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Electronic Leveling Control (ELC) - How often should it activate?


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Hello All,

Sorry I have been popping up here more to ask questions than to answer any. Life's been throwing a lot of busy-ness my way lately.

A couple of months ago I installed a new set of front struts along with Gabriel rear shocks with the air leveling feature. The ELC seems to be working perfectly with one possible exception: it may be having to run "too often," but I'm not certain what "too often" is, exactly.

If the car sits overnight I will definitely have some "sag" at the rear and will immediately get a Car Is Leveling light, sometimes before I start the car if I'm slow about doing that after I get in. It will also do the same thing, but the time to level is shorter, after sitting for several hours. I only occasionally get the Car Is Leveling light while driving, and this tends to be after cornering fairly hard or heading up a steep grade.

Once the shocks have been pumped up, how long should that air be held before it needs to run a leveling cycle again? I am presuming, of course, that we're talking about this without there having been a change in the load in either the rear seat or trunk. I know that if you add (or subtract) several rear-seat passengers or a load of stuff in the trunk the car will level.

When I checked the system after getting everything installed again there is clearly a slow, very slow, leak where the air line that leads back to the shocks connects to the overpressure valve. There may, possibly, be others at the various fittings and I need to check again. I don't believe there could be a major leak in the air lines anywhere or else the car would not be able to level nor stay level at all.

Since I'd like to have everything working as designed I'm turning to those who've "been there, done that" to find out what constitutes within normal limits for ELC retention of pressure, frequency of activation of the compressor, and length of activation of the compressor.

Thanks for your insights.

Brian

Brian

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Bri the Tech Guy   http://britechguy.com
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My Fleetwood levels out every time I start the engine or if I turn the ignition to ON. Sometimes it's only for a second. If I let it sit overnight, the LEVEL RIDE light will come on for 2-3 seconds. It has done that since it was new. My Deville and Seville will activate the ELC system in the same way but since there is no light on the dash, the only way I know it is to lower the window and listen for the compressor. Those cars do not have the light on the dash so there is no way of knowing when the system is operating. I think deleting that light was not a good idea but I digress....

If your light is coming on while driving, that usually indicates there is a leak in the system.

Use a spray bottle with water and some dish soap to spray the lines, fittings, compressor body, etc. and you'll find the leak(s).

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

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Thanks to all who took the time to reply.

The Owner's Manual states that the system is supposed to release a bit of air and then pump the shocks up to minimum pressure again when the car is started, but I wasn't sure whether or not that would/should activate the light or not.

I almost certainly have a slow leak or leaks, so next on the "to do" list will be checking each and every connection for leaking. The O-rings have probably begun to perish after this many years.

Brian

Brian

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Bri the Tech Guy   http://britechguy.com
britechguy@gmail.com   (540) 324-5032
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Check the entire length of the air lines for leaks from the compressor to the rear shocks. Sometimes, the lines will wear through on suspension components and leak where there is not a connection.

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

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Mine all kick on on key cycle,

My Deville would always drop a little over a week, but never sat still long enough, The shocks were seeping.

Cant tell if it comes on while driving because none of mine have the indicator

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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  • 2 months later...

Ladies & Gentlemen,

I'm back with the next question on the ELC and possible failures. First, a bit of background. I have checked all of the connections coming out of the compressor (though you can see the one to the input side of the pressure limiter valve has a leak in this video after I moved the valve) and the pressure limiter valve and they all were not leaking. For several weeks I had what seemed to be textbook ELC behavior: Would activate when the car was started to do its "exhaust slightly then pump things back up to minimum pressure" routine which took less than 10 seconds most of the time.

