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91 Deville 4.9


stixboy

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hi guys, me again. once again i thank everyone who helped me with my past problems. here's another for ya.

i've had my car for five years now and i've noticed i never hear my level control pump running. the only time i hear the pump is after i start my car. every time, no matter what, after i start my car i hear the level control pump run for about 4-5 seconds and then it goes off. now my friend has the exact same car and i hear his pump running when the car isn't even on, and i know my car should be doing that. i even hear some pumps running on a couple of lincolns around town. my car does seem to sit a little low in the rear end, and always has ever since i got it. but i don't know if this is because of my suspension level control system problem. i know if there's someone in my back seat it sits very low, so do i have shot shocks also?

so my two questions are:

1- is my suspension level control system working properly, if not how can i fix it

2- are my shocks or struts or whatever shot? shocks, struts, springs? what's the difference and how can i fix this?

PLEASE PLEASE HELP!!!!!!!

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Info on the system from my 92 shop manual:

In order to ensure that the Electronic Level Control system is operating with at least minimum air pressure, the height sensor commands an air replenishment cycle each time the ignition is cycled on. [so each time you start your car you hear the motor run.]

The air replenishment cycle works as follows:

Height sensor position is checked when the ignition is turned on. If the height sensor indicates that it is not necessary to raise or lower the car, an internal timer circuit is activated. After a delay of 35-45 seconds, the compressor is turned on for 3-5 seconds. This ensures that the air adjustable struts are filled with adequate residual pressure.

If weight is added or removed from the car during the 40 sec delay, the air replenishment cycle will be overridden and the car will raise or lower after the normal 13-27 sec delay.

Raising car

When a load is added to the vehicle, the vehicle body is forced downward causing the height sensor actuating arm to rotate upward. The upward rotation of the height sensor arm activates the internal timing circuit. After an initial time delay of 13-27 sec, the sensor grounds pin 3 which completes the compressor relay circuit to ground. With the relay energized, the 12V+ circuit to the compressor is complete and the compressor runs, sending pressurized air to the air adjustable struts through the plastic tubing.

As the air adjustable struts inflate, the vehicle body moves upward, rotating hte height sensor actuating arm back toward its original position prioro to the load addition. Once the body reaches its original height +- 1 inch the sensor opens the compressor relay circuit and shuts off the compressor.

Similar for lowering.

Bruce

2016 Cadillac ATS-V gray/black

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so now i guess i know it does work properly and doesn't have a leak. because if i had a leak the compressor would continually run right? and it's not doing that so thank god for that.

and it doesn't turn on anymore after the first cycle every time i start the car. no matter if i add weight to the vehicle or not. and besides the compressor, it does seem to sag a little in the back, so what should i replace in my rear end.

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The factory test is you add a 300 lb weight to the rear of the car, which should cause the rear to go down, and observe that after the programmed delay the rear pumps back up.

The key to system operation is the position of the level determining lever, so the first step is get under the back of the vehicle and identify the compressor, and then the height sensor actuating arm. I recall a report that their height sensor actuating arm had gotten bent, causing a change in system operation.

Bruce

2016 Cadillac ATS-V gray/black

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The leveling compressor should start in a few seconds after you turn ignition ON (even when engine is not running). Because your car is old, even if you did not put anything in the trunk, the compressor will run for a few seconds to bring the rear of the car to some reference point to compensate for the air pressure leaked say over night. My impression is that your reference point is out of range. Do not really know much about it, just a suggestion. If you cannot find the culprit, I would just replace the rear struts with permanent ones (not automatically inflatable).

As for leaks, an easy place to check out is the fitting right on the shock. If you jack up the rear of the car, you'll see it. You do not even need to remove the tire. Spray soap water and watch/listen.

The saddest thing in life is wasted talent

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so now i guess i know it does work properly and doesn't have a leak. because if i had a leak the compressor would continually run right? and it's not doing that so thank god for that.

and it doesn't turn on anymore after the first cycle every time i start the car. no matter if i add weight to the vehicle or not. and besides the compressor, it does seem to sag a little in the back, so what should i replace in my rear end.

The compressor would run continually only if you had a massive leak. It is not the case as I see. You do have some leak, but it might be acceptable. The system somehow lost the correct reference point, that's what I think.

The saddest thing in life is wasted talent

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i've had the rear end jacked up plenty of times and never noticed any air escaping. plus this has been going on for five years so i'm going to go with adjusting the actuator arm. so how do i go about doing this. and if i've lost a "reference point" can it be reset somehow?

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I think this is the relevant text:

Height Sensor Adjustment

The attaching link should be securely connected to the sensor actuating arm when any adjustments are made.

1. loosen the lock nut that secures teh metal sensor arm to the plastic sensor arm bracket.

2. to raise the vehicle trim height (i.e., turn the compressor ON with less travel fo the rear suspension), move te plastic arm up toward the top of the slot and retighten the lock nut.

3. to lower the vehicle trim height (i.e., turn the comrpessor ON only after aditional travel of the rear suspension) move the plastic arm to the bottom of the slot and retighten the lock nut.

The picture appears to show the sensor as a small box with a flange attached, with 2 mounting screws, and a wire coming out of it.

The box has a lever coming out of it, and connecting to a small height sensor link.

Bruce

2016 Cadillac ATS-V gray/black

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Some photos would be great, as we do get this question now and then and my current Cadillac CTS doesn't have ELC.

Bruce

2016 Cadillac ATS-V gray/black

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Are you sure the noise you hear when starting your car is the ELC compressor or the fuel pump? If you turn the ignition to the ON position and sit on the rear bumper, the ELC system should level the car out. If the compressor runs but the car doesn't level out, there is a leak in the system. Check the rear shocks, the tubing from the compressor to the shocks or the compressor head itself.

You can also disconnect the level sensor arm from the frame and move the arm to simulate a load in the trunk and the system should activate.

Most of the failures in the ELC systems are chafed tubing where it passes by suspension arms, etc. The dealer parts counter sells a splice kit if that is what you find a leak.

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

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