Sounds useful. How about posting it here so others can benefit?

Tony, I'm on this. I'm putting the test together, and will report back when I have some info. Thanks!

DaddyGlenn - Tony has posted the vacuum leak testing "bible" - with pics - in several threads. Just do an advanced search on his user name and "CIS false air leaks" or something similar.

He is in no way hiding data. Just adding a personal touch with the PM/E-mail offer.

Cool! Thanks! I'll look for it. SmileWavy

Leaks!
 

I did the test today and found air leaking from the injectors. I get the feeling this is pretty common.

http://forums.pelicanparts.com/uploa...1318127568.jpg

The funny thing is that I went over the injectors carefully with the unlit propane torch and found no sign of a leak. And most of the injectors didn't show any leaking air until I jiggled the fuel line a little. 4 out of the 6 injectors did this, so I'm going to change the seals on all of them.

Can someone tell me what exactly you have to change to fix this leak? Is it just the injector O-rings, or is there more to it? Thanks.

The test was as thorough as I could make it, but not perfect. Some spots, like the intake pipe sleeves under the air box on the passenger side, are pretty tough to get to. I'll start by fixing the injector situation and see what effect that has.



DaddyGlenn - I'm happy to share info with you about how I did the test. I connected the clear air hose here to the brake booster outlet on the driver's side of the air box, attached the other end to a compressor, and injected between 5 and 10 psi of air. I sealed off the exhaust and intake, and used soapy water to reveal any escaping air.

http://forums.pelicanparts.com/uploa...1318128767.jpg

Oh and btw, there was quite a lot of air escaping from the edges of the air box and from the mixture adjustment screw on the fuel distributor. Since these are upstream from the metering plate, I considered them irrelevant to the problem, but I had plug these leaks (the nitrile glove in the top photo) in order to keep the pressure up and keep them from masking other more important leaks.

Subd.

While you're there.........
 

Danny,

You are on the right direction. Do you have a pop off valve installed? If you do, that will contribute to the mis-diagnosed scenario. A pop-off valve works well with the engine vacuum but not against a positve air pressure. This will open up at around 5 psi (positive air pressure).

The air box is the one causing you all these problem and headache. The air-box sealing plays a very critical role to your air mixture. So the test should include checking the air box too. Now, you have demonstrated that carb cleaner, starting fluid, unlit propane, etc. do not work as effective as your technique for detecting vacuum/air leaks.

Take your time in checking the air box for leaks. You have to confirm the absence of any significant air leaks otherwise you'll be back to square one. What air mixture screw air leak you are referring? This is outside the metering zone. Remove the air filter, cover, and the CIS intake rubber boot. Plug the hose and place a plastic glove on the throttle body and lower the air pressure. Keep us posted.

Tony

This is some of the most useful info for my "tool box of knowledge" that I've found in quite a while.

Thanks!

CIS going to the dumpsters........
 

This is probably one of the main reason why people dumped their CIS for other system. The frustration and the lack of understanding how a simple system could be checked and maintained by DIY'ers like you or me. While switching to another system is a choice by an individual based on his liking or desire, most lost their trust in CIS due to lack on understanding how the system operates. And adding to the confusion is the difficulties of troubleshooting CIS using guess-work.

Tony

Glenn - thanks should go to Tony for inventing this technique. I just pieced it together from comments on different threads, and photos from Tony that Scott.k emailed to me. I tried it first with a bicycle pump and no seal on the exhaust pipe. That was good exercise.

Tony - I'll try it again with the intake boot removed. I think that will cut out some of the 'noise'. when I say 'air is escaping from the edges of the air box' I mean it's coming from the space between the air box cover and the lower housing, which should be sealed off by the orange rubber gasket around the air filter. The adjusting screw I'm referring to is the one in the crevice between the intake boot and the fuel distributor. It's accessed via a little hole, and the air comes up through there. But as you say both of those spots are outside the metering zone, so they shouldn't be affecting the fuel mixture.

