm/plastic disk/spring (with the word "Knecht" facing directly towards the canister nipple, if you care about such things):
Image may have been reduced in size. Click image to view fullscreen.


Test for vacuum. It should now hold. Reinstall air filter housing making sure you have a perfect seal between the filter media and the cover as you snap down the four clips. Reinstall the charcoal canister hose and the vacuum hose from the vacuum advance tee. Now you can test with a feathered throttle at 3,000 rpm to see that you get 36-40* vacuum advance.
Colin
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Hoody
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PostPosted: Sun Aug 14, 2011 2:47 pm    Post subject: Reply with quote

Awesome! Thanks Colin!
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Whitley
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PostPosted: Sat Jan 14, 2012 7:45 am    Post subject: Reply with quote

While getting ready to swap in a fresh engine, I recently pulled apart my EEC valve and found a hole in the diaphragm. I attempted a fix with some rtv, but I can't imagine it holding up long under real conditions.

Since the function of the valve is pretty straight forward, and the diaphragm is NLA, I'm wondering if a simple EGR valve or other vacuum controlled valve could be used on the air cleaner for a more permanent fix.

It seems silly to buy a bunch of OG air cleaners in hopes that one has a good diaphragm in it. This is a tricky and I assume very common place for a vacuum leak, so it seems we are going to have to get creative.
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PostPosted: Sun May 06, 2012 6:31 pm    Post subject: Reply with quote

Can a faulty EEC diaphram be one cause of lean mixtures?
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PostPosted: Sun May 06, 2012 6:45 pm    Post subject: Reply with quote

Yes. Pull the vacuum line off your EEC while the bus is running, and plug it with a golf tee. Your RPM's will likely drop as there will be no excess air entering the system.

The EEC air is not yet metered as it is pre AFM, so it is the same as a vacuum leak.

To test your EEC, suck on it like a straw. It should lock shut and not allow you to draw air in. If it lets air in, then it is a problem in need of repair.
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PostPosted: Sun May 06, 2012 11:07 pm    Post subject: Reply with quote

there is a fellow on Ebay who sells both repop EEC and S-boot.
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PostPosted: Mon May 14, 2012 11:11 am    Post subject: Reply with quote

I checked my attempted repair to the EEC diaphragm- it was leaking so I plugged the vac line to it, and found out what a properly advancing distributor does for the engine- wow. I have tried to find the guy on ebay that sells replacements to no avail. Are there any other leads of where to get the diaphragm? Mine is ripped in a spot that will never hold any adhesive.
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PostPosted: Mon May 14, 2012 11:43 am    Post subject: Reply with quote

Whitley wrote:
I checked my attempted repair to the EEC diaphragm- it was leaking so I plugged the vac line to it, and found out what a properly advancing distributor does for the engine- wow. I have tried to find the guy on ebay that sells replacements to no avail. Are there any other leads of where to get the diaphragm? Mine is ripped in a spot that will never hold any adhesive.


This is the seller.
http://myworld.ebay.com/sell2ship/

Contact him to see if he has any left.
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PostPosted: Mon May 14, 2012 9:51 pm    Post subject: Reply with quote

I just love all of these informational segments. thank you for taking the time to document these fixes. Very very helpful.
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PostPosted: Tue May 15, 2012 7:59 am    Post subject: Reply with quote

Thanks for the tutorial Amskeptic. I have been trying to track down a fuel smell while driving and having no luck as of yet, but I stumbled along this thread yesterday.
I checked mine and sure enough it leaked and the other I had in my basement leaked as well.
So I bought some Permatex black silicone adhesive/sealant and carb cleaner. Cleaned the rubber applied the adhesive over the cracks and let it set for 24 hrs.

Worked like a charm. I now have a spare as well. Thanks again.
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PostPosted: Tue May 15, 2012 7:20 pm    Post subject: Reply with quote

Ditto. Pulled my 79 that was superglued together. there was a pencil lead sized hole in the diaphram and I RTV'd both sides and put it together. Tomorrow I will hook up the proper vac hoses and retime it.

Then it after the hight CHT temps. Wish me luck.

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PostPosted: Mon May 28, 2012 11:44 am    Post subject: Reply with quote

I ordered what I thought and was told was the EEC Diaphragm for my 76 from the ebay seller, but as you can see they are not the same.
Image may have been reduced in size. Click image to view fullscreen.


The one on the right and the little spring is what my bus has. Does anyone know what the diaphragm on the left is for?
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PostPosted: Mon May 28, 2012 11:51 am    Post subject: Reply with quote

Whitley wrote:
I ordered what I thought and was told was the EEC Diaphragm for my 76 from the ebay seller, but as you can see they are not the same.
Image may have been reduced in size. Click image to view fullscreen.


