New M1089 FMTV owner

[wandering neurons]

PM me. I've got my old parts

 

[319cssb]

If I'm correct, I think on a working sensor there should be continuity between pin B and A should out of range on an empty tank. And on pressure there should be a resistance.

 

[Suprman]

Tank switch or pressure sender on pneumatic valve?

 

[319cssb]

Tank switch or pressure sender on pneumatic valve?

The variable pressure sender.

 

[Suprman]

I believe its a resistance based sender. Higher pressure equates to more resistance. I could have it backwards though.

 

[319cssb]

I believe its a resistance based sender. Higher pressure equates to more resistance. I could have it backwards though.

that's correct, But it also has a shut off. If there is no pressure it won't even switch any resistance.
Therefore, unless system pressure is building it won't even turn the CTIS on. Once the ECU senses a change it monitors the values. or throws an error code.

 

[wandering neurons]

I think that the ECU, when it first powers up looks at the pressure transducer even before there's air pressure. That's why my ECU was throwing a fault whether I was using the engine compressor or shop air to supply air. With the engine compressor, it'd take a minute or two for pressure to come up to 120 psi, but the ECU would fault after two flashes of the HWY light. With shop air, I'd have the pressure already at 120 psi and connected to the truck before turning on the main power switch, which means that the ECU would immediately see 120 psi from the wet tank. Hence, there's Power-on Self-Testing (POST) in the ECU just after the main power is turned on. If the pressure transducer is not working (reading ambient air pressure), it'd fault the ECU. I think that it's too early in the POST for the pressure transducer to see anything over ambient, as the lines to the quick-reaction valves should still be vented to atmosphere, that'd happen after the wet tank reaches 120 psi and the ECU commands the PCU to check the solenoids, then read tire pressures.

Sanity check, please?

that's correct, But it also has a shut off. If there is no pressure it won't even switch any resistance.
Therefore, unless system pressure is building it won't even turn the CTIS on. Once the ECU senses a change it monitors the values. or throws an error code.

 

[319cssb]

Do I understand it correctly, that to drain the air dryer and 'make sure it's not clogged' involves a 5/16 square drive?
I don't know how else to make sure it's not clogged

 

[Suprman]

Which dryer do you have? Is it the tube with fins or the purest style? The purest ones you replace the cartridge it’s under a black metal cover on top held with 4 bolts. If it’s the tube with fins replace the whole thing with a purest style one.

 

[319cssb]

Which dryer do you have? Is it the tube with fins or the purest style? The purest ones you replace the cartridge it’s under a black metal cover on top held with 4 bolts. If it’s the tube with fins replace the whole thing with a purest style one.

I have a 2006 M1089A1, they only come with one style of airdryer in those years . The finned type was a thing of the 90's, if I'm not mistaken.

i was asking about
a) how to drain it ( think by using a 5/16 square drive)
b) how to make sure it's not clogged

then I can still decide whether I need to replace. But first I need to know if I even have to.

 

[Suprman]

I have 2003s that came with the fins style. The purest takes a rn60z cartridge.

 

[319cssb]

How do find out whether I need to change it?

 

[Suprman]

I would just change it. Only around 75 bucks online. Comes with the o ring also.

 

[scottmandu]

I have a 2006 M1089A1, they only come with one style of airdryer in those years . The finned type was a thing of the 90's, if I'm not mistaken.
i was asking about
a) how to drain it ( think by using a 5/16 square drive)
b) how to make sure it's not clogged
then I can still decide whether I need to replace. But first I need to know if I even have to.

The Newer driers appear to be a change made when the C7 was used, so late 2004 and newer.

 

[319cssb]

I would just change it. Only around 75 bucks online. Comes with the o ring also.

I have a gazillion things I need to go through, still. And If the air dryer filter doesn't need to be one of the things I have to spend money on right now, I'd prefer not to.
Still got to change all fluids, filters. get the transmission fluid changed to OEM Allison recommended fluid and so on and so on.

Does anyone know How to check if the air dryer is clogged? I get a bunch of water coming through the tanks when I drain them.

 

[coachgeo]

...Does anyone know How to check if the air dryer is clogged? I get a bunch of water coming through the tanks when I drain them.

guess all you can do at this point is just pull the dryer/filter out and see what it looks like? Lot of water certainly seems to say something is amiss there. I don't get any but mine still freezes when real cold..... grrrr.

 

[Johno176]

With that Purest air dryer you should see very little if any water come from the tanks. I installed a new one when I got my truck and have never seen any water in the tanks. As far as the unit being clogged, you should hear the unit purging on a regular basis and see the water spray coming out.

 

[319cssb]

I do get a signal spray when the system reaches pressure. If the truck never had the tanks drained , then there could be a lot of water in the system. A sham shields mission is to do the least amount of work possible. Ask me how I know.

 

[319cssb]

So thanks to all of your help, some troubleshoot and most importantly thanks to NV555, the CTIS came back to life.
just as we assumed already, it was the pressure sensor, which is mounted at the valve block.
update: with the CTIS working, the air dryer purges a lot more. Maybe that will take care of the excess water