I did notice that a rubber sleeve on one of the intake runners is missing its hose clamps (where it connects to the airbox). I didn't find any leaking air there when I tested it with soapy water though. It's the one at the very bottom so it'll be a PITA to get to.

subd

The technique consists of plugging exhaust, air inlet, soapy water on the possible "exits" and blowing compressed air at the airbox ?

Yup. Not 'at' the airbox, but 'in' it, via ... wherever you like i guess, but the brake booster port is a convenient spot. 5 psi should be enough acc. to Tony. the rubber gloves are nice for sealing off the intake and exhaust (see pictures above) because they puff up to show you have pressure, and if there's too much pressure they'll just pop off.

Here are the parts inside the injector ports.

There are machine made crimps on the intake runners that hold the orange/terra-cotta colored pieces in. If you want to replace those and their o-rings, you can dremel the crimp lips off before removing the sleeve and re-punch the crimps back in with a drift/center punch after the new parts are installed.

Here is a link that may assist. I had the luxury of having the engine out when replacing mine.

81 911 SC Fuel Injector Replacement Question - Rennlist Discussion Forums

http://forums.pelicanparts.com/uploa...1318290493.jpg

update
 

Finally got a chance to work on this over the weekend. I replaced the sleeves and O-rings on 5 out of the 6 injectors. The one on cylinder #6 was too tough to get to, and I'm planning on dropping the engine this winter anyway so I can pull it then. Everything was baked solid and probably original to the car. Not one of the injectors would come out without taking the sleeve with it.

Big improvement! Car is much happier in the first 15 minutes or so, and runs smoother overall. Also a big reduction in the soot buildup on the back of the car, so it seems to be running leaner. Fuel mileage is up too. Still a little cranky when cold but not nearly as bad.

Next step is to address the fuel mixture, HOWEVER I'm not really certain I've gotten all the leaks. I can't see how to get to the stuff on the back side of the engine, or under the airbox on the 4-5-6 side. Guess a mirror would help. But for now I'm enjoying the change.

Just wanted to bump this thread one more time to say thanks for all the help, especially from Ossiblue, Tony/Boyt911sc, and Bob Kontak. This issue fell onto the back burner when I realized I would have to drop the engine to fix the clutch. Now that the engine is out it seems a lot easier to be 'scientific' about finding CIS leaks. I just started a new thread about it. Cheers and thanks again, D

The smoking gun!
 

... or at least one of them. a badly installed pop-off valve. There are two big gaps in the epoxy that are letting air blow by the side of the 'toilet seat'.

http://forums.pelicanparts.com/uploa...1327517794.jpg

It was much easier to find this with the engine out. Same goes for the cracked vacuum hose behind the rubber boot on top of the air box. Also, taking off the air filter lid and the rubber boot helped to isolate the critical parts of the system.

http://forums.pelicanparts.com/uploa...1327518241.jpg

Engine test stand for Pelican members.....
 

Areaman,

Your engine would look like this if you have a test stand (home-made contraption):

http://forums.pelicanparts.com/uploa...1327546170.jpg

http://forums.pelicanparts.com/uploa...1327546195.jpg

You are doing good. With the engine out, you have 360° access to your engine and finding the illusive air leak would be very convenient. I had a guy from Madison, WI drove all the way to my place with his engine in their family mini van. We're talking about 11 hours drive and over 1,000 miles. Here is a picture when he went back home with his motor.
http://forums.pelicanparts.com/uploa...1327547128.jpg
Tony

Very cool! Was there an original frame that you started with, or did you just weld it together from scratch?

I hate to interrupt this thread but I would like to get back to the WUR adjustment. sorry but I could not better information this thread has already been started.

In this video it shows the guy making an adjustment from the bottom of the WUR:
k-jetronic adjusting warm-up valve, system & control pressure on golf mk2 gti - YouTube

I have seen this adjustment conversion in other places (I thought Bruce Anderson wrote about it). What exactly id this for and how does it differ from the other adjustments that have been discussed?

The problem I have right now is I can get the cold pressure where I want it, or the warm pressure, but not both at the same time. I have not tried to adjust the the disc yet. My WUR is also modified to be adjusted from the bottom and i wonder if that is a better way than knocking on the disc?