Quote:
Originally Posted by fletchusmc
Haven't voted yet and not sure if I should add this to this thread but, what's the difference in the way the vacuum pump should run with key on engine off or key on engine on? The reason I ask is I just went out this morning, turned the key on engine cold. Pump runs and doesn't stop. Started the engine and let it run for close to 10 minutes and the pump never came on (but does come on when I disconnect the vacuum line). Turned off the engine and immediately turned the key back on and now the pump is on off on off on off constantly.
Drives great all the way up to the limiter. Just wondering what the difference in engine on and engine off when it comes to the vacuum.
1995, #297. Stock except Corsas.
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You will see Vacuum Check Valve #15 in Paul's post (this diagram is for a 1990 ZR-1) which lets Plenum Vacuum take over when engine is idling and Plenum Vacuum is high. Vacuum pump takes over when engine has wide open throttle and Plenum Vacuum is lower.
Cruise Control and HVAC on passenger side of Plenum and Secondary Vacuum on Drivers side of Plenum.
Secondary Vacuum System for a 1990 ZR-1.
1. In your case you had High Plenum Vacuum at idle for 10 minutes (so vacuum pump remained off).
2. Pump came on when you disconnected vacuum line cutting off Plenum Vacuum to the pump.
3. With Key on and No Plenum Vacuum, Pump will cycle maintaining Secondary Vacuum as it is suppose to do. The more often the vacuum pump cycles the indication of more vacuum leaks present.
4. Pump cycling on and off every minute indicates minimal Vacuum Leaks under the Plenum. Pump cycling on and off every 5 seconds indicates Vacuum Leaks under the Plenum (Secondaries will remain operational as pump can keep up with the leaks if it cycles off no matter the cycle time).
When you first turned the key on and Vacuum Pump ran constantly......that might indicate the check valve #15 was stuck open or leaking and the pump could not build up vacuum because it was sucking air from the plenum.
Or....that might indicate with engine cold the vacuum leaks are unacceptable and with engine warmed up the Vacuum Leaks under the Plenum are significantly less (vacuum lines/connectors swell up closing down some vacuum leaks).