Vacuum problem?

[Scylla]

Hi fellow bussers

Please go easy on me with this and forgive any inaccurate terminology as I am simply repeating what I have been told..

My 2.0FI has had a problem of starting up ok, idling, but then cutting out when any gas was applied. We've now had the fuel tank out and cleaned, which I'm very pleased about as it was full of rust, but the problem persisted. Then my mechanic friend who's been helping me out, but who has no specific VW experience, found something: if you pull up on the airflow meter the engine cuts out. He says he thinks there may be an air/vacuum leak, and wants to know if there should be a seal between the inlet manifold and the throttle body?

I hope some of the above makes some kind of sense.

If not, are there any checks we can carry out to search for a leak in the system?

Thanks a bunch

Damian

[Gypsie]

Check the connections between the AFM and throttlebody (or whatever it is called for FI) as well as Throttle body to intake plenium (the fat fourlegged spider on top) with wd40 or some other spray (gumout carb spray) to see if there is a noted vacuum leak as it sits. (idle will change as the spray material is sucked in and distributed to the cylinders.
Then do some AFM movement testing. Make it die in the way you found the fault before. can you lift the afm and it doesn't die, just sputters and koffs....let go and see if it evens out. We are looking to see if the s-boot has a crack that is creating a vacuum leak. Gentle now don't get all crazy tuggin' on it....

The vacuum leak may get more pronounced as the engine heats up.

You also want to make sure that the vacuum leak being created (at the core of this hypothesis) is AFM related and not something else that is being moved when the afm is being moved. (ie the intake runners that connect to the head) Spritz the spray to all areas where a vac leak can occur (there's a dozen or so).

If you can get the AFM out and remove the S-boot, inspect it closely. if you see the connections holes (from AFM, to TB, from crankcase, from Aux air/decel) are cracked or you find a crack in the boot you may try to coat it with an RTV or Tool coating product. I think there have been some successes with coating the whole boot with this material to create a fresh, sealed unit.

Maybe the 'cut out' is electrical in nature so make sure that the AFM Harness connection is firmly seated.

2cents

PS-Pix of the sboot and such

[vwlover77]

What Gypsie said, but I'm guessing there's a big ol' split in the "S-boot" that opens up when you bend it. Or, one of the hoses is split and opens up when you move things around.

[Scylla]

Thanks very much for the replies - I forgot to add that the air filter is bending the faulty part out of shape - when we remove the air filter it runs fine. Does this point to anything in particular?

Also, can anyone say what seal should exist between the inlet manifild and throttle body - is it a rubber o-ring or similar?

Thanks again - will be following all this up when I get back to the bus tomorrow morning.

Damian

[vwlover77]

There is a special rubber gasket between the throttle body and the intake air plenum. See the link below:

http://www.germansupply.com/home/custom ... 388&page=1

Are you saying that when the AFM is free to hang in the air, not attached to the air filter box, that the Bus runs correctly? If so, I would suspect the S-boot once again, or the wire harness that plugs into the AFM.

[vdubyah73]

There is a special rubber gasket between the throttle body and the intake air plenum. See the link below:

http://www.germansupply.com/home/custom ... 388&page=1

Are you saying that when the AFM is free to hang in the air, not attached to the air filter box, that the Bus runs correctly? If so, I would suspect the S-boot once again, or the wire harness that plugs into the AFM.

That seal is still available at your local VW dealership. used until '92 or so on Synchro's . $6 a couple years ago

[Scylla]

Sorry to resurrect this thread but the bus has been off the road since my original post, and now that I'm trying to get it up and running again, of course it still has the problem.

Am having trouble sourcing the parts mentioned in the replies. I can't find an intake air plenum or s-boot on any of the UK sites, although my local VW dealer still holds the gasket mentioned by vwlover77.

Is the s-boot actually part of the AFM, or is it a separate psrt? And is a plenum the same as an air intake manifold?

If anyone can suggest alternative part names to assist me in my search I'd be very grateful, or if you know of a USA site that stocks what I need, I'll be willing to import.

Thanks again

Damian

[Randy in Maine]

Intake boot = S boot

The "intake runners" are the 4 pipes that go to the heads from the air plenum as described below...you can see the 2 left ones in gray here. They have hoses that attach them to the the air plenum. If yours are leaking or don't fit well, get some new ones.



Send Scott at German Supply an e-mail. He may be able to get you a new seal that goes between the throttle body and the intake plenum.

[Scylla]

Just a word of thanks for the very helpful replies - the problem is indeed a big old split in the s-boot. Randy, thanks for the suggestion, Scott at German Supply has a secondhand one for sale. I really appreciate this, have been unable to source one anywhere in the UK.

Best

Damian

[Randy in Maine]

Until that replacement S boot shows up, we sometimes repair a torn one with something here called "Sho Goo" (sort of an RTV sealant used to fix tennis shoes). You want something that actually sticks and is able to flex some.

You might give that a try.

[Scylla]

Thank you Randy, I'd like to try that. Have found some shoe goo... Is the s-boot easy to remove and put back for someone with no experience, or shouls I pay the mechanic?

[Randy in Maine]

You can do this.

Remove the aircleaner and lay it aside. GENTLY remove all of the fittings that plug into the S boot and note where they are supposed to go. Remove the S-boot from the clamp at the throttle body. I would clean it inside and out the best I could.

Those fittings that attach stuff to the S boot need to make a nice tight seal. Sometimes they need a wrap of electrical tape and a plastic "zip tie" to hold them nice and secure and to not make them leak your precious vacuum.

While you are in there, remove the throttle body and examine that seal between the TB and the air plenum and see if it is a vacuum leaker. If so, you are going to have to make it quit leaking. I bought a seal from German Supply quite a while ago, but they may be available. Tighten those 2 screws evenly to it mounts well.

Keep us posted with progress.