Headlights open with engine running.
Thread Starter
Race Director
Joined: Jan 2002
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From: No Where USA
Headlights open with engine running.
My headlights open when engine is running. That tells me there's a vacuum leak. Well I took out my vacuum pump and hooked it up at the spot where it gets the vacuum when the engine is running and everything works.
Team Owner
Joined: Jan 2006
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From: Crossville TN
Bad connection on a vacuum hose or a split in it, or a rub-thru. Possibly leakage in a related vacuum component. If you can find a diagram of the vacuum system for your car and you have some understanding of which lines have vacuum on them when different parts of the system are being operated, you can identify the possible candidates for vacuum leakage OR improper supply of vacuum (where it should NOT be present) can result in your symptoms.
P.S. I've never had much luck with using a Miti-Vac to diagnose a C3's vacuum system. Maybe it would work for checking integrity (or leakage) in a specific line or component. A running engine supplies ample vacuum to actuate all the stuff in that system, and a vacuum gauge can tell you whether vacuum level is being maintained...or not.
P.S. I've never had much luck with using a Miti-Vac to diagnose a C3's vacuum system. Maybe it would work for checking integrity (or leakage) in a specific line or component. A running engine supplies ample vacuum to actuate all the stuff in that system, and a vacuum gauge can tell you whether vacuum level is being maintained...or not.
Old Fart Pilot
Joined: Apr 2010
Posts: 1,891
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From: Spokane, WA
When you say everything works (correctly) using your vacuum pump connected to "where it gets the vacuum when the engine is running" did you disconnect the normal system hose right at the intake manifold fitting, at the filter, the 1 tp 2 check valve, or the vacuum tank?
Where you actually applied vacuum to get it successfully operating will help greatly trying to determine where your problem(s) are.
Where you actually applied vacuum to get it successfully operating will help greatly trying to determine where your problem(s) are.
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From: Sunshine Coast, Queensland, Australia
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OK. You have a large vacuum line and a small vacuum line going up to the front of the car.
The large line is the vacuum that actually opens and closes the headlight doors. Under the circumstances, its pretty safe to say that side of the system is working.
OK, That small line. It's connected to the top of the headlight relays, it's the switching line so to speak. When it has vacuum it pulls the dogbones in the relays up. Causing the vacuum to be diverted to the close the doors side of the actuators. When zero vacuum is present to the top of the relays. A spring in them pushes the dog bones down, diverting vacuum to the open the doors side of the actuators.
So, in a nut shell. When your engine is running. You have plenty of vacuum to the main or large vacuum line to the front of the car. But no vacuum coming through the small line.
Start at the tee behind the vacuum filter in the engine compartment. Is it connected? Move under the dash to the over ride switch. Is it connected? Unhook the line. Is it getting vacuum? Then through the over ride switch to the headlight switch, are both lines connected? Etc. All the way out to the front of the car.
The large line is the vacuum that actually opens and closes the headlight doors. Under the circumstances, its pretty safe to say that side of the system is working.
OK, That small line. It's connected to the top of the headlight relays, it's the switching line so to speak. When it has vacuum it pulls the dogbones in the relays up. Causing the vacuum to be diverted to the close the doors side of the actuators. When zero vacuum is present to the top of the relays. A spring in them pushes the dog bones down, diverting vacuum to the open the doors side of the actuators.
So, in a nut shell. When your engine is running. You have plenty of vacuum to the main or large vacuum line to the front of the car. But no vacuum coming through the small line.
Start at the tee behind the vacuum filter in the engine compartment. Is it connected? Move under the dash to the over ride switch. Is it connected? Unhook the line. Is it getting vacuum? Then through the over ride switch to the headlight switch, are both lines connected? Etc. All the way out to the front of the car.
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Joined: Mar 2020
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From: US-PNW
P.S. I've never had much luck with using a Miti-Vac to diagnose a C3's vacuum system. Maybe it would work for checking integrity (or leakage) in a specific line or component. A running engine supplies ample vacuum to actuate all the stuff in that system, and a vacuum gauge can tell you whether vacuum level is being maintained...or not.
You got that right! A mity-vac has such small volume I'd bet the normal leakage in a working system would easily make up and keep up with the volume taken by the mity-vac. I tested the large vacuum cans for my headlights and to draw enough air out to test them needed something like 100+ strokes each. My forearms were aching! Let's hope 540 has an electric vacuum pump!
Thread Starter
Race Director
Joined: Jan 2002
Posts: 11,614
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From: No Where USA
When you say everything works (correctly) using your vacuum pump connected to "where it gets the vacuum when the engine is running" did you disconnect the normal system hose right at the intake manifold fitting, at the filter, the 1 tp 2 check valve, or the vacuum tank?
Where you actually applied vacuum to get it successfully operating will help greatly trying to determine where your problem(s) are.
Where you actually applied vacuum to get it successfully operating will help greatly trying to determine where your problem(s) are.
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Thread Starter
Race Director
Joined: Jan 2002
Posts: 11,614
Likes: 347
From: No Where USA
You got that right! A mity-vac has such small volume I'd bet the normal leakage in a working system would easily make up and keep up with the volume taken by the mity-vac. I tested the large vacuum cans for my headlights and to draw enough air out to test them needed something like 100+ strokes each. My forearms were aching! Let's hope 540 has an electric vacuum pump!
Old Fart Pilot
Joined: Apr 2010
Posts: 1,891
Likes: 959
From: Spokane, WA
Could you possible have connected yours to a ported vacuum source on the carb?