[Pete315]

When I start my 94 STS, the air compressor will run for about 40 seconds then turn off. I never hear it come back on. Got no RSS codes. Car could sit for days and rear stays the same height. When compressor is on, I don't think I see the back lifting up. It almost looks like it's doing a test. Should I be concerned about this?

 

[Ranger]

Nope. That's normal, but 40 seconds sounds a little long, at least longer than mine. I wouldn't be concerned.

 

[Pete315]

I'm assuming if there was a leak, the back end would go down. Is this correct?

 

[Ranger]

Correct. Or it would never pump up.

 

[ponyboyt]

some times they have touble getting that last 1/16 of an inch up. There could be a tiny leak thats only presenting itself at that point.

 

[mhamilton]

I would take a closer look, 40 seconds is not normal. That will end up burning out the pump sooner than you'd want. The self test procedure is as follows: 30-40 seconds after key on, the pump will run for 3 seconds. That is it.

But.... If the level sensor detects that the back end is low (ie trunk is loaded up), when you turn the key on it will immediately start leveling. The pump motor self timeout is supposed to be several minutes, but I guess it could be as short as 40 seconds

So if there is no delay and the pump starts running immediately after turning the key on, the back end is too low and it is not leveling properly. I'd look for leaks.

 

[ThumperPup]

Correct. Or it would never pump up.

you forgot it also
could do a 3rd
and be pumping up all the time because its leaking

 

[ThumperPup]

pump should not run that long
maybe 20 seconds but 40 seconds thats a bit to long for it to be running
if you don;t have a leak and your never lower

then its possible the pump compressor could be on its last leg and might just be time to change it

 

[johnny kannapo]

I read these pumps are programmed to run 20 seconds then shut down & reset the cycle several minutes after due to its design needs to shut down or it will burn up.
I guess it has teflon piston rings that tells me it may operate dry.

40 seconds is a long time.

 

[mhamilton]

The FSM says that the internal timeout (controlled not by the pump itself, but by the level sensor or RSS module) is 3-7 minutes.

It does operate dry, but they will run much longer than 20 seconds at a time. That's usually how they burn out (how mine burned itself out), when there's a leak and they run for extended periods.

 

[brougham]

It could be that there is a small leak somewhere and when it raises the back it is only slightly above the normal height. So you don't notice that it's done anything and then it doesn't run again because it's timed out and shut itself down, or the leak is small enough that it would only need to run again on a long drive.

 

[Pete315]

I forgot I had my trunk loaded with heavy junk. I timed it and it was actually 25 seconds. After I emptied my trunk, I started the car and compressor ran for only 3 seconds then turned off. I just put a new compressor in last week. I changed it because the exhaust valve was shorted S038 code and after doing the test as per shop manual, the repair was to replace the compressor head. I could not find anyone that would sell just a new compressor head so I had to swap out the entire compressor. Code is gone, car feels good. Before the trunk was loaded, I never heard the compressor kick on besides the quick self check it does during every ignition cycle.

 

[ThumperPup]

cool glad to hear you figured out where the problem was and all
and that it was human eror and not a damaged parts that always good to hear
sometimes better feeling when we feel dumb about something then when we have to replace something lol