New M1089 FMTV owner

[Suprman]

Two different issues. You can jump the pressure switch on the side of the air tank with a paperclip. Could be a bad ecu. They go bad all the time. Easiest way to diag that is swap a known good one in.

 

[319cssb]

Two different issues. You can jump the pressure switch on the side of the air tank with a paperclip. Could be a bad ecu. They go bad all the time. Easiest way to diag that is swap a known good one in.

That's what I've done replaced with a known good one. I've bypassed the pressure switch before with no result
will try again

 

[Suprman]

Bad or unplugged transducer. Drop the passenger kick panel and look at the manifold. See if anything visible going on.

 

[319cssb]

Bad or unplugged transducer. Drop the passenger kick panel and look at the manifold. See if anything visible going on.

I posted earlier that the connector on the manifold has a tightened collar but the rear part of the plug is loosely moving left and right. That didn't seem to be normal to me. I think the entire plug should be solid when it's tightened on the plug

 

[Suprman]

Take it apart and investigate. If there is a short or bad connection somewhere you will get a fault. But it shouldn’t affect data communication with the diag.

 

[wandering neurons]

That connector you've pictured is for your PCU solenoids. Test by disconnecting the plug from the ECU. Test resistance between plug (not ECU) pins B to ground, C to ground, and R to ground, then B to C, B to R, and C to R. You should get around 60 Ohms when measuring pin to ground, and around 120 Ohms when going pin-to-pin. That'll test the wiring from the ECU canon plug through the harness, through your pictured plug, and through the solenoids to ground and for shorts in the wiring. If you get 0 Ohms you've got a short between wires . High resistance could be a bad wire but more likely a bad solenoid.
The other wire on the PCU is for the pressure transducer. There's no feasible way to test that other than check wiring between the ECU cannon plug to the plug on the transducer, and to check for proper voltage at the pressure transducer plug when the ECU is connected and the truck powered on (but not running). Spicer's manual has some good troubleshooting tips. I've concatenated some tests by testing the whole length of wiring.
I had a bad PCU pressure transducer that I found by replacing with another unit. When I powered my truck on, even before building air pressure. The HWY light would flash twice then all five flash from that point on.

I posted earlier that the connector on the manifold has a tightened collar but the rear part of the plug is loosely moving left and right. That didn't seem to be normal to me. I think the entire plug should be solid when it's tightened on the plug

 

[319cssb]

That connector you've pictured is for your PCU solenoids. Test by disconnecting the plug from the ECU. Test resistance between plug (not ECU) pins B to ground, C to ground, and R to ground, then B to C, B to R, and C to R. You should get around 60 Ohms when measuring pin to ground, and around 120 Ohms when going pin-to-pin. That'll test the wiring from the ECU canon plug through the harness, through your pictured plug, and through the solenoids to ground and for shorts in the wiring. If you get 0 Ohms you've got a short between wires . High resistance could be a bad wire but more likely a bad solenoid.
The other wire on the PCU is for the pressure transducer. There's no feasible way to test that other than check wiring between the ECU cannon plug to the plug on the transducer, and to check for proper voltage at the pressure transducer plug when the ECU is connected and the truck powered on (but not running). Spicer's manual has some good troubleshooting tips. I've concatenated some tests by testing the whole length of wiring.
I had a bad PCU pressure transducer that I found by replacing with another unit. When I powered my truck on, even before building air pressure. The HWY light would flash twice then all five flash from that point on.

That's exactly what mine does. two flashes then all 5. whether there is air in the tank or not. or full pressure. Same thing with the other good ECU. I'll grab my fluke 87 tomorrow and do some checking.
thx wandering neurons

 

[wandering neurons]

I still need to to take my kick panel down and read the numbers from my pressure transducer. And there's no way to test the transducer itself.
Funny thing, the PCU hangs "upside down" in the LMTV, which I think causes moisture and crud to get into the transducer. My old transducer was all cruddy inside, the replacement, though used, much cleaner.

That's exactly what mine does. two flashes then all 5. whether there is air in the tank or not. or full pressure. Same thing with the other good ECU. I'll grab my fluke 87 tomorrow and do some checking.
thx wandering neurons

 

[319cssb]

All the pins on the cannon plug check out b, c and r to ground = ~60ohm
all cross connections b to c, b to r and c to r =~ 120 ohm

taht leaves a bad pcu pressure transducer? How do I check for that again?

im getting 4.75V at the transducer plug.

 

[Suprman]

You could take it off and make sure no gunk on the end. Blow it out with air. Make sure you have good air feed flow to the valve body. I dont know the measurements to take on it. I usually use the swap it out method.

 

[319cssb]

So if I understand the principle of operation of this transducer correctly it should be open in ambient air and closed under pressure, correct?
I sprayed it with some stuffs and let it sit upside down for a while and then reinstall and see what happens.

 

[wandering neurons]

According to Spicer's TFM:
"Check for continuity between PCU connector pin A and ECU harness connector J, PCU pin B and ECU pin b (lower case), and PCU pin C and ECU pin c (lower case). Also, check for short circuits in the PCU harness pins A to B, B to C, and C to A".

Later in the test you look for PCU pin B to show between 4.9 and 5.1 volts. You did that and got a slightly low voltage. That voltage is coming from the ECU. Could be corrosion somewhere causing low voltage. That should show up in the test at the top, between pins B and b - do your measurement carefully to see if there's any resistance, and compare with the other two pin pairs. There's notes somewhere on this site about using an eraser to clean the plugs, or just use contact cleaner judiciously...