Within the last few days I'm suddenly having activation of the compressor once every few minutes any time I'm driving so that indicated something was clearly wrong. Today I decided to re-check those connections near the compressor and all were perfectly tight (until I moved the pressure limiter valve) but there were pronounced bubbles emanating from the side of the pressure limiter valve that faces the compressor when it's hooked on to its mount. I took it off so that I could see what was happening on that side. Since a video is worth a thousand words (and is only 30 seconds long), here's what I found: Presumed Pressure Limiter Valve "Gusher" Leak. As you can see, when the compressor is running air is just streaming out of the two small holes on the side of this valve at a rate that just blows the soapy water away before it can even land. After the compressor is off it's still doing this, but not with quite so much force, so the only source of pressure at that point would be coming in to the valve from the "shock side" of the system. I fail to believe this is normal since the documentation notes, The limiter valve restricts maximum pressure to the rear struts to 447-510 kPa (64-74 PSI). There is nowhere near to that pressure in the system, as the car is no longer raising itself anymore (or at least not to the naked eye). I guess there could be an obstruction in the main feed tube to the struts, but that seems to me to be unlikely.

Do these pressure limiter valves have a history of failing? If not, is there a specific area of the system downstream of the compressor that warrants looking at first?

Brian

Brian

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I don't think I've heard of one failing but that doesn't mean they don't fail. It looks like you've found the issue with the level control system. I wouldn't think it should leak from the body of the device when the compressor is running but it should not leak at the tubing connection when the compressor is off.

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

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Thanks Kevin. The main reason I ask is it looks like this item would be a "junkyard scavenged part" if I actually need to get one. I haven't had a lot of luck (and that's no surprise) finding one of these as a new part. I was just wondering if this was a characteristic problem or not.

It's really annoying to have had everything working correctly and then for this to happen so shortly afterward.

Brian

Brian

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Bri the Tech Guy   http://britechguy.com
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  • 2 weeks later...

Back with a follow-up. I'm still on the search for a replacement pressure limiter valve since it's clear that anything that's "going in" to the system is "going out" through the small air escape holes on the side of the valve. I think it's become "stuck open" for some reason.

In addition, today I managed to snap the line that exits that valve and takes the air back to the shocks when I was trying to determine where it actually exits the engine bay to make it's way toward the back. So, it's off to the auto parts store tomorrow for a Monroe AK29 air line kit. It certainly won't hurt to replace these lines anyway.

What I'm wondering is whether anyone has ever deleted the pressure limiter valve? It seems to me that the probability of this device ever serving its intended purpose is quite remote as long as the height sensor works. I'd think the only way it could ever come into play is if the height sensor failed in such a way that it created a "constant on" condition for the compressor.

I would at least reconnect the system without the pressure limiter valve while I search for one unless there's a good (as in likely damage failure, not remotely possible but very improbable) reason I should not. What says the cohort?

Brian

Brian

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I think what you're calling the pressure limiter valve is actially the exhaust solenoid. It will be energized in order to reduce head pressure when the ignition is turned on. Once the compressor starts to run, the exhaust solenoid is de-energized and the system builds pressure. It has a dual function - to exhaust air from the rear shocks to lower the car and to act as a pressure relief valve to limit the maximum air pressure from the compressor. According to the shop manual, it is a non-serviceable part but you may be able to replace it with one from a junkyard. That information was from a 1996 shop manual but the level control systems were basically the same all the way back to the 1970's.

I'd be inclined to replace the entire compressor assembly with one from a lower mileage car from the junkyard.

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

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No, the pressure limiter valve is not the exhaust solenoid but is placed inline between the compressor output and the main line back to the shocks. There's a very short air line that comes out of the air dryer (dessicator) and runs to the pressure limiter valve. The main air line to the rear is attached to the opposite end of the valve. The ends of the valve have slightly different sizes as do the fittings that attach to it. It's discussed and shown in the figures in the Service Information Manual. It couldn't be more clear in the video I posted above.

The compressor works like a charm and, from all other evidence, so does the solenoid valve.

Brian

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Bri the Tech Guy   http://britechguy.com
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Thats weird. I dont think any of mine have anything inline.

The exhaust valve is mainly used when a load is removed from the vehicle and the weight is reduced, therefore not needing as much air in the airbags.

Could you possibly post a picture of the valve you speak of. I would like to learn a little bit

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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No, the pressure limiter valve is not the exhaust solenoid but is placed inline between the compressor output and the main line back to the shocks. There's a very short air line that comes out of the air dryer (dessicator) and runs to the pressure limiter valve. The main air line to the rear is attached to the opposite end of the valve. The ends of the valve have slightly different sizes as do the fittings that attach to it. It's discussed and shown in the figures in the Service Information Manual. It couldn't be more clear in the video I posted above.