The one on the right and the little spring is what my bus has. Does anyone know what the diaphragm on the left is for?


It is also an EEC diaphragm, but......

The small EEC diaphragm was an earlier variation and was oriented on the airbox for a convenient connection to the charcoal canister on the back firewall. The big diaphragm is for a slightly later airbox in which they re-oriented the connections and expanded the the diaphragm for a charcoal canister mounted beside the passenger side taillight. You could switch quite easily to a later airbox, and use the new diaphragm. Let me know if you find a source for the small diaphragm, as my wife needs one. We are using a later airbox right now, but I would like to switch her back.

Essentially, the small diaphragm airbox and the big diaphragm airbox can be switched easily: plug and play. The only issue is that the clear connector hose gets hard and does not want to change its shape for the new configuration, so you may need to replace it, or heat it and re-bend it. You'll also need to re and re your AFM.

If you don't want the big diaphragm, and the price you paid was reasonable, I will buy it from you, for what you paid, and keep it for the day when I need it. That is if returning it is not an option for you.
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Last edited by Westfabulous on Mon May 28, 2012 11:58 am; edited 1 time in total
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PostPosted: Mon May 28, 2012 11:57 am    Post subject: Reply with quote

Thanks Westfabulous - I just sealed up the current EEC portion of the airbox (a old fashioned canning lid fits perfectly in the recess) and will start searching for either a later airbox or an earlier diaphragm. Fixing the vacuum leak it caused finally got my distributor advancing correctly, so I'd rather leave it sealed up and have a few fumes than not have a functioning distributor.
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PostPosted: Mon May 28, 2012 12:00 pm    Post subject: Reply with quote

Whitley wrote:
Thanks Westfabulous - I just sealed up the current EEC portion of the airbox (a old fashioned canning lid fits perfectly in the recess) and will start searching for either a later airbox or an earlier diaphragm. Fixing the vacuum leak it caused finally got my distributor advancing correctly, so I'd rather leave it sealed up and have a few fumes than not have a functioning distributor.


You can disconnect the EEC vacuum line and plug it with a golf tee, and drive on, until you sort it out. It will ensure that you hold vacuum for your mechanical advance.
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PostPosted: Mon Jun 25, 2012 11:00 am    Post subject: Reply with quote

Great write-up! I took mine apart (real PITA I might add) and there was a 1/2" slice in the rubber "gutter". I smeared on the RTV, waited a day and started it up. Runs well!
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Last edited by Vamstad on Mon Jun 25, 2012 11:50 am; edited 1 time in total
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PostPosted: Mon Jun 25, 2012 11:03 am    Post subject: Reply with quote

my 1977 had the larger style EEC.
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Caveat: I am not telling you what to, or what not to do. When a suggestion is offered, it is wishing you the best, and is based on my experiences as a mechanic, automotive machinist, and from racing in the era your bus came to life. I love winning but now I figure it is your turn. My goal is only to share what has been learned on my path. Smile

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PostPosted: Thu Dec 27, 2012 3:57 pm    Post subject: Reply with quote

I bought a good used one here off of TS but unfortunately it is also failed:
Image may have been reduced in size. Click image to view fullscreen.


im going to try the same RTV fix.

how have the others you have fixed held up?
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PostPosted: Thu Dec 27, 2012 4:23 pm    Post subject: Reply with quote

Chris, I guess we have just been lucky. You might keep your eyes open for any bay filter housings and just swap out that . I know that one I had did not like being taken apart to see what was in it.
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Godspeed to all who undertake a journey in a VW Bus. You only get one shot at life - go out and enjoy it - let the Light shine.

Caveat: I am not telling you what to, or what not to do. When a suggestion is offered, it is wishing you the best, and is based on my experiences as a mechanic, automotive machinist, and from racing in the era your bus came to life. I love winning but now I figure it is your turn. My goal is only to share what has been learned on my path. Smile

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1977
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PostPosted: Thu Dec 27, 2012 6:09 pm    Post subject: Reply with quote

airkooledchris wrote:
I bought a good used one here off of TS but unfortunately it is also failed:
Image may have been reduced in size. Click image to view fullscreen.


im going to try the same RTV fix.

how have the others you have fixed held up?


I was skeptical, but if you use exactly what Colin spec'd in in tutorial, it will work like a charm.....and I don't mean a half-assed repair. It really does work wonderfully and is very flexible and forgiving, and Mrs' Westfab's EEC is as new again. No need for a new diaphragm, unless you really want one.
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