There aren't any other test for the pressure transducer that I can find.

This afternoon after work, barring any rain, I'll pull my kick panel and see if I can read the numbers on my pressure transducer and post the results.

Everything else either requires a working diagnostic tool or a spare PCU pressure transducer/ECU, and you've eliminated the ECU.

Like Suprman says, the pressure transducer could have crud on the inside blocking it, mine did. But even after cleaning it, mine still didn't work right. I think that the water and crud corroded the sensor itself. But try anyway, it won't cost much other than a few minutes and could "hopefully" fix the problem.

All the pins on the cannon plug check out b, c and r to ground = ~60ohm
all cross connections b to c, b to r and c to r =~ 120 ohm

taht leaves a bad pcu pressure transducer? How do I check for that again?

im getting 4.75V at the transducer plug.

 

[Suprman]

Its a variable resistance sender.

 

[wandering neurons]

The pressure transducer is not a simple switch, it translates the actual air pressure to a voltage. But you can't test it without some specialized equipment - think pressure vs. voltage curves, charts, a test cell. Or the LMTV electronic test tools, if you are so lucky.
This is how the CTIS "knows" what pressures are being sent to the tires. Other than the switch outside the wet tank, this is the only other electrical sensor that I know of in the system.

So if I understand the principle of operation of this transducer correctly it should be open in ambient air and closed under pressure, correct?
I sprayed it with some stuffs and let it sit upside down for a while and then reinstall and see what happens.

 

[wandering neurons]

Jinx...

Its a variable resistance sender.

 

[319cssb]

I have to apologize. apparently I was lying , what I've been messing with was the pressure sender of the wet tank and not the pressure transducer. That one is found on the valve body on the passenger side.

 

[319cssb]

Well, I was able to establish a couple of things:
-the air pressure goes up to 120PSI
-the air dryer purges moisture from the center as it should.
-wḣen I dump the air there is a bunch of moisture and then Ice flying from the purge valves.
-the solenoid block likely doesn't have a stuck valve (i looked)
-the solenoid block has the solenoids installed in the proper way
-the solenoids don't appear to be shortened
-there is pressure at the supply of the solenoid block
-there is no pressure at the outlet of the solenoid block
-bypassing the pressure switch has no result
-switching the CTIS ECU has no result

I'll have to get a pressure transducer

 

[319cssb]

According to Spicer's TFM:
"Check for continuity between PCU connector pin A and ECU harness connector J, PCU pin B and ECU pin b (lower case), and PCU pin C and ECU pin c (lower case). Also, check for short circuits in the PCU harness pins A to B, B to C, and C to A".

Later in the test you look for PCU pin B to show between 4.9 and 5.1 volts. You did that and got a slightly low voltage. That voltage is coming from the ECU. Could be corrosion somewhere causing low voltage. That should show up in the test at the top, between pins B and b - do your measurement carefully to see if there's any resistance, and compare with the other two pin pairs. There's notes somewhere on this site about using an eraser to clean the plugs, or just use contact cleaner judiciously...

There aren't any other test for the pressure transducer that I can find.

This afternoon after work, barring any rain, I'll pull my kick panel and see if I can read the numbers on my pressure transducer and post the results.

Everything else either requires a working diagnostic tool or a spare PCU pressure transducer/ECU, and you've eliminated the ECU.

Like Suprman says, the pressure transducer could have crud on the inside blocking it, mine did. But even after cleaning it, mine still didn't work right. I think that the water and crud corroded the sensor itself. But try anyway, it won't cost much other than a few minutes and could "hopefully" fix the problem.

Actually I got the slightly low voltage on the pressure switch by the tank. At the pressure sensor by the valve block I got over 5V , which is normal according to the troubleshooting guide.
I do have a working diagnostic tool. But nothing to respond to it.
The ECU pin J to Pressure transducer connector A is good. No short to ground or broken connection.
I have taken the pressure Transducer and dropped it in my ultrasonic cleaner. Maybe that's going to do something inspiring.

 

[wandering neurons]

If you're not getting +120 psi, you may not get the pressure switch to close. The screw on the compressor turns counter-clockwise to increase pressure. But bypassing the pressure switch should fool the ECU into continuing, unless something else like the transducer is whacked.

The pressure transducer that I have is Spicer Dana part number 676505, which crosses to NSN 6695-01-509-9496

You might be able to get it directly from Spicer or through a truck repair shop...

I'd be interested to see what the cleaner does for the part!

Actually I got the slightly low voltage on the pressure switch by the tank. At the pressure sensor by the valve block I got over 5V , which is normal according to the troubleshooting guide.
I do have a working diagnostic tool. But nothing to respond to it.
The ECU pin J to Pressure transducer connector A is good. No short to ground or broken connection.
I have taken the pressure Transducer and dropped it in my ultrasonic cleaner. Maybe that's going to do something inspiring.

 

[319cssb]

If you're not getting +120 psi, you may not get the pressure switch to close. The screw on the compressor turns counter-clockwise to increase pressure. But bypassing the pressure switch should fool the ECU into continuing, unless something else like the transducer is whacked.

The pressure transducer that I have is Spicer Dana part number 676505, which crosses to NSN 6695-01-509-9496

You might be able to get it directly from Spicer or through a truck repair shop...

I'd be interested to see what the cleaner does for the part!

i think the issue might be the solenoid block itself.
anyone got one for sale?
i took off the exhaust hose and there is a faint amount of air coming out.
the solenoid clicks, but there isn't much air coming through