Mechanics

SUSPENSION CONTROL

1998 Cadillac Deville

Suspension problem
1998 Cadillac Deville V8 Front Wheel Drive Automatic 85000 miles

I have a 1998 Deville. The vehicle bottoms out frequently, more so as passengers are added. I'm not convinced it't the shocks (which are extremely expensive to repair). I've checked the fuses and they seem OK. What else can it be other than shocks? I know the Devilles have some type of controllable air shocks. Thanks in advance.
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Jon8331
January 27, 2009.




Hello ..thanks for the donation .. much appreciated

All models are equipped with the ELC ..you would have to check whether your model has CVRSS...I have enclosed a description and a couple of test's to carry out .. hope this helps .. let me know

DESCRIPTION
NOTE:This article covers models equipped with Electronic Level Control (ELC) as a stand-alone system. For information on models that are equipped with both ELC and Continuously Variable Road-Sensing Suspension (CVRSS), see ELECTRONIC - LEVEL CONTROL - CADILLAC WITH CVRSS article.

Electronic Level Control (ELC) system automatically raises or lowers rear of vehicle to correct ride height (curb height), compensating for load added to or removed from vehicle. System consists of a compressor, air drier, exhaust solenoid, ELC relay, height sensor, air adjustable struts, pressure limiter and connecting air lines.
SYSTEM OPERATION
When ride height decreases due to weight being added to vehicle, height sensor arm assembly rotates upward in relation to height sensor. See Fig. 1 . This activates a timing circuit in height sensor. After a delay of about 13-27 seconds, height sensor grounds ELC relay, turning on compressor. Air is then pumped into struts, raising vehicle. Delay prevents system from operating during normal changes in ride height that occur during driving. As vehicle rises, height sensor rotates downward. When vehicle rises to within one inch (25.4 mm) of curb height, height sensor opens ground circuit to ELC relay, turning compressor off.
When ride height increases due to weight being removed from vehicle, height sensor arm assembly rotates downward. This activates the timing circuit in height sensor. After a delay of about 13-27 seconds, height sensor grounds exhaust solenoid valve circuit, causing air to be vented from struts, lowering vehicle. When vehicle has lowered to within one inch (25.4 mm) of curb height, height sensor opens exhaust solenoid valve circuit, causing exhaust solenoid valve to close.
To ensure system is operating with at least minimum air pressure, height sensor commands an air replenishment cycle each time ignition is turned on. An internal timer circuit is activated when ignition is turned on. After a delay of about 35-45 seconds, compressor turns on for 3-5 seconds to ensure residual system pressure exists. If weight is added to or removed from vehicle during 35-45 second delay, air replenishment cycle will be overridden and vehicle will rise or lower after normal time delay.
Voltage is applied to compressor, ELC relay, inflator timer and height sensor at all times. This allows system to vent if load is removed with ignition off. Height sensor limits compressor operation or exhaust solenoid energized time to 7 minutes. Time limit is necessary to prevent continuous compressor operation in case of air leak. Turning ignition switch from OFF to ON position resets compressor operation or exhaust solenoid valve energized time.
COMPONENT OPERATION
Air Adjustable Struts
Air adjustable strut is a conventional strut enclosed in an air chamber, which extends when air pressure is increased in chamber.
Air Drier
Air drier, attached to compressor output, absorbs moisture from air being delivered to air adjustable struts. Air drier contains a valve that maintains a minimum air pressure of 7-14 psi (.49-.98 kg/cm2 ) in struts.
Compressor
Compressor, located on right rear suspension support, provides air pressure for system operation. Compressor head casting contains intake and exhaust valves, and exhaust solenoid valve.
ELC Relay
ELC relay is located in trunk, below center of rear shelf. When ELC relay is grounded by height sensor, voltage is supplied to compressor.
Exhaust Solenoid Valve
Exhaust solenoid valve, located in compressor head assembly, exhausts air from the system and limits compressor output pressure.
Height Sensor
Height sensor, mounted to rear underbody frame, links body to left rear suspension arm. Sensor controls ground circuits of ELC relay and exhaust solenoid valve.
ADJUSTMENTS
HEIGHT SENSOR
Park vehicle on level surface. Ensure fuel tank is full and vehicle is unloaded. If necessary, simulate full tank by adding appropriate amount of weight to vehicle (about 7 lbs. for every gallon less than full). Ensure tire inflation pressure is correct. Move front seat rearward. Turn ignition on to activate ELC system. Bounce rear of vehicle 3 times to normalize suspension.
Measure rear ride height. See REAR RIDE HEIGHT . If rear ride height varies by more than 1/2" (12 mm) from side to side, or is lower than specified, repair suspension problem before continuing procedure. If ride height is as specified, height sensor is adjusted.
NOTE:Height sensor arm assembly can be moved a total of 5 degrees. One degree of change at height sensor arm assembly results in a 1/4" (6 mm) change in height at rear bumper.

