finding a leak in the vac system?

how do I find a leak in he Vacuum system? My XJ is stuck on Defrost vent setting and the search finds threads that say its a leak causing it not to switch modes...

where would I start to look for it? the canister in teh bumper looks to have no cracks... is there an easy way to find the leak?

ken

you're on the right track with that canister. pull out the entire hose-harness that runs to it and inspect every bit of it. it gets old and oil/time take their toll. as well as battery corrosion because it runs right below the battery. likely a break in the harness.

Look under the battery, battery splooge usually eats the hose right there. Another way is to spray some wd40, carb cleaner, sometimes even water with a mister type bottle on the hose system. With the engine running you will hear the idle change when you hit it with the spray.
I did our 89YJ one sat, did it one hose at a time, one elbow and tee fitting at a time. If I did it again I'd go park in the parts store lot and do it, sure would have had a lot less boxes of vac hose left over thats for sure.

The leak is in the harness, near the pressure bottle. This is the area near the relays and such. The cable rub a hole in the plastic vac line, as mentioned above, fog the area with something and listen.

Rev

Depending on the size of your leak you can get your ears near the area described in the previous posts with the engine running and then have someone turn it off, you might be able to hear air passing through the leak as you lose the vacuum stored in the tank for a second or two after the engine is off (and you can hear). I found a leak that way.

seymouj said:

Depending on the size of your leak you can get your ears near the area described in the previous posts with the engine running and then have someone turn it off, you might be able to hear air passing through the leak as you lose the vacuum stored in the tank for a second or two after the engine is off (and you can hear). I found a leak that way.

Click to expand...

It helps if you can hear a Mouse pissing on cotton.

I physically checked each and every hose and connection and put a red garbage bag twisty on each one that passed inspection.
I started with the vac can in the bumper and I used a 18" long, 1/2" dia piece of heater hose like a stethoscpope to "get my ear" up there...I heard it with that but not without.

I found one leak at the vac can and one at the manifold.

A vacuum gauge hooked up to the manifold, then take each line as it leaves the manifold and plug them one at a time. When the vacuum comes up, bingo.

Things people overlook, vacuum brake booster, EGR gasket, Intake gasket.