My 743 is suddenly down on power, fuel filter had 220 hours, was clean, sediment bowl clean as well, changed the filter out to elimate it. Air filter, same hours, was clean also. Linkage is fine, throttle stop is still safety wired from the factory. Currently at 2800 hours. Machine runs fine, just low power. Need the lift pump pressure so I can check it. Machine is going nowhere till I get this sorted out, ain't going to junk a injector pump. Ed
Prob. less that 10 psi.. Those injection pumps are pretty sturdy.. Lift pump would be my 1st place to look to. Hell, they're only 40.00 w/ free shipping.. cant hardly make up a tester for that amount.. Make sure the flow TO the pump is not obstructed.. collapsed/pinched line..
We had a problem with a 743 were there was a restriction in an elbow in or at the fuel tank. Also seem to recall a problem with a cracked suction tube in the tank. Ours had a squeeze bulb in the fuel line like many outboard motor tanks have and when there was a restriction in the line to the tank you could squeeze the bulb but it would not re-expand. As i recall it was located on right side of the machine below where the hoist cylinder mounted and there was a shut off valve there too if my memory serves me right.
My dad had a bobcat with a cracked suction line. Machine ran great , and then suddenly died. Couldn't get it started again even though it had plenty of fuel. A little bit of troubleshooting showed no fuel to filters and a Google search revealed a known problem for these machines.
Suction line was replaced a few years back as was the squeeze bulb. I drained & removed the fuel tank to get the old suction tube out, just to prevent future issues. The squeeze bulb will build pressure to the point you can't squeeze it anymore. Will check the Kubota dealer for pricing on a new lift pump diaphram.....saw ebay pumps for $40 or less, I just question the quality. Thanks for all the help, it's appreciated. Ed
if you suspect the lift pump is bad, try this start the engine, run it up to high idle, start squeezing the primer bulb, if the eng RPM picks back up to full throttle, the pump is bad.
Just put the new pump on and fired it up. Will take it outside tomorrow, see how it turned out. Ed
Don't forget, if your 743 had a manual pull cable for shut down, make sure that pull cable puts the shut down lever fully in RUN position when you press down the knob on the manual shut down control.
Time to bump this....I'll give the short version. Had a mobile mechanic stop today. Ain't a damn thing wrong with the engine. It's in the hydraulic system, something is stuck, building pressure and putting a load on the engine. Thinking it's in the aux. circuit....going to start by putting the grapple on and seeing how it cycles. The drive motors seem to be fine, both sides working equal. Ed
is your RH steering lever pushed, and locked in towards the cab? if so, pop it back into the center postion 40 series machines have mechanical aux hyd control, ZRH steering level pushed to the side towards the cab will lock the aux flow, and yea, the engine wont start
My Dad put a bolt in his RH steering lever to stop it from locking into the Aux. Position on his old 743. It would get bumped to the far right and lock in when people were exiting the machine causing starting issues. Real simple to check and see if that's what the problem is.
Aux lever is free, not locked. 80% of the time my attachment uses the aux circuit.... Ed
Gotcha
Soooo, I'm no closer to figuring this damn thing out. Changed the hyd filter, looked like new inside (225 hours on it) going to stop at the Deere dealer tomorrow, see if they can cut it open. Fluid looked decent, slight amber tint, no shiny stuff. Checked all the linkages tonight, all move freely and return to center. Ed
You stated in a few posts back that you were going to put an attachement on it and see how it cycles, did you ever do that?
Yes, put the 4-1 bucket on, works like it should, just slow. Ed
How about the loader arms and bucket tilt, how well do they work?
You stated earlier that something is putting a load on the engine and you suspect it's the aux circuit. Have you tried making a jumper hose connected to the attachment couplers to allow oil to flow in case the aux spool is awry?
For that matter, if you suspect the aux circuit is causing the problem, make a jumper hose to connect to the attachment couplers and tee a gauge in that jumper. If you get pressure higher than charge pressure to the drive pumps, I can't recall the number, somewhere around 300 psi to take a guess, then you've got a restriction downstream of the main control valