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84'Eldorado cruise control


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confirmed, no vacuum with car running in drive at brake servo.

next?

Time to trace the line and look for a large leak or a point where it is disconnected.

From what I see the hose on the inside of the cabin goes to a grommet and the outside of that is a bigger diameter hose that goes into a 3 side tee connector which the second connection goes to a small hose plugged with a screw. This obviously had to go to the cruise control servo ( which is NOT in the car) the last tee connects a hose going to a metal tube right near the vacuum pump, runs around the front of the motor and goes into the bottom of the carburetor.

I would think that the vacuum origin is from the carburetor so if I removed the end of the hose coming out of the carb right before it goes into the metal tube should I feel vacuum there regardless if car is in drive or not?

No carburetor on a HT-4100. It has throttle body fuel injection. That would be the source of vacuum.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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The source of the vacuum is a combination of the throttle body and the vacuum pump. In the diagram linked in post #16 above, the first tee you see outside the firewall is the tee in the diagram and the hose going through the firewall as the "body feed."

The purpose of the vacuum pump is to provide vacuum when the engine vacuum is low, as when the vehicle is accelerating or climbing grades. It keeps the windshield wipers going and keeps everything else that is vacuum-driven working continuously.

The diagram may be generic as opposed to specifically for your car, or be for a different car, but it probably is applicable to your car in that we have a prime source at the throttle body with the vacuum pump being the source of vacuum supplied to the car.

The vacuum pump boosts vacuum when it is below a certain amount, say 12 inches Hg, to provide a regulated source of vacuum for the car. The prime source is the throttle body. When the throttle body provides zero vacuum, such as at full throttle at low speed or the engine stalls, the vacuum pump can pump air into the engine compartment through the "filter" on the component in the diagram between the throttle body and the vacuum pump.

So the best place to measure vacuum is at the hose from the vacuum pump to power brake booster servo, or at the big tee right out of the firewall.

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