If rear ride height is not within specification, loosen lock bolt on sensor arm. See Fig. 1 . To increase ride height, move plastic arm upward. To decrease ride height, move plastic arm downward. Tighten lock nut.
Fig. 1: Adjusting Height Sensor


http://www.2carpros.com/forum/automotive_pictures/266999_cad_1.jpg


REAR RIDE HEIGHT
Mark a spot on bottom of rocker panel, 22 3/16" (563 mm) forward of rear axle center line (distance "A"). See Fig. 2 . Measure distance between marked spot and ground (distance "B"). If vehicle is on hoist, consider ground line to be horizontal line between bottom of front and rear tires. Distance "B" should be 7 9/16 - 8 11/32" (192-212 mm).


http://www.2carpros.com/forum/automotive_pictures/266999_cad1_1.jpg



DESCRIPTION
NOTE:Models are also equipped with Continuously Variable Road-Sensing Suspension (CVRSS). For information on CVRSS, see ELECTRONIC - CV ROAD-SENSING - CADILLAC article.

Electronic Level Control (ELC) system automatically raises or lowers rear of vehicle to correct riding height (curb height), compensating for load added to or removed from vehicle. System consists of an air compressor, air drier, exhaust solenoid valve, compressor relay, 2 position sensors, air adjustable rear shock absorbers, Road-Sensing Suspension (RSS) control module, and connecting air lines. ELC air compressor is controlled by RSS control module.

NOTE:All models are also equipped with Electronic Level Control (ELC). For information on ELC system, see ELECTRONIC - LEVEL CONTROL - CADILLAC WITH CVRSS article.

Continuously Variable Road-Sensing Suspension (CVRSS) system performs 2 functions:
Controls firmness of vehicle ride (this part of the system is called CVRSS, although the term CVRSS is also applied to the entire system.
Adjusts vehicle riding height (this part of the system is called Electronic Level Control, or ELC).
CVRSS control module monitors system for faults. If a fault occurs, codes are stored in memory. See SELF-DIAGNOSTICS under DIAGNOSIS & TESTING. Self-diagnostics also allows technician to monitor CVRSS system data, inputs and outputs.
CONTINUOUSLY VARIABLE ROAD-SENSING SUSPENSION (CVRSS)
Continuously Variable Road-Sensing Suspension (CVRSS) system can change firmness of vehicle ride in 10 milliseconds. Vehicle ride firmness is determined by how easily the strut or shock absorber can be compressed (damping characteristics). In each strut and shock absorber, damper oil flows through a damper that has 2 different sized orifices, one for firm mode and the other for soft mode. A damper actuator rotates the damper between positions (modes). Damper actuator is an integral part of strut and is not serviceable separately from strut. Damper actuators respond to command signals from CVRSS control module. CVRSS control module command signals are based on the following inputs.
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Dave H
Jan 29, 2009.
Great information - thanks

But I'm not a great mechanic. It would be helpful if you could tell me what you think the problem is or what to check in order to diagnose the problem. I don't think it's the shocks. What would you do to figure it out.

Thanks

Tiny
Jon8331
Jan 29, 2009.
Hello

I cannot possibly give an opinion of where the fault actually lies. We could start changeing part's without reason costing $$ along the way? You will need to carry out the following test's if you think the actual shocks are not the fault ! Start these test's they are quite simple and let me know when you need another test to perform. !

SYSTEM OPERATION TEST
NOTE: Ensure height sensor arm assembly and link assembly are in good condition before performing system operation test.

Open hood and trunk. Turn ignition off. Place vehicle on flat surface. Measure distance from ground to top of rear wheelwell opening. This distance is unloaded height. Start engine. Cycle ignition off then on to reset system. Add 300 lbs. (136 kg) of weight to trunk. Allow at least 28 seconds for delay. If compressor starts, go to step 4.
If compressor does not start and vehicle is within one inch (25.4 mm) of unloaded height, perform SYSTEM DOES NOT EXHAUST test under SYMPTOM TESTS.
If compressor does not start and vehicle is not within one inch (25.4 mm) of unloaded height, perform HEIGHT SENSOR adjustment under ADJUSTMENTS, and then retest system. If compressor still does not operate after adjusting height sensor, perform COMPRESSOR DOES NOT OPERATE test under SYMPTOM TESTS.
If compressor stops within 7 minutes, go to next step. If compressor runs continuously, check for the following conditions. If none of the following conditions exists, replace height sensor: Stuck ELC relay.
Short to ground in Yellow wire between ELC relay and height sensor.
Short to voltage in Dark Green wire between ELC relay and compressor connector.
If system leaks down, perform IMPROPER OR CONTINUOUS EXHAUST test under SYMPTOM TESTS. If vehicle returns to within one inch (25.4 mm) of unloaded height, remove load and go to next step. If vehicle does not return to within one inch (25.4 mm) of unloaded height, perform HEIGHT SENSOR adjustment under ADJUSTMENTS, and then retest system. If compressor still does not stop within 7 minutes, perform IMPROPER OR CONTINUOUS EXHAUST test under SYMPTOM TESTS.
If system exhausts within 28 seconds, go to next step. If system does not exhaust within 28 seconds, perform SYSTEM DOES NOT EXHAUST test under SYMPTOM TESTS.
If vehicle returns to within one inch (25.4 mm) of unloaded height after 2 minutes of exhaust, system is operating correctly. If vehicle does not return to within one inch (25.4 mm) of unloaded height after 2 minutes of exhaust, adjust height sensor. See HEIGHT SENSOR under ADJUSTMENTS.

Dave H
Jan 29, 2009.
Hi I have this same system, ELC, on my 85 Buick Riviera. The operation as you described is exactly the same. I am having problems with the compressors leaking down over a period of time one to two hours. I have found many places on the internet that rebuild these for other GM and Ford models. However they don't rebuild the 79-85 systems, just the 95-99 and various other GM's from 86-current. After discussing with the Supervisor that the air dryer in these compressors for the Riv had a valving arrangement just for E-bodies that needed to maintain 15-20 psi at all times they agreed to rebuild it since, " they were all the same pretty much" according to the company. The valving arrangement is just a couple of springs and a rubber flap like a check valve that is inside the dryer on the system. I've also built myself an ELC tester very similar to the ones the service manual says to use. Now I've found that the rebuilt compressor is leaking down after about two hours. There were a few hicups during this rebuild process with the company Rep finally saying they were not going to rebuild these anymore for the 79-85 models!

Does anyone have any suggestions on how to get these compressors rebuilt where they don't leak down? I'm suprised more people aren't having trouble with these.

Is there any other company out there that maybe I don't know about that would consider rebuilding these? Since our 79-85's are getting some collector attention I'm sure the need for these will be more in demand, not to mention it's the same compressors used for Eldo and Toro of this vintage.

Sorry but manually adding air to the system is not something I'm interested in doing either. Thanks

Tiny
Sosuzguy
Oct 25, 2009.

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