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980H Pilot Pressure Problems

JakeHarrington

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Oct 5, 2016
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77
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Long Island NY
Hi I have been working on my 980H for a few months now trying to get it right for the spring season. i have asked a few question on here before about it. And I could use some more help.
serial number is JMS03132

Im having problems with the loader controls. They usually work fine but some time they stop working completely and random start again and make it really jerky to load with. usually tapping the brakes a few times get the controls back. turning th command steering often makes me loss the hydraulics.

so over the last months i have replaces all the suction hoses and o rings. double up on each hose clamp. replaces the pilot pump. replaced the lockout solenoid, replaced the brake accumulator priority valve.
nothing has helped besides the pilot pump. that has helped on start up to get brake pressure up immediately when cold.

So now i finally broke out the gauges. I have the pilot test port hooked up and have a nice hose with the gauge set up so i can see it out the windshield and watch it while loading.

pilot pressure gets up to 500psi like its supposed then drops to zero and bounces around all back the fourth pretty much randomly and at all rpms. turning usually makes it drop to zero. and hitting the breaks turns bumps it up usually but sometimes it doesn't. i can post a video of the gauge if it will help.

when you turn the machine of the gauge sits at like 300psi

i tried turning up the pressure regulating valves up buy the pilot test port.. that didn't seems to make a difference.


So any more ideas what to throw at this machine i really can't think of anything else.

all help is greatly appreciated,
Thank you Jake Harrington
 

BigWrench55

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There is a solenoid on the control valve that locks out and implements pilot pressure. That solenoid is controlled by a switch on the armrest with the hydraulic controls. Sounds like you have a wire that is broken and loses contact when you articulate the machine. Someone here with more access to cat information than me can help you better with this.
 

Mobiltech

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Also keep in mind that the pressure in the loader arm lift circuit supplies pilot pressure when the machine is not running so any time the loader arms are off the ground you will have pilot pressure coming through a shuttle valve from that. Try testing with the loader on the ground.
I had a customer with a weak pilot/brake pump that would always leave the loader arms up overnight so on cold startup he would have pilot pressure.
 

JakeHarrington

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Oct 5, 2016
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77
Location
Long Island NY
Mobil tech that makes sense actually i did not know that. Maybe i will keep the arms up for the next few days to ensure no air gets in the system.

and paul i was thinking maybe a bad wire but that wouldnt explain the pilot pressure dropping i dont think. The lock out solenoid is after the pilot test port. So with the lock out on or off the pilot pressure shouldnt change? Im really not familiar with the system so please tell me if im wrong.

Also in with the lock out button on the armrest in the off position so the arms cant move, i cant seem to make the pilot pressure drop low. Stays between like 500-350 driving around turning and stomping on the brakes. Does this help?
 

Nige

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Commenting on your three points in order that you wrote them above.
1. The pressure from the bottom end of the lift cylinders is bled into the pilot system. It's not a case of getting air in, the oil from the lift crcuit is fed into the pilot controls when the bucket is in the air. As MT explained - so that the bucket can still be lowered if the engine ever fails and there is no oil being supplied by the pilot pump.
2. Yes it would. If the signal from the switch goes to "Locked" when the switch in the cab is actually in the "Unlocked" position the first thing that will happen is that the pilot system operation is cut off. That sounds exactly like what's happening to you.
3. Again more confirmation that there is likely something amiss in the signal from the Implement Lockout Switch. Once you have it set to the "Locked" position then whatever might be happening in a wiring harness or connector somewhere will not cause the "lockout switch status" to be constantly changing from Unlocked to Locked and back again as far as the machine electronics are concerned.

I thought I sent you the Electrical Schematic for your machine. If not please let me know. Sounds like you may have some wire tracing to do.

EDIT: I just looked at the Electrical Schematic and the Implement Lockout Switch has both N/O & N/C inputs to the Implement ECM. If either of those inputs goes AWOL = no pilot system. (There may be other inputs into the Implement ECM from that same switch, I didn't check that closely)
 
Last edited:

JakeHarrington

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Oct 5, 2016
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77
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Long Island NY
Nige can you send over that electrical Schematic?

Is there a way i can hot wire or jump out the lock out switch? Atleast for testing purposes? Because i really dont need to lock the arms ever.
Im going to bring my meter out today and see if the lock out signal varies when i turn the machine at all.
 

Nige

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Electrical Schematic sent via PM. You can't hot wire or jump the switch because in the signal side of it there is no power.
There is a "digital signal loop" for want of a better word between the switch and the ECM.
If you locate the switch (Page 17 Grid j-7) it has 3 wires on the top half of it, E918, 953, & E917. If you follow those wires to the ECM you'll find that 953 is a common Digital Return. The schematic shows the Lockout switch in the "Locked" position.
So what the ECM is must see simultaneously is continuity between Pins 15 & 14, and at the same time an open circuit between Pins 15 & 13.
Put the switch in the "Unlocked" position and the contacts reverse. Continuity between Pins 15 & 13, open circuit between Pins 15 & 14.
If for some reason one loop changes state from N/O to N/C or vice versa and the other one does not, the ECM will default to the non-operational state for whatever is the circuit controlled by that switch.
My opinion is that this circuit cannot be tested by opening up connectors, it would have to be "back probed" usging spoon-type ends on a DMM.
Having said that it might be well worth your while to open up every major harness connector between the Lockout Switch and the ECM, clean them, and check for corrosion.

upload_2020-3-26_15-0-12.png
upload_2020-3-26_15-3-2.png
 

JakeHarrington

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Oct 5, 2016
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Long Island NY
Figured it out. I switched the primary and secondary pilot pressure regulators with each other and its fixed.. kinda drifts a ton but once i get the new primary and put the secondary back where it belongs i should be up and running
 

JakeHarrington

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Long Island NY
Ok turns out thats not the problem. With both primary and secondary reg valves replaced the symptoms were just as bad as originally. with the two new valves switched and in the wrong position it was ok except for when the bucket was on the ground. With the buck on the floor pilot pressure would drop to zero....
Then the tilt stopping working today. Then started to work again .. now everything has stopped working. No loader arm functions at all.
Plugged it into cat ET again.. still no codes and all the tilt/ lift lever respond and send amperage to the solenoids.

also all 4 tilt/ lift solenoids have been replaced at on this machine at somepoint as i can tell by the paint..

Shuttle and sequence valve are on order of Monday morning. Hopefully with every valve in the pilot assembly replaced nothing else can go wrong
 

Cmark

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If I can just throw this in from the sidelines; On top of the pilot section of the MCV there are two screens, highlighted 59 in the picture. I've only ever seen them get blocked following a major failure or someone getting careless about cleanliness when changing hoses, but when they do get blocked the reduction in flow can cause weird problems.

valve.jpg
 

JakeHarrington

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Long Island NY
I havent calibrated anything in about 2 months. I did it when i first bought the machine to when i replaced the tilt sensor

i will check those screens this morning also. I havent touched them yet
 

Nige

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Based on Cmark's info above I'd suggest to look at those screens as a first step.

Because you changed the regulating valves you should really do a recalibration of the all the main control valve operating functions, but that would be after you've been into the screens not before.
 

JakeHarrington

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Long Island NY
Does anyone know what the shuttle valve and the sequence valve? And how they operate?


Also im only getting 3.4volts to the lock out solenoid. Shouldnt that be 24v? Or is it a lower voltage from from ecm
 

Nige

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Sent you a PM with docs regarding the valves.

Have you tested the coil resistance.? Spec is 32.6 +/- 1.6 ohms.
Are you testing voltage with the solenoid disconnected from the machine harness or are you back-probing it with everything hooked up.?

This is what the SysOp says ............
"The solenoid valve (hydraulic lockout) is an output of the implement ECM. The solenoid valve will disable the pilot hydraulics in failure mode. The solenoid valve (hydraulic lockout) will enable the pilot hydraulics when the solenoid valve is energized by current from the implement ECM. The solenoid valve has a 2-pin connector. One contact receives power from connector contact J1-8 of the implement ECM. The other contact joins together with the other solenoid valves and returns to connector contact J1-7 and J2-3 of the implement ECM. Pin J1-40 supplies power to pin J1-8 within the implement ECM. If the input to J1-40 does not have battery voltage then the solenoid valve will not be energized."

I suggest that you go looking on ECM Connector J1, Pin 40 for battery voltage (to machine frame ground).
Then test the voltage between Pins 7 & 8 of Connector J1 with the machine electrics energized, engine running at Low Idle, and the Implement Lockout Switch in the Unlocked position.
 

JakeHarrington

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Thank you that pin information is exactly what i was looking for. I will do that today.
And when i was testing the volt to the lock out solenoid i was doing it with the harness disconnected
 

Nige

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You need to be testing with the electrical connectors in place, not disconnected, unless the testing procedure specifically states otherwise.

Try to get hold of a pair of “spoons” for the ends of your DMM leads. From memory the Cat Part Number is 7X-1710 for the pair, or 1708/1709 for individual red/black leads. They won’t be cheap, even if you go aftermarket.
 

JakeHarrington

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I ohmed out the h717 and h716 wire to from the ecm connector to the lock solenoid plug. All was well. 27ish bolts goin to pin 40 and pin 1 and pin 2 was a good ground as well at the ecm plug.

Had a friend come over with a set of spoons and he stuck them in the ecm plug at pins 7 and 8 for the lock out circuit and we got 2.4 volts. According to SIS we needed 2.5 volts give or take.

so that all tested fine. And still no movement. My friend had a set of 4 new pilot position solenoid so we swapped one out and the dump started to work the. Swapped the rest and they all worked.
Now the bucket and arms move again. But the pilot pressure is still jumping around everywhere. Basically im back to exactly where i started.
 

JakeHarrington

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Long Island NY
When we back probed it with the connector at the solenoid both plugged in and unplugged it read 2.4-5 so that could definitely be my problem then.
But my question is after all this i ran a hot and ground from the start direct to solenoid so with the engine running like 27 volts and still no difference. So can i rule that out or not yet?

also what do you think can be causing my low voltage between 7and 8?
 
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