1996 John Deere 490e excavator hydraulic problem

Anytime I have one function that works slow I always try to eliminate the cylinder first with a leakage test, then the circuit reliefs next (usually by swapping them with another). Then I would make sure pilot pressure to the arm caps on the control valve are up to spec. Those are the simplest things to check. After that the possibilities on those machine's get quite complicated.

yes, cylinder checks out good. fresh seals will hold a load overnite. circuit reliefs must work because it'll dig. pulls motor down but not to stall. my thought is how does it function with all 5 (ps) unpluged? must have computer bypass or something. I bought from farmer who had been running it like that for years. computers are flashing. auto idle works for every function. modes seem to make a little difference when switched. when I activate stick in or out I hear a wine from main valve. like staved for oil. until bounce or surge the stick. bam speed and power like it should. every once in a while it'll work without surge like main boom up stick out same time or bucket curl. seems odd it could function with all (ps) too both valves behind cab unplugged. made no difference in function of machine. I expected boom to stop as we unplugged switches. I have 24 volts to solenoids. maybe I'll pull cover plate were steel control line for stick goes into main valve.
I very much appreciate anyone's thoughts on this issue. or service manual for this machine john deere 490E.

thanks, Daniel

Dwallace said:

how does it function with all 5 (ps) unpluged?

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It still functions because it uses an angle sensor for pump position and a differential pressure sensor to know when a function is activated. The pressure switches for lack of a better explanation are for fine tuning of the operation.

Dwallace said:

I have 24 volts to solenoids

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You will always have 24 V to the solenoids. The PVC controls the grounding of those solenoids.

At this point if you want to perform your own repairs I highly suggest you have the owner buy you the TM1504 Tech Manual. You won't find any free manuals out there unless somebody out there has one to share.

One other question, does this machine have a controlled lowering device on the boom (see below)?

mg2361 said:

It still functions because it uses an angle sensor for pump position and a differential pressure sensor to know when a function is activated. The pressure switches for lack of a better explanation are for fine tuning of the operation.



You will always have 24 V to the solenoids. The PVC controls the grounding of those solenoids.

At this point if you want to perform your own repairs I highly suggest you have the owner buy you the TM1504 Tech Manual. You won't find any free manuals out there unless somebody out there has one to share.

One other question, does this machine have a controlled lowering device on the boom (see below)?

View attachment 208560

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no sir, hoses from stick cylinder attach too main valve. boom works as it should. did find a broke wire at tank switch but seems this wouldn't cause just one function to act up. I would like to see a diagram of the variable pressure compensator valves. looks like all the steel control lines have to be removed along with most of the lines feeding the boom. to access the cap bank just like to know I'm looking in the right place.
I did drain tank had some water in it. cleaned filter wasn't bad .also pilot filter had some paper element material in it. pilot control has been rebuilt by JD. made no difference.
if any pressure at all is applied to the stick it works. but if you let everything come to a stop with stick hanging down it'll barely move sometimes not at all. rpms make no difference.

What's your serial number? Sounds like you are having an issue with load sense pressure getting to the DP sensor. Maybe backprobe terminal #2 of the DP sensor and measure the voltage with the key on engine off, then with the engine running with the levers in neutral and then with the arm function activated with your issue happening. Then try it with the boom activated to compare. If there is no change in the voltage when the arm is activated then it would confirm the lack of load sense pressure getting to the DP sensor. With the levers in neutral and engine running you should see about 4.5 V. With a lever stroked it should drop.

mg2361 said:

What's your serial number? Sounds like you are having an issue with load sense pressure getting to the DP sensor. Maybe backprobe terminal #2 of the DP sensor and measure the voltage with the key on engine off, then with the engine running with the levers in neutral and then with the arm function activated with your issue happening. Then try it with the boom activated to compare. If there is no change in the voltage when the arm is activated then it would confirm the lack of load sense pressure getting to the DP sensor. With the levers in neutral and engine running you should see about 4.5 V. With a lever stroked it should drop.

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FF490EX026327
Yes sir, that's what it seems like. I also noticed there is another pressure switch on the bottom of that spool( stick in and out ). should there be voltage there as well?
I can hear a valve bypassing when function is activated. until pump is stroked (usually by another function)then arm takes off.
when I drained tank found the screen and mounting rod laying in the bottom of tank. no telling how long it's be there. lots of snot on it. oil very milky. found paper material in the pilot filter. probly from someone washing out main tank filter. worried debris has got into main valve. I'll try the ps voltage test first.
is there anyway to check or test spool under the control lines without removing them? if I were to hook a gauge to the steel line going in. activate function I should see a pressure spike? how much?
thank you very much for helping me with this machine.

Dwallace said:

is there anyway to check or test spool under the control lines without removing them?

