how to use a smoke machine to find vacuum leak

[Richard R.]

69 L46, 4 speed.
I am preparing for a PV in a month and struggling to find vacuum leaks. PV test says the headlight doors should be able to be closed 2 - 3 minutes after the engine has been shut off. I knew I had a bad leak since the engine was running rough, stalling etc from time to time. Using an electric vacuum pump I found a leak on the headlight override switch under the dash and replaced that. Currently the headlight doors will close 1 minute after engine shut off, but not after 2. Engine runs great. But still leaks to find. I have read in several threads that a smoke machine can be real helpful in locating leaks. I got one last week and started to use it today. It has a pump internal to the bugger and does make smoke. Yet, when I connect to the system (after the check valve and with the heat control system isolated out) there is no leaks showing. I am wondering if I have to vent the system to allow the smoke to circulate? Any suggestions will be appreciated.

Thanks,

Rich

[Mark E.]

Re: how to use a smoke machine to find vacuum leak

Connected to the main supply line past the check valve, smoke should reach past the reservoir tank to the valves.

To check the lines from the valves to actuators, you may need to remove the line from the valve and pass smoke from there.

Also check the control lines that go through the firewall. Operate the light switch, wiper switch and bypass switch through all positions.

For the HVAC, connect from its supply line under the hood, then move the wheel through all its settings.

[Richard R.]

Re: how to use a smoke machine to find vacuum leak

got it. I have got the smoke to go through the hvac. I didi move the wheels through all the settings. Nothing showed in the interior, which I am thankful for! Getting back to it tomorrow after getting "sucked" away on something else.

Rich

[Mark E.]

Re: how to use a smoke machine to find vacuum leak

got it. I have got the smoke to go through the hvac. I didi move the wheels through all the settings. Nothing showed in the interior, which I am thankful for! Getting back to it tomorrow after getting "sucked" away on something else.

Rich

Please post your process, results and lessons learned. It's a good way to diagnose the C3 vacuum system.

[Edward J.]

Re: how to use a smoke machine to find vacuum leak

Rich, you may want to remove the hoses for headlight actuators and smoke them I think the hoses are red and green. If you smoke one side and see smoke coming out the opposite side hose the diagram has a leak, also note the actuator rod boot than can leak to. You can also do the same with wiper door actuator.Marks test will pretty much test all the vacuum supply hoses under hood. What ever your leak is it a sounds very small, good luck. Also before you go wild looking for a small leak you can also get in touch with the team leader and ask him if your time frame will work for your PV. I thought I heard something about 20. Seconds. Maybe way off base.

[Richard R.]

Re: how to use a smoke machine to find vacuum leak

I'll check out the headlight actuators probably tomorrow. I found, using smoke, that I still have a leak around the rubber gang connection at the override wiper door switch. arrgh. I thought that the wiper door relay was bad - no smoke leak but the vacuum test I did first indicated it didn't hold vacuum. Then I removed it to check again and realized the wipers were parked and pushed the button down, like it's supposed to, but it invalidated the test. It is fine.

The smoke machine i got uses baby oil and I don't like that it leaves an oily residue inside the lines, especially at connections.

The hunt continues.....

[Mark E.]

Re: how to use a smoke machine to find vacuum leak

The smoke machine i got uses baby oil and I don't like that it leaves an oily residue inside the lines, especially at connections.

The hunt continues.....

Good input by Edward.

I never noticed nor checked for oily residue, but that makes sense. My first thought is this may be good for the valve, switch and actuator seals. But who knows how baby oil reacts with these? It's probably a good idea to keep an eye on the filter for awhile as vacuum draws in the oil with use.

[Richard R.]

Re: how to use a smoke machine to find vacuum leak

Update on the hunt.

using a vacuum gauge on the headlight actuators reveals a leak down from the front port/headlights open. I lose vacuum from 15 in less than two minutes on both sides. The rear port/headlights closed holds vacuum perfectly. I have a call into the fellow who restored these for me to see what he suggests. Perhaps the seals can dry up from not using it? Also, the wiper door actuator leaks/loses vacuum on both closed and open sides. That's not helping either. In all these cases I connected the might vac directly to the device, and bypassed any connections. All other engine bay components tested properly.

To pass PV, the headlights are opened with the engine running and then the engine is shut off and the stop watch starts for 2-3 minutes until the headlights can be closed. I'm guessing the actuators are my biggest issue since they only leak on open.

To check connections, I did run smoke through various vacuum circuits and only problem so far is the overide switches/rubber gang elbow connections.

[Richard R.]

Re: how to use a smoke machine to find vacuum leak

another update, getting closer!

The two headlight actuators were repaired. Advice from Mr Demmel was a great help! I put RTV sealant around the boot seal that is under the dust boot cover, in two places - where it plugs into the can and on the shaft indentation for the top part of the boot. That fixed one right up! The other continued to leak and discovered (again thanks to Bob) that it was leaking around the metal ring that holds the inner seal and is stamped into the can. Super glue dribbled around that ring sealed it right up. Holds vacuum nice now. Reinstalling them back in tomorrow.

The wiper door actuator unfortunatley won't hold vacuum regardless of what I do and is probably a bad diaphragm. It's going out in tomorrow's mail for repair.

What I am learning from all of this is a requirement for a systematic check of all components in the system, the lines and the connections. Smoke has helped with the later, but the components require a leak down check with the mighty vac.

[Grahame M.]

Hi Richard,

This is a very timely thread for me as I've just purchased a smoke machine to do exactly what you have done. I'm not looking at judging but i have another post on my car idling too high which, as Duke said, could be a Vac leak or the refurbished carbs themselves.

I too would love to see a guide on which hoses to connect the smoke machine too to check each circuit. Its a bit daunting under the bonnet of one of these big block cars with A/C and PS but i'm sure there's a process to follow to check all the hose connections and relay valves. I'll know more after this weekend i suspect.

I also see comments and instructions from Mark E above that are very welcome as I've purchased smoke solution that doesn't leave residue.

Cheers
Grahame

[Richard R.]

Hi Grahame,
All I could suggest is to start one circuit at a time. Headlights, wiper, vacuum tank, etc. along with the suggestions made on this thread. In dealing with the idle, I would first eliminate/disconnect all systems not related to engine operation. If you still think it is a vac leak with the carbs/intake I would take a propane torch and open it up without lighting and run the torch around the intake and carbs while the engine is running to see if the rpm's change. That might help locate the problem.

Best of luck!

[Grahame M.]

Thanks Richard, I have all the tools for this weekend including a propane torch. Thanks for your help.

Cheers
Grahame