avhart

My question today is does anyone know that if a shock develops a (smallish) leak while the car is being driven will the compressor start up in an attempt to keep the shock inflated?

My experience is that it will not. If, while on the road, I notice a shock losing pressure it remains in that condition until I shut down the engine and it will only re-inflate when I start back up. Is this how it's supposed to work? I have been searching for the answer to that for a long time with no luck. I have always thought the proper and logical way would be for the compressor to start whenever a sensor goes out of whack but I can't find info on that detail anywhere so I can't tell if my suspension system is working properly or not.

Any help would be much appreciated...and thanks in advance.

Yamae

The Celsior's manual for UCF21 only shows this about the compressor and the relief valve's function and how to check them. I just translated the contents originally written in Japanese.


How to check.
Set the height control switch Normal.
(1) After turning the ignition witch OFF, 4 people weighted about 55kg each, ride in. 2-in front, 2-rear.
(2) Start the engine and measure the time length.
Within 2 seconds, the compressor should start to work.
The compressor works for about 20 to 40 seconds.
(3) Turn OFF the engine and 4 people ride off.
(4) Start the engine and measure the time length.
Within 2 seconds, the relief valve should start to work.
The relief valve works for about 20 to 40 seconds.

avhart

Thanks Yamae,

By any chance does it give at what pressure the relief valve should go off?

cj98ls

I believe the pressure relief valve is controlled by the computer via the height control sensors at each wheel.
According to the block diagram in the repair manual this is the way the system is supposed to work. The height control sensors tell the computer that the ride height is too low, the computer starts the air compressor and opens the valves to the struts allowing the air pressure to lift the vehicle to the correct height, then the soleoids close the valves and the compressor shuts down. If the vehicle is too high, the computer signals the solenoids to open the valves to the struts and to the pressure relief valve, allowing air pressure in the struts to drop until the ride height is "corrected" to the proper height, then the valves, including the pressure relief valve, are closed again. The pressure relief valve is the only outlet for the system, so needs to be open when the system vents air.

CELSI0R

I'm not sure this will be of much help, but these are the Toyota Service Training videos for the Air Suspension system. I haven't watched them in depth, but it should discuss the operation of the system:

EDIT: The second video from 6:00 onwards may be of particular interest to you, but the core background is in the beginning of the first video.

avhart

Hi CELSIOR,

Those look like two most excellent videos and they contain information that I have always been interested in regarding the Air Sus operation. I will look at them carefully and report back as to my thinking. Regardless whether they will address my question or not I don't know yet but in any case they have already proved very useful for my understanding of how that system works.

Thank you very much indeed ...

cj98ls

As to your question about the small leak, I guess it depends on how small a leak it is, if what I understand from the videos above about the height sensors with their 16 height values is any indication. If your leak allows enough air to escape to change a sensor reading from one height value to the next, say eight to seven, then I would guess that the compressor would engage and the valve controlling the strut closest to the changed sensor would open and inflate that strut until the sensor reached the appropriate height value. I would think that would happen whenever the system is energized.

avhart

Yes that's what I thought as well but as far as I can tell, it doesn't work that way on my car. So I was trying to get an answer to that specific question but it's proving elusive lol.

There is also more going on there than meets the eye. Let me explain. One time my car was not starting due to a fuel pump issue and that same problem shock (right rear) deflated. So I thought that if I could get the compressor to activate I would be able to pump it back up - but no. I followed precisely all the instructions in the manual how to jump the connector to the suspension ECU and did indeed get the compressor to come on BUT it still did not inflate the shock.

So I suppose that means there is some solenoid or switch that does not open when the engine is not running because just as soon as the engine started with a new pump a few days later the shock pumped right back up as normal.

EDIT - I had just finished writing this when a thought struck me. To turn the compressor on I had to pull out that same suspension ECU connector to put in the jumper and therin is where the solution to that problem may lie. But then that will bring up another can of worms. Can i jump the pins when the connector is plugged in without causing any damage?

So the quest goes on....

cj98ls

Have you tried just turning on the car without starting the engine and seeing if the compressor comes on and inflates the saggy strut?

avhart

Oh yes. That would have been a perfect solution but nope - it don't . The engine has to be running....weird

cj98ls

Seems odd to me too, but the engineers who put the system together probably had a reason, maybe current draw of the compressor...

avhart

Ah yes - I didn't think of that. Quite possibly that is as good an explanation as any. I can even understand where it would be ok to run at idle, like when you jumper the pins, but it's a whole different ball game when it has to actually work. It'll draw a whole lot more current then. The more I think about it the more right it sounds.

So apparently we are back to the original question as to if it's supposed to come on when the car is being driven with a leaking shock.

CELSI0R

I just watched the video. Based on it, I would believe the answer is yes - the car should self level always to the specified height

When you notice the car start to sag, have you tried switching the height setting to see if the car adjusts to that level?

I wonder if the sensor is reading properly for the corner that is loosing pressure

avhart

Thanks for your reply CELSIOR. Well it has happened already that the shock began losing pressure while I was driving and the compressor did not kick in to restore the height. And yes I did indeed try the High/Normal switch and it didn't seem to make a difference (while driving). Yet as soon as I parked up somewhere and shut down the engine, upon restart it pumped up just fine.

I have also thought of putting the blame on the RH height sensor and that is still an open question. The sensor itself is obviously working because it does pump up the shock to the appropriate height (High/Normal) upon restarting. I am beginning to think that maybe the shock itself is totally screwed up internally and that is what is causing the problem. In light of that I have just purchased a supposedly good used shock from a reliable supplier in Japan so I guess it would make sense to leave this discussion until I install it and report back.

It was a pleasure discussing my problem with all you guys and I really appreciated all the input and I have certainly learned a whole lot. I have been helped immeasurably by any number of different members of this forum which is really vital for me because there is no real competence regarding these exotic older cars where I live in Trinidad. I'll be back....

Thanks again to everyone.