HT4100 4.1, 4.5, 4.9 Discussion, In search of a new/rebuilt vacuum pump... in Cadillac Engine Technical Discussion; I know what you are talking about. If this thing has a leak, I'm guessing the entire system can't hold ...
I know what you are talking about. If this thing has a leak, I'm guessing the entire system can't hold a vacuum? Something to look at I guess. My Caddy is sitting down at a garage right now and they are trying to figure out why it won't start on occasion when it is hot.
BTW I spent some time with a vacuum gauge taking readings today. With the engine off, the factory vacuum pump puts out a constant 15 hg of vacuum. When the vacuum pump disabled (fuse pulled) the engine alone also puts out 15 hg of vacuum. When the vacuum pump is running and the engine is idling, the vacuum load is approx 22 hg of vacuum.
When driving, there is 15-25 hg of vacuum with the pump enabled and 5-25 hg when the pump is disabled (the low numbers come up when the engine is under acceleration load, while the high numbers are from deceleration). Based on this I would say that the pump is necessary to maintain a suitable vacuum floor of 15 hg.
The only thing I noticed was that brakes were weaker with the pump disengaged. Cruise control and A/C still worked, although I think all of the cabin controls are on a separate vacuum harness (under the steering column according to one of the books).
Builds 24" of vacuum.
Dimensions: 8" L x 5" W x 7" H (approximate).
Draws 10 amps.
Flow rate: 1.53 cfm.
Includes 12 volt vacuum pump, switching relay, vacuum line and control, mounting insulators and hardware.
Turns on at 18" and shuts off at 23" of vacuum.
24 hg is more than these old cars usually have. However it's nice that it has an integrated vacuum switch.
Supposedly some of the early-80s Chevy Celebrity and other J-series cars have a pump with an integrated switch. I don't know if ours are supposed to have a switch or not, but I do know that mine's not working if it's supposed to have one.