M1078 fmtv ctis

[captkennyboy]

hi all I have a 1995 M1078. the tires hold air pressure but the highway light flashes on the console. If I press another setting nothing happens but the light flashes.

Any ideas on were to start. I have not found any air leaks

thanks

 

[Lmtv772]

Mine blinks when I start the truck, once the air tanks are filled the CTIS builds pressure and then fills the tires, if needed. Then the light turns solid.

 

[captkennyboy]

that's usually the case with my other trucks however the tires are at 60 pounds. I filled them manually and they hold pressure with no leaks for weeks but the CTIS seems to do nothing meaning not filling or lowering the air pressure????

 

[Suprman]

If the highway light just flashes from startup until the air tanks are full then its not recognizing that the air tanks are full so it can do its initial pressure check. The LMTV system is very similar to the M939A2 system. There should be a pressure switch somewhere. Do both tanks reach 120psi? It may just need the air governor turned up slightly to trigger the switch. Or the air switch could be bad/bad wiring.
Will

 

[Lmtv772]

If the air system is leaking badly, it will do what you describe. Also check the pressure protection valve, if it's leaking the outranks won't build pressure and if it's clogged/installed wrong the CTIS won't build air pressure.

 

[dalej]

Is there a way figure out why my CTIS is not working? I have owned the truck for 2 months now and when I started it, I could hear a noise under the cab and the 5 lights would blink and then would switch to one (hwy) and then it would finally turn solid.

Now, when I start the truck, the five lights blink once and then go to the one (hwy) and it blinks all the time. I don't hear the noise of what I think is the control valves working.

Any thoughts on what to look for?

 

[Suprman]

Same as above. If the ctis controller does not get a signal (switch close I believe) from the pressure switch that tells the system the tank pressure has reached 120 psi nothing will happen and hwy will just flash. It is waiting to do an initial pressure check but is designed not to take air from the brake system when pressure is below a certain level.

 

[dalej]

Is there a way to bypass the pressure switch for diagnostics?, there are 3 contacts. My air tanks are full. In the relay/fuse panel, there is a relay marked ctis overdrive, does it do anything? I can't feel the relay engage when the switch is turned on before the engine start. The other breaker does light up the ctis lights.

 

[Suprman]

That is the pressure transducer. It tells the system what the tire pressure is when the system does its pressure check. The tank pressure switch would be on the 3rd tank probably.

 

[Lmtv772]

Is there a way to bypass the pressure switch for diagnostics?, there are 3 contacts. My air tanks are full. In the relay/fuse panel, there is a relay marked ctis overdrive, does it do anything? I can't feel the relay engage when the switch is turned on before the engine start. The other breaker does light up the ctis lights.

I think you should do a whole lot more reading before you mess with relays and pressure switches.
Did you check the pressure protection valve, yet? if that thing is clogged or installed backward it won't fill the CTIS tank.

That is the pressure transducer. It tells the system what the tire pressure is when the system does its pressure check. The tank pressure switch would be on the 3rd tank probably.

correct, see my post #5

 

[dalej]

Ok, My CTIS is working again. Here is a rundown of what I did. First and foremost I had to identify the pressure
switch that everyone was talking about. Mine is right above the CTIS supply line on the wet tank.


I then separated it and marked it with red dots for aligning it so I could connect it and disconnect it really fast several times after applying cleaner and then the Dielectric grease.


I then did the same on the connectors at the CTIS controller and the connectors at the manifold. Here are also photos of the products that I used.

 

[tokarev]

Mine acts like you described - will have to do the same.

 

[awind]

I have the same problem with mine. Highway flashes continually. I have replaced all electronic components from known working trucking. (Manifold, ECU, Pressure switch) with same results. On a different truck: How do the valves on the tires work. I had a truck that the hose bolting to the wheel stud was disconnected and tire was not losing any air. Check valve? How does the deflate system work? I hear air releasing from a valve under truck. What opens that? When the CTIS works its great but complicated to figure out.

 

[Suprman]

Its a mechanical system. The valves have rubber flappers with springs to stay closed. Fill air comes out the cab valve body and gets split off to the axles then to the wheels pushing past the flappers to the tires. The system should self equalize if one tire is lower than others. To dump the system send 16psi I think it is and that is just enough to hold open the flapper and allow air to dump.

 

[awind]

So, Higher pressure to fill and then lower pressure to hold the valves open? This valve is the regulator on each wheel?

 

[Suprman]

Higher pressure fills and the set low pressure holds the valves open to dump air. Down to at least the dump pressure it shouldnt go down past that.

 

[awind]

So I have an issue that the tank that the CTIS pressure switch is on only builds to 110 psi. The switch does not close till 120 psi (based on my other truck). The gauges read 120psi on the dash. How is it that the last of 3 tanks only builds to 110psi? Is there a separate regulator for the 3rd tank?

 

[Suprman]

Turn the air governor up a tad. It's normal to have the pressure slightly different from tank to tank. The governor is on the compressor drivers side of the engine.

 

[tjhuffy]

I just purchased my M-1078 a couple of weeks ago, and the control box on the dash was missing. After reading several posts on how the system wasn't the most reliable, I decided to go the manual route with a regulator and some gate valves. For me it works fine, and I can set my tires at any pressure. If you would like more info let me know.

 

[Suprman]

The wheel valves and hub seals are the most problematic of the system. I believe they were intended to be replaced at certain intervals. The first gen ctis on the m939a2 trucks gave ctis a bad rap.