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The only way I can think of and it's only a maybe is to tee into the pilot line on the cap and slowly activate the function. If the spool is sticking I would think it would rise gradually then drop when the spool moves from it's stuck position. A spool that is moving will never have a drop, just a gradual rise. Check the DP and post results.

finally ,got a chance to work on the old hoe. unpluged the dp sensor. 3 wires coming to connector. outside wire has 5.1 v
center 0v other outside 0v. machine still operates the same with dp sensor unpluged. machine running made no difference. didn't see drop when activated. should i scrape the wire and test with it pluged in?

Please re-read post #25 and test DP voltage like I asked. You do not want to test with it unplugged. You will need to backprobe (carefully) the wires at the DP connection.

Also, check your arm in pressure switch and your arm cylinder head end pressure sensor for proper operation.

yes, I back probed term 2. found 4.1 -4.4v when activated lever voltage drops. the more pressure against bucket the lower the volt too .6v
except for stick in. volt s drop slightly 3.3v until boom comes to hard stop then volts drop to .6v I can tell pressure builds also.
stick out volts drop a little more 3.1v boom moves a bit faster but both are weak until end of stroke then full pressure.
this must mean poor volts from ps ?

there is also a ps on the bottom of that spool. should it send voltage too dp sensor?

At this point I think you need someone with MPDr to connect to the machine to check the readings of all the sensors and to see if there are any codes.

will the computer flash codes? got to be a way to self diagnose

I read somewhere there is a way to use a jumper wire. get the computer to flash codes?

The reason I recommend an MPDr hook up is because you might have an on/off switch that is not working or a sensor that is not correct but still within parameters, either of which will not trip a code. It is a quick way to eliminate electrical issues and is easier than diving into a hydraulic issue.

If you are looking into the 4 pin diagnostic plug with the lock tab up you short the right side upper and lower terminals together, then turn the key on to get the blink codes. Make sure you are reading the blinks on the PVC and not the engine controller. Report any codes found.

I highly recommend you get the Operation and Test manual TM1504.

what is the correct way too test pilot pressure? connect to steel line at cap? with tee or dead head into gauge. what pressure should I see at that point?
with the back probe test. am I reading voltage coming from (DP) or going too (DP)?
if I'm seeing voltage from sensor. does this indicate poor pilot pressure?
any help is greatly appreciated..

Dwallace said:

what is the correct way too test pilot pressure?

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Test the pilot pressure by "teeing" into the line that goes to the spool for your problem function. The pressure should rise and fall smoothly as you work the lever. Full stroke of the lever you should see 740 - 880 psi.

Dwallace said:

am I reading voltage coming from (DP) or going too (DP)?

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The 5 V supply voltage comes from the PVC and goes to the DP sensor. The DP signal voltage (should be green/white wire) would be voltage coming from the DP sensor going to the PVC. You should see a varying voltage and the voltage should be approximately the same at various points of operation of any function. The movement and load of the function will most likely be different on different functions and therefore different voltages. A dead headed function going over relief, no matter which function, the DP should be reading approximately the same.

If you are having trouble with only one function then the DP is not your problem. I was just trying to use the voltage to try and narrow down the issue. Lets ignore the DP for now.

I mentioned this before, I highly recommend you get the Operation and Test manual TM1504.

mg2361 said:

Test the pilot pressure by "teeing" into the line that goes to the spool for your problem function. The pressure should rise and fall smoothly as you work the lever. Full stroke of the lever you should see 740 - 880 psi.



The 5 V supply voltage comes from the PVC and goes to the DP sensor. The DP signal voltage (should be green/white wire) would be voltage coming from the DP sensor going to the PVC. You should see a varying voltage and the voltage should be approximately the same at various points of operation of any function. The movement and load of the function will most likely be different on different functions and therefore different voltages. A dead headed function going over relief, no matter which function, the DP should be reading approximately the same.

If you are having trouble with only one function then the DP is not your problem. I was just trying to use the voltage to try and narrow down the issue. Lets ignore the DP for now.

I mentioned this before, I highly recommend you get the Operation and Test manual TM1504.

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490e and 790e will drive you nuts. I used to talk to a guy named Ken Hutters at DTAC and he was the smartest engineer they had.He saved my ass many, many times.Those machines were the first computerized machines on the market and were a steep learning curve for us guys that grew up with the old simpler stuff.By now I would assume that the wiring in that thing is toast so your advice to get the manual will save a ton of time and money.

ok, i,ve got poor pilot pressure to the spool 500-550. also checked other spools 900-950. must be a regulator in that system. were to check next?
can i bypass the little block that the cap lines come from?

I swapped pilot lines at cap. problem stayed in same spool.(stick)
are there o rings that can be replaced under that cap? or should I be looking at pressure compensation valve?
I got my pressure reading with tee at cap.
when I swapped lines, stick became boom. and pilot in question operated it perfectly. so I'm purdy sure it's in that main valve.