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Thread: CTIS hwy blinks again after 30 seconds

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    Default CTIS hwy blinks again after 30 seconds

    Hello forum.
    I know that there are a lot of CTIS threads, but I didn't found any usefull info, probably because I am blind... Sorry about it

    I have a M1078 with CTIS partially working. I will try to explain what happen:
    - Air tank is full at 120psi
    - CTIS starting to work (hwy blinking)
    - I hear that the tires are inflated (no air leak, but small flapping noise from the quick release valve?)
    - sometimes it is interrupted (due pressure check)
    - goes on for about 5 minutes
    - ctis stops inflating and vents the tubes (the "hiss" in front)
    - ctis hwy light is steady
    - front quick release valve is venting about 10-15 seconds, then stops (like a italian mocca coffee machine )
    - CTIS is doing the 30 second test (blinking again)
    - CTIS starts all cycle again

    What I checked:
    - wheel valves are OK, they do not loose air. I loose the banjo bolts and hear no sound
    - all tire pressure are 90 psi. Probably because of a change of the ECU.
    - pressing another terrain button deflates. I didn't wait to see deflating the tires but both quick release valves are venting...
    - I had a massive air loss in front wheel valve, change the diaphragm and now keeps the air.

    It is normal that after inflating cycle and venting the quick release valve open for 10 seconds?
    Can be that the from QRV have an issue?
    Can be dangerous having 90 psi on a m1078?

    Thanks and regards from Italy

    Christian

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    Colonel 319cssb's Avatar
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    Sounds like a leak in one of the air hoses to the wheel

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    4 Star General Steel Soldiers Vendor Suprman's Avatar
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    Sounds like a hardware issue. If the system fills and is at highway pressure and tben a few seconds later it does a pressure test and thinks you need more pressure. The ecu could be programmed for higher pressure or it could be that high due to
    a fault and the system thinks there is less. The excess coming out the qrv at the end of a cycle would be increased with the higher pressure.

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    If they vent at all, the QR valves should only vent very briefly. When the control valve solenoid on the PCU is released by the processor, it should open fast and quickly vent the air in the system so it passes the QR dump point of 10-15 PSI as fast as possible. If it is not releasing/venting quickly. A slow decrease in pressure past the QR dump point would cause them to open for an extended period untill the pressure finally drops low enough to close the QR’s. So maybe a sticky control valve or a clogged vent pipe? The PCU comtrol valve vents into the lower cover on the PCU that covers the solenoid valve coils. That cover is connected to a hose that connects to the floorboard port and dumps the air outside behind the grill.

    There are max tire inflation pressures specced in the manuals... the tire manufacturers also specify max inflation pressures.

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    4 Star General coachgeo's Avatar
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    Suprman alluded to this....... It could it be possible you have ended up with a MTV CTIS computer? they run up to 85lb I believe so getting by error to 90lb may be in that computers margin of error. If that is the case consider yourself lucky. Is it to high? what is your load? what tire are you running?

    Pull numbers off the ctis unit and report back here with them.
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    @Plasa
    read in the m1078_TM 9-2320-365-20-2 page 2-1856 and on as I mentioned before the TM hints to a air leak.
    http://www.emilitarymanuals.com/pdf/M1078/TM9-2320-365-20-2.pdf
    Screen Shot 2018-11-08 at 8.17.29 PM.jpg

    In my 1089 5 ton MTV I had the problem of the truck not being able to hold the tire pressure, as a result it would recycle all the time trying to get the pressure to 85psi. What fixed it in the end were new wheel valves as the rubber membrane inside was worn and would not hold the tire pressure as regulated.
    Hope this will help you. But most importantly read the TM troubleshooting procedure and follow it. This is how I solved my CTIS issues
    Last edited by 319cssb; 11-08-2018 at 21:31.

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    Hello all!
    Thank you for your infos.

    @coachgo: I have Goodyear MV/T tires, weight is about 19.800 lbs (9000kg).

    I untighten the banjo skrews and seems no wheel is loosing air. But today I will make the soap water test.
    I'm quite sure that the ECU is not original, it was replaced from another truck. I will ask the vendor what truck was, and write down the numbers on the actual ECU.

    The control valve solenoid release quickly, a short and loud hiss. But after that the quick release valve continues to vent for about 10 seconds. Can be that 10 seconds are enough pressure loss that the entire system recycle again? When inflating no air loss on the quick release valve...

    Can be that the pressure sensor on the PCU is faulty and sends wrong pressure to ECU? That can be the source why it's always inflating, and why it's always recycling... Is there a possibility to check it? I have no Y cable so no DDT. Just multimeter....

    Thank you very much for helping me out!

    Christian

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    Hello again.
    I'm now quite sure that the ECU is from a FMTV 5 ton truck. That can explain why the pressure is so high.
    Are the ECU compatible with the original pressure transducer on the PCU? If I change the pressure transducer on the PCU, makes diffrence?
    It's possible to change pressure settings? I read on other threads that settings depends on 2 pins (high, float, ground), but maybe they are set inside the ECU?

    Thank you very much and sorry for all the questions...

    Christian

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    The ECU can be reprogrammed. But on the original (A0) truck it is very difficult. On A1 trucks it can be done with a laptop, the 'Dana diagnostic tool' software and a dearborn adaptor. There you just plug the laptop in change the target tire pressure and save.
    But even if the pressure is too high, it should be able to hold that pressure. I think the secret lies with a faulty valve.


    you could connect shop air to the truck. That way you can energize the ctis without running the engine, which makes spotting air leaks a lot easier
    Last edited by 319cssb; 11-09-2018 at 08:30.

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    Yes, I use shop air to the truck. Today I need to recheck it again. I untighten the banjo skrews, let's see if some tire has diffrent pressure...

    Thank you very much!

    Christian

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