Air Suspension - problem and diagnosis

[Chef]

I've been reading a number of threads on this topic since some problems I had earlier today and have found some good information. But I'd like to run some questions here first.

 

Background:

 

I purchased my 92 legacy wagon with the air suspension about a month ago. Pressing the height button never seemed to raise the vehicle, but the struts appeared to be inflated fine and no sound of leaking apparent. Right from the start, the height button would begin to flash for extended periods once in a while after driving for 15 - 30 minutes, and shut off after restarting. Sometime it would come back on after another 15 - 30 min, sometimes not at all. Usually only with city driving, but I did notice sometimes on the highway the car seemed to almost shimmy or "waddle" with slightly decreased ride quality. It did not pull to the side (generally), and I chalked it up to poor roads and possibly worn ball joints.

 

I drove out for about 3 hours this weekend only to have the light begin flashing at highway speeds after about 30 min. It shut off when restarting the car. On the way back from my trip, it was on most of the time. After stopping for a bite and returning on my drive, I noticed the car seemed somewhat low on the right front wheel, but chalked it up to being parked on a slant putting the weight on that side of the car. After leaving, it began flashing within 10 - 15 minutes. During the last 30 min of the trip I noticed the ride seemed much harsher, and somewhat lower on that side. After stopping to take a look (leaving the car running), it was apparent the strut was entirely deflated, as there was little clearance at the top and pushing on it yielded no compression.

 

I began to drive again carefully, and the bumps were a bit harsh. After a 15 minute drive to my final location, I noticed the bumps were fine and the strut completely inflated again. Another drive later tonight found the strut to be fine again, with no light flashing.

 

Diagnosis:

 

I assumed at first the strut must be leaking. But this makes little sense, because it seems to reinflate fine, and generally is not uninflated (although perhaps in the low position sometimes). It could be an intermittently leak I suppose, but I don't know.

 

So after much reading here and finding the diagnostic guides, I did a little guess work. I have not had an opportunity to check for codes yet - maybe tomorrow.

 

http://www.ultimatesubaru.org/forum/showthread.php?t=27654&page=2&pp=10&highlight=air+suspension

 

http://endwrench.com/images/pdfs/AirSuspSumm01.pdf

http://endwrench.com/images/pdfs/AirSuspenFall01.pdf

 

 

So my thoughts are this. I believe it may be a faulty solenoid valve in the right front strut, causing it to move up and down regularly because the ECU finds no fault but keeps compensating. This idea stems from this in the second guide:

 

Valve Stuck Open

If a strut solenoid valve sticks open,

the following sequence of events will

occur (example deals with a right front

strut valve):

• When the control unit tries to raise the

rear of the vehicle, the right front strut

also raises.

• Soon the right front strut height sensor

reports that it is too high.

• Because control unit logic commands

“lower before raise,” the control unit

stops trying to raise the rear and

begins to lower the right front strut.

• When the right front strut height sensor

reports that it has been lowered to

the normal position, the control unit

once again begins trying to raise the

rear.

• Again the right front strut raises along

with the rear.

This process can continue indefinitely.

The system would not recognize that a

fault existed. The owner might report

that the compressor seems to be running

a lot.

 

Sounds plausible. Could also be a defective pressure switch, but I doubt it because the problem seems only to occur on the front right strut. I will check into this.

 

Any thoughts? Can the solenoid be purchased new separate from the strut? Or is my only option a solenoid from the wrecker?

[Chef]

Not a popular topic this air suspension, eh?

 

I should also mention it seems the compressor is running a lot as well - I think.

 

I've checked out my options for replacement of the entire system to a regular spring/strut system, but it's simply not feasible money-wise right now - Perhaps in the near future. Legacy central has a good sticky thread noting which suspensions will work with legacys, and apparently anything from a legacy up to a 99 will bolt right on, and so will imprezas from 1993 - 2002. So this is a plan for the future, but not for now.

 

Some advice would be much appreciated.

[firstwagon]

Not a popular topic this air suspension, eh?

 

I should also mention it seems the compressor is running a lot as well - I think.

 

I've checked out my options for replacement of the entire system to a regular spring/strut system, but it's simply not feasible money-wise right now - Perhaps in the near future. Legacy central has a good sticky thread noting which suspensions will work with legacys, and apparently anything from a legacy up to a 99 will bolt right on, and so will imprezas from 1993 - 2002. So this is a plan for the future, but not for now.

 

Some advice would be much appreciated.

 

I wish I could help but I'm learning more from your first post then I already knew. Here's all I know so far....

