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2005 gmc envoy_slt_xuv
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Discussion Starter · #1 · (Edited)
recently my 2005 Envoy XUV was in to the dealer b/c its azz was on the ground every morning. Since I just bought it and its certified used, back to a different local dealer it went (bought out of state) where they were perfectly happy to change out the compressor for me, even though I assured them the compressor works fine (and also that GM service history from prev. owner shoed it being replaced less than 1 year/ 1200 miles ago) - the bags pump back up and the compressor cycles to keep them up when running - but they insisted me the tech said it was the compressor.

They called, "all done - come pick it up" and I said keep it overnight and call me in the morning after you see that its all right. They called the next day and said "well, we just ordered 2 bags ... ". I told them to have the tech check every line and fitting when doing the bag job b/c I DONT want to have to bring it in a 3rd time.

So, after their come N' get it call, again I said keep it overnight and the next day everything was dandy. I brougnt it home and let it sit 2 days and on day 3 the pump only cycled about 3-4 seconds on start-up.

Here's where I'm going with this whole story / question - I'm planning to tow my race car in 2 weeks and yest. borrowed my friends' trailer. While the empty trailer was attached (and stationary / on flat pavement) I noticed several times the compressor coming on for 4-6 seconds over the course of say 5 minutes

IS THIS NORMAL ?? Does the system need to cycle every so often or (as Im thinking) it shouldn't have to and I've still got some small leak somewhere.

Im going to be towing close to 500 miles each way and obviously dont want to burn it out or have troubles on the road ...

Thanks
 

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2002 gmc
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I would say this is normal. When I hook my boat up with a 400 pound tongue weight, it will continue to adjust beyond the initial hookup. I think this is because of variations in incline and road surface, and the body level sensor is just trying to compensate. For the most part once you're trailering on the road it won't adjust. As soon as you stop though, say at an intersection that is at an angle, expect it to level again.
 

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2002 gmc envoy_slt
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The cycling is totally normal.

The dealership probably replaced the pump, even though it was inflating fine, because it has an air release check valve that goes bad and is not serviceable beyond replacing the whole compressor ;) So dont think they were just "throwing parts" at it. Ive replaced my compressor 3 times in my 2002 Envoy, once was because the check valve went bad and it would deflate overnight, or during the workday I'd come out to my truck and it would be low-riding.

Mine will run every start up for a few seconds. I hear it cycle while Im at red lights, drive thru's, parking, etc... Its the nature of the beast :m2:
 

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2005 gmc envoy_slt_xuv
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Discussion Starter · #4 ·
Thank You both for your replies. Interesting that the release valve is in the pump and non-servicable - While mine was azz-down I realized two things (being 5'7" tall....)

A) how much easier it is to wash
B) how much easier it would be to load the Thule rooftop carrier

I may be looking to hook up a manual deflate switch/valve in the future

As an update, I called the dealer and told him of my concerns and he said bring it in. All weekend it was bothering me so yesterday afternoon I decided to set about doing some semi-scientific testing.

With the XUV turned off and the truck and trailer (detached for the moment) perfectly flat and level in my driveway I laid a T-square against the back bumper as close to vertical as I could and measured at my point a resting height of 22".

I then took a 55 gallon garbage can and put it on the trailer tongue as close to the hitch as possible and filled it with water (55gal x 8.3lbs/gal = approx 450 lbs). I then lowered to trailer onto the hitch and it compressed down to a height of just under 18".

I then turned the XUV on and the compressor ran for a good 45 seconds raising the measuring spot back up to 21 3/8" - not bad !!. I let it sit running for a good 10 minutes and it did not cycle again.

Then, I turned the engine off but left the ignition in "run" (the system still functions the same but you can hear it better) and used the trailer jack to quickly take the weight off the hitch measuring 25" until about 15 seconds later when the release valve opened and it deflated down to 22.5".

I then played several times (with my wife rolling her eyes and saying "the neighbor's already think you're crazy - do you have to prove them right ??") with raising and lowering the weight on and off the hitch.

It seemed a minimum of 3/4" drop was necessary for the compressor to come on after an interval of about 15-20 seconds. What was interesting was that if I quickly dumped the weight on this interval did not speed up so it was possible to have the compressed height change quite a bit for those seconds with no activity of the system. It was also interesting to note that the resting height could vary by as much as half an inch without further deflating/inflating when left static.

As a last and final test I put the full wieght on the hitch, let the system stabilize for 10 minutes (only one minor inflate adjustment of about 3-5 seconds early on) and let it sit from 9:30p until 7a this morning ....

... and Im happy to say the recorded ride height did not change more than 1/8th of an inch, which I'll account for variables such as nitetime cooling and measuring inaccuracies leaving me to believe that all is well
 
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