The compressor works like a charm and, from all other evidence, so does the solenoid valve.

I watched the video again - and see that it must be a separate part. There is also no wires going to the unit so it must be some sort of mechanical device. It looks like it would be a servicable part but these days, one never knows - it may have long since been discontinued. Those things must be a dime-a-dozen at the junkyard. I'd be inclined to buy the whole compressor assembly for spare parts.

The compressor assembly used to have three servicable components - the head assembly, the motor and the exhaust solenoid. I rebuilt one years ago on a 1985 Fleetwood Brougham d'Elegance. None of the parts were bad but the compressor head just needed to be resealed.

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

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Here's the diagram from the Service Information Manual:

ELC_Compressor_Assy%26HeightSensor.jpg

Sorry for the fuzziness, but this is at the bound edge of the page making it difficult to scan cleanly. You can see the pressure limiter valve shown as #5. The clip (#7) is, for all practical intents and purposes part of it since it's pressed on and any attempt to remove it would most likely bend it such that it wouldn't hold again.

Every car I've seen from 1989-1993 has this as part of the system and they're always clipped on to the compressor mount and located right next to it. The fact that they're brass make's them quite visible, even once tarnished.

Most of my used parts came from a "you pull 'em" salvage yard (now, sadly, they've discontinued the "you pull 'em" option as of a couple weeks ago since many pullers were damaging many other parts to get to what they wanted) and all the cars I've pulled from were 1990 to 1992 model years. If these things actually disappeared from the ELC later, and the compressor setup is pretty much the same, I suspect they were found to be unnecessary. The yard I was having scavenge for this part says they've come up with it, but I have to go over and check. It was so much easier to pull this sort of thing myself.

Brian

Brian

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Bri the Tech Guy   http://britechguy.com
britechguy@gmail.com   (540) 324-5032
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thank you.

Definately dont recall it being in anything newer.

Compressor looks the same though.

The compressors were pretty much identical among GMs for a long time.

Only things that are different is the mounting bracket that the compressor bolts to,

and the dryer where the shock hose(s) go to.

Some are single output, some are dual.

I have pulled comressors off buicks (like the riviera) and olds (aurora) and put them right on.

I actually put a 2001 catera compressor in my 96 Deville a few years back, only difference was the catera had single output, my deville had dual. Swapped dryer and it was perfect. None of these that I have mentioned have I recalled that valve.

I am thinking they likely deleted it after 1993.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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  • 2 years later...

Hello All,

          I just received an e-mail message from someone making reference to this thread with a question and referring to it as a "cliffhanger," so I thought I'd post a brief version of "the rest of the story."

          As KHE noted my car always does a leveling cycle when started after sitting overnight, sometimes more often than that, and based on the service manual this is entirely normal.

          I had a great deal of difficulty way back when in trying to source a pressure limiter valve (#5 in the diagram I posted previously) and since I had already convinced myself that the height sensor mechanism was working correctly I decided to hook up the line directly to the compressor since, at least if the height sensor is working correctly, there should never be an overpressure situation.  In the two years or so since doing this the system has been working perfectly without it.

          I think my height sensor mechanism might be set a tiny bit on the "too sensitive" side since I will consistently get a brief activation of the system if I corner hard when entering a fairly steep grade at the same time (and I live in a town of hills).  Since this activation is very brief, and it requires me to be doing something I don't do all that often, I have not been motivated to tweak the height sensor since it works just fine in every other respect.

          The De Ville is still rolling along quite happily as my daily driver and with only around 117K on her at this point I suspect she will continue to do so for quite a few years yet given her overall excellent condition.

Brian

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Bri the Tech Guy   http://britechguy.com
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"If it's got you screaming, I'll help you stop!!"
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OldCadTech,

           Amen brother!!   My philosophy is, "Don't f*ck with a functioning system!!"  (especially when probability of failure is close to zero).

Brian

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Bri the Tech Guy   http://britechguy.com
britechguy@gmail.com   (540) 324-5032
"If it's got you screaming, I'll help you stop!!"
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