 

I bought my 91 Legacy wagon with a leaky air suspension but in my case it turned out to be rotted rubber on the airbags themselves. The drivers side had a large split in it and was slowly leaking air. At first it would deflate over night but re- inflate when I drove it and was fine for the day. Within a couple weeks the leak got to the point where the compressor could not keep up with the leak and I had to fix it. I picked up a used strut from the wreckers and $150 Cdn and it took about 1 hour to install it. Everything works now but I will likely install a coil suspension too if I get some extra money in the next year.

 

A leaky bag is easy to find. When it's inflated, squirt some windex on it and watch for the bubbles. Even a very small leak should show up this way. This might also work for the solenoids if it's leaking to the outside as opposed to through the system.

 

 

Good luck and thanks for sharing your research...

 

Paul

[Chef]

No problem. This seems to be a issue for a small number of individuals that has few noted remedies.

 

I tried to get the codes today, but for some reason it wouldn't enter the diagnostic mode after following the directions given in the manuals noted above.

 

But I did get something new. It raised when the button was activated. I pressed the button with the car in the on position, and I heard the compressor activate. It ran for about 5 minutes or so, and the car raised to the high position. Then it shut off, and the car remained high. I measured the height from the centre of the wheel to the top of the fender and it was consistent all around. It remained that way even after turning it off. Eventually the light began to flash indicating an error, but the height remained high. After driving for a bit at 70 - 80 km/h, it seemed to return to the normal position, but the light kept comingon and flashing after 15 min of driving.

 

I'm not so certain now it's the solenoid, unless it's intermittently sticking. It could be a height sensor too.

 

I will try the windex tomorrow and see if it bubbles. The bag in the front right side definitely has some fine cracks in it. Maybe it's just leaking afterall. I will try to score a new strut from the wreckers if possible.

 

 

I wish I could help but I'm learning more from your first post then I already knew. Here's all I know so far....

 

I bought my 91 Legacy wagon with a leaky air suspension but in my case it turned out to be rotted rubber on the airbags themselves. The drivers side had a large split in it and was slowly leaking air. At first it would deflate over night but re- inflate when I drove it and was fine for the day. Within a couple weeks the leak got to the point where the compressor could not keep up with the leak and I had to fix it. I picked up a used strut from the wreckers and $150 Cdn and it took about 1 hour to install it. Everything works now but I will likely install a coil suspension too if I get some extra money in the next year.

 

A leaky bag is easy to find. When it's inflated, squirt some windex on it and watch for the bubbles. Even a very small leak should show up this way. This might also work for the solenoids if it's leaking to the outside as opposed to through the system.

 

 

Good luck and thanks for sharing your research...

 

Paul

[firstwagon]

Here's the newest thing I found...

 

If you leave it in the raised position and shut the car off, will it remain in the position? Since I replaced the one front strut my suspension is always inflated normally. However last weekend I shut it off in the raised position and left it overnight. In the morning the left rear was in the high position, the left front and the right read seemed to be in the normal position and the right front was bottomed out. I started the car and switched the height off. The rear came down right away and the front slowly started to rise. Within a few minutes it was back to normal and has stayed that way. I would have thought you could leave it raised and it would stay there whether the car was running or not.

 

Should I always lower the car or something wrong?

 

So much to learn and I would be going nuts if it weren't for these forums.

[Chef]

Mine stayed raised in the high position when off overnight. You didn't accidently bump the height button perhaps?

 

The ECU logic tells it to lower before raising, so that's why the rear dropped before the front. But why it remained high and the front dropped, I don't know. Especially interesting the right front bottomed out.

 

This is rather aggravating stuff, isn't it?

 

Another thing I've noticed is that my right rear seems rough, always bumping harshly despite being inflated normally. All others seem fine though.

 

I wonder now if my rear is moving to the normal position at all, or simply remaining high. I need to check and measure this.

 

Sigh. Need to replace the front rotors this weekend, as I'm getting bad vibration while braking.

 

Here's the newest thing I found...

 

If you leave it in the raised position and shut the car off, will it remain in the position? Since I replaced the one front strut my suspension is always inflated normally. However last weekend I shut it off in the raised position and left it overnight. In the morning the left rear was in the high position, the left front and the right read seemed to be in the normal position and the right front was bottomed out. I started the car and switched the height off. The rear came down right away and the front slowly started to rise. Within a few minutes it was back to normal and has stayed that way. I would have thought you could leave it raised and it would stay there whether the car was running or not.

 

Should I always lower the car or something wrong?

 

So much to learn and I would be going nuts if it weren't for these forums.

[Chef]

Okay, I've been monitoring the height of thge vehicle for a while, and it seems to be rather variable. After shutting off the height by travelling over 85 kmh, the front dropped to the normal height within a short period while the rear remained in the full height position for a couple of days before dropping to the normal height. I measured the high position to be 17" from the centre of the wheel to the top of the wheel well, while the normal position appears to be about 15.5". Sometimes they seem to sit around 16".

 

This is quite confusing, and makes me wonder if the ECU is possibly even at fault. Another thing is that the right rear strut appears to be much harsher than the rest, despite appearing properly inflated.

 

Grrr...

 

 

Mine stayed raised in the high position when off overnight. You didn't accidently bump the height button perhaps?

 

The ECU logic tells it to lower before raising, so that's why the rear dropped before the front. But why it remained high and the front dropped, I don't know. Especially interesting the right front bottomed out.

 

This is rather aggravating stuff, isn't it?

 

Another thing I've noticed is that my right rear seems rough, always bumping harshly despite being inflated normally. All others seem fine though.

 

I wonder now if my rear is moving to the normal position at all, or simply remaining high. I need to check and measure this.

 

Sigh. Need to replace the front rotors this weekend, as I'm getting bad vibration while braking.

[Chef]

So after a 1.5 hr highway trip the right front strut deflated fully again (more or less). I think it occurred within the last 30 minutes or so,although the height light flashed 15 min after leaving.

 

After arriving, shut the car off and left it in the on position, and pressed the height button. The compressor activated for about 30 sec and then quit. The strut did not rise, nor did the others.

 

So later I drove out to pick up a movie, and the strut was still deflated upon arrival (~15 min). On the drive back, the RF strut then rose to the high position, probably within a couple of minutes, and the rest of the struts rose to the high position. All struts were still in the high position after sitting overnight and now driving a bit today.

 

I'm quite confused. Why does the one strut keep deflating after extended ride periods? The compressor didn't even go on afterwards.

 

Basicallly I'm ruling out a leak at this point. I can only think that the problems may be:

 

-Faulty solenoid valve on RF strut

-Faulty height senor on RF strut

-Faulty height sensor on rear struts, indicating too low and dropping the front to compensate

 

It may also be more than one thing at fault, including a problem with the compressor.

 

I am going to look in getting rid of this air system. By the time I have a dealer diagnose the problem and get it taken care of,I may be out more money than finding used replacement spring struts and installing them.

[idosubaru]

i'm guesssing orings, compressor leaking or leaky strut.

 

one strut is leaking. try the o-rings at the associated solenoid. best bet is to replace all the o-rings in the entire system. one dollars worth of new orings can solve major problems (leaks). there are two orings at each solenoid. don't bother trying to find a part number or anything. remove an oring and go to an auto parts store and have them match up the right size. apply a little grease to the new orings and install.

 

now that the orings are addressed another possibility is the air compressor. if it's running alot, that's not good as it will wear out. on the air compressor are fittings for receiving the air lines. these fittings can become loose or cracked and basically fall off or just hang there. it will be obvious if this is the case. don't bother repairing them, get a new compressor or just the part you need if you can locate it.

 

air strut and computers are possibilities but if the air struts aren't all rusted and terrible looking i'd check the first things i mentioned. this air suspension is relatively simple to work with and not that bad for those of us that horde extra parts. keep rust off the struts and they'll last a very long time, i never have to replace them. i wire brush the rust off of them and paint them flat black. the rust will rub against the rubber bag and wear the rubber out.

 

i replace my orings, keep the struts rust free and have few problems. bought my XT6 at 105,000 miles and 4 years later at 215,000 with the same struts and no problems. they appear in great shape and i don't see them failing any time soon.

[Chef]

Thanks, I'll check into this. I suspect the strut itself isn't leaky as it holds air overnight (or longer) fine. The only time it deflates is during driving, and even then only intermittently.

 

Thanks a bunch for the suggestions.

 

Chef

 

 

 

i'm guesssing orings, compressor leaking or leaky strut.

 

one strut is leaking. try the o-rings at the associated solenoid. best bet is to replace all the o-rings in the entire system. one dollars worth of new orings can solve major problems (leaks). there are two orings at each solenoid. don't bother trying to find a part number or anything. remove an oring and go to an auto parts store and have them match up the right size. apply a little grease to the new orings and install.

 

now that the orings are addressed another possibility is the air compressor. if it's running alot, that's not good as it will wear out. on the air compressor are fittings for receiving the air lines. these fittings can become loose or cracked and basically fall off or just hang there. it will be obvious if this is the case. don't bother repairing them, get a new compressor or just the part you need if you can locate it.

 

air strut and computers are possibilities but if the air struts aren't all rusted and terrible looking i'd check the first things i mentioned. this air suspension is relatively simple to work with and not that bad for those of us that horde extra parts. keep rust off the struts and they'll last a very long time, i never have to replace them. i wire brush the rust off of them and paint them flat black. the rust will rub against the rubber bag and wear the rubber out.

 

i replace my orings, keep the struts rust free and have few problems. bought my XT6 at 105,000 miles and 4 years later at 215,000 with the same struts and no problems. they appear in great shape and i don't see them failing any time soon.