Not building air at idle

[Russ Knight]

Searched forums with no luck. M925A2 not building air at idle. At speed, truck builds air and compressor cycles off at 130+ psi. Complete air dryer service within the last 6 months. No leaks detected. Could it be the PPV valve?

 

[Russ Knight]

Also replaced the unloader valve with new a few months back.

 

[simp5782]

Also replaced the unloader valve with new a few months back.

You need to pull pressure off the back of the head at idle so you need to attach a gauge right off the discharge port there.

Sometimes the discharge tube can get crammed full of crap but wont let much air thru at idle

Sent from my SM-G965U using Tapatalk

 

[Elijah95]

I had a severe case of the blues on my M923A2 8.3 truck with air pressure, at the ga rally my air seemed like it was struggling to build, almost non existent at 700rpm and very slow at 1200 rpm, moderate at 2000. What I later discovered when I broke down was my head gasket on the air compressor was failing, and eventually just failed and left me without air.

That should be a holset SS296 compressor iirc, order a gasket rebuild kit with stuff to also do a minor rebuild on the unloader on the top. Should be no more than $30

Speaking of which, your unloader may be sticky, partially preventing building air as it should when you’re at idle. Take the top air line off (signal line) and shoot air tool oil in it, and hit it with compressed air several times, you’ll hear it click clack as you add and remove air actuating

 

[Russ Knight]

I had a severe case of the blues on my M923A2 8.3 truck with air pressure, at the ga rally my air seemed like it was struggling to build, almost non existent at 700rpm and very slow at 1200 rpm, moderate at 2000. What I later discovered when I broke down was my head gasket on the air compressor was failing, and eventually just failed and left me without air.

That should be a holset SS296 compressor iirc, order a gasket rebuild kit with stuff to also do a minor rebuild on the unloader on the top. Should be no more than $30

Speaking of which, your unloader may be sticky, partially preventing building air as it should when you’re at idle. Take the top air line off (signal line) and shoot air tool oil in it, and hit it with compressed air several times, you’ll hear it click clack as you add and remove air actuating

Just replaced the head gasket and unloader valve about three months ago.

 

[Elijah95]

Just replaced the head gasket and unloader valve about three months ago.

Did you check the head for flatness? Other members (myself included) have experienced minor head warpage which is enough to cause premature head gasket failure, last time I removed mine for head gasket number 2 I took a large flat file and very carefully decked the head until flat.

A flat table and large sheet of sandpaper also works great too.

 

[Elijah95]

Just replaced the head gasket and unloader valve about three months ago.

Both gaskets? The actual head gasket that is exposed to the compressor piston and the unloader flat paper gasket?

 

[98G]

Just replaced the head gasket and unloader valve about three months ago.

I suspect the unloader is full of water....

 

[Russ Knight]

Both gaskets? The actual head gasket that is exposed to the compressor piston and the unloader flat paper gasket?

If I remember correctly, the unloader had an o-ring seal. Everything was replaced. Sprayed the compressor with soapy water, no visible leaks. Shot a dose of Aerokroil in the line from the governor. I'll run it some and see what happens.

 

[Elijah95]

If I remember correctly, the unloader had an o-ring seal. Everything was replaced. Sprayed the compressor with soapy water, no visible leaks. Shot a dose of Aerokroil in the line from the governor. I'll run it some and see what happens.

Yes it does have and O ring seal on the top half. But there’s the actual head gaskets here, top left is the unloader “head gasket” and the bottom right is the actual compressor “head” gasket.

Top left goes between the unloader plate and physical head

Bottom right goes between the compressor head and “block”/cylinder

On mine the top left gasket had cracks in it, which then allowed air to flow freely between the intake and exhaust side of the compressor gradually getting worse until I no longer had any air pressure.

 

[Russ Knight]

Yes it does have and O ring seal on the top half. But there’s the actual head gaskets here, top left is the unloader “head gasket” and the bottom right is the actual compressor “head” gasket.

Top left goes between the unloader plate and physical head

Bottom right goes between the compressor head and “block”/cylinder

On mine the top left gasket had cracks in it, which then allowed air to flow freely between the intake and exhaust side of the compressor gradually getting worse until I no longer had any air pressure.

I can't get the link to open.

 

[Elijah95]

I can't get the link to open.

pm sent

 

[Elijah95]

How’s the status report

 

[Russ Knight]

I've been busy at work, haven't had time to mess with it. Hopefully I'll have time to monkey with it this weekend. While on the topic, does anyone have a part number for a two stage compressor for these trucks?

 

[Elijah95]

I've been busy at work, haven't had time to mess with it. Hopefully I'll have time to monkey with it this weekend. While on the topic, does anyone have a part number for a two stage compressor for these trucks?

From what I hear, our compressors are more than adequate, but our tanks fall short. Talk to Simp about how adding air tanks changed the nature of the beast

 

[Russ Knight]

Welp, found the problem. Brand new compressor head gasket is leaking significantly. Is it possible to remove the head without removing the compressor?

 

[Elijah95]

Welp, found the problem. Brand new compressor head gasket is leaking significantly. Is it possible to remove the head without removing the compressor?

For sure! It’s a little tight, but drain the coolant, pull the bolts and pop it off. Have it and the unloader head machined flat and reinstall. It’s a 2 hour job taking your time

 

[Russ Knight]

Thanks! I think I’ll take the front tire off to make it easier as well.

 

[Elijah95]

You can do that, I had real good luck just lifting the fender liner out and using the tire as a seat. Lol