Tips on looking for air leaks?

[ngc414]

Im still trying to get my idle issues fixed. Next on my list is to search for air leaks. At this point its like finding a needle in a haystack. Does anyone have any good tricks for finding air leaks?

[cgarr]

A little shot of carb cleaner around the suspect areas will change the idle if there is a leak.

[dlagerstrom]

I posted in your original thread about the areas you want to check. Is the airbox cracked? It will be underneath and hard to see. All of the vacuum lines, even the one that goes to the brake booster will need to be checked/replaced. The boots that connect the airbox to the intake runners. The orings around the injectors and the second o-rings around the injector insulators. The insulators themselves may be cracked. Many places to check before you start spraying carb cleaner or using some un-lit propane. I would guess you have some major leaks and you will find it difficult to notice the idle change with your system in its current state.

Check into it and let us know what you find.

[crustychief]

the lines in back of the airbox on the right side of the car really get brittle from the heat mine crunched like potato chips

[ngc414]

Originally Posted by dlagerstrom

I posted in your original thread about the areas you want to check. Is the airbox cracked? It will be underneath and hard to see. All of the vacuum lines, even the one that goes to the brake booster will need to be checked/replaced. The boots that connect the airbox to the intake runners. The orings around the injectors and the second o-rings around the injector insulators. The insulators themselves may be cracked. Many places to check before you start spraying carb cleaner or using some un-lit propane. I would guess you have some major leaks and you will find it difficult to notice the idle change with your system in its current state.

Check into it and let us know what you find.

I looked it over earlier and did notice what appeared to be a possible crack on the driver side of the airbox. Its on the seam area so it is tough to tell if it is a crack or the way the box is molded. I put a small amount of rtv sealent along the area that looked cracked. When I start the car tomorrow i will see if there is any difference. Now that I read your post, Im thinking that a cracked air box might be the problem.

[ngc414]

I discovered that many of the flat head scerw in the air box around the pop off valve area are loose. I went to tighten, but several of them are stripped. I am going to try a slightly larger screw and see if I can tighten it up.

[ossiblue]

I have been following your posts on the CIS as I have had similar problems in the past. The CIS system is truly more than the sum of its parts and it can be frustrating to try to fix. You are doing a good job of finding out the relationship of the different components.
The only thing I haven't heard you do is a pressure test of the system. IMO, you should do that asap--it is easy and if your system pressure and control pressure (warm and cold) are out of specs, that needs to be taken care of before any adjustments to the enrichment.
The possible air leaks are numerous, as you know. Keep at it and get familiar with all hoses in the engine compartment and don't assume any are sound without actually checking (and don't forget the unseen hoses between the engine and the firewall!).
Keep at it, good luck, and let us know what you find.

[ngc414]

That was going to be my next question. In the past with turbo cars I have an adapter that fits into the intake hose with an air fitting. I would pressure up the system and listen for leaks. It made finding leaks simple. Is there an adapter for the 911sc? Is there a procedure for the best way to pressure up the system? Thanks for all the help.

[gtihop]

I used a smoke machine for mine to find leaks. Hooked it up to the intake boot to the throttle body. I was amazed- leaks around 4 injectors, airbox seam. Very easy to use and find vac leaks.

[LM3929]

To save your face hair, take an old propane torch valve with bottle and attach a length of plastic tubing with a piece of 1/8" brake line tubing, cover the tubing with shrink tubing (guess why) and you have a leak tester that unless you leave it running in your garage is not as volitile as carb cleaner or eather and you can direct the flow of propane to various area rather that flood the area.

Lornwe M.

[ngc414]

Originally Posted by gtihop

I used a smoke machine for mine to find leaks. Hooked it up to the intake boot to the throttle body. I was amazed- leaks around 4 injectors, airbox seam. Very easy to use and find vac leaks.

Where did you get a smoke machine? Do they rent them?

[gtihop]

have one in the shop at work. Find any shop that does diagnostics and they should have one. shouldn't really take more than 1/2 hour to hook it up and find leaks. snap on make the machine.

[ngc414]

The fitting I had from my 300zxTT fit the 911 TB perfect. Basically a molded piece with a guage and air fitting. here is a pic. I set my compressor at 5psi and shot a little air into it and it held nothing. It didnt even build any pressure I tried again with 10psi and same result. It should hold pressure correct? maybe I am missing something or I have a huge air leak somewhere.

[beepbeep]

Where did it leak? When I do "pressure test" I usually run my fingers around all hoses and feel for rush of escaping air.
Usual culprits: injector seals, intake/head gaskets.


Make sure you block the crankcase ventilation if you connect air north of it. You want to pressurize intake, not the whole crankcase as it will only blow into oil tank.
Cams with lot's of overlap will blow air into exhaust so you might want to block the exhaust as well. Pop-off will leak too.

[Jim Williams]

This hopefully be something you will have already noticed and blocked off, and that would be your pop-off valve. They hold vacuum but not positive pressure.

[ngc414]

Originally Posted by beepbeep

Where did it leak? When I do "pressure test" I usually run my fingers around all hoses and feel for rush of escaping air.
Usual culprits: injector seals, intake/head gaskets.


Make sure you block the crankcase ventilation if you connect air north of it. You want to pressurize intake, not the whole crankcase as it will only blow into oil tank.
Cams with lot's of overlap will blow air into exhaust so you might want to block the exhaust as well. Pop-off will leak too.

Where is the crank vent?

[LM3929]

If you look in the Porsche Technical Bulletin manual Nov. 48 to Dec 85, they show how to make the testing plate.

LM

[ngc414]

Originally Posted by LM3929

If you look in the Porsche Technical Bulletin manual Nov. 48 to Dec 85, they show how to make the testing plate.

LM

Could i find that online?

[LM3929]

don't we all wish that were true, but I have a copy............somewhere, as soon as I can find it I will post it later tonight.

LM

[ngc414]

Originally Posted by LM3929

don't we all wish that were true, but I have a copy............somewhere, as soon as I can find it I will post it later tonight.

LM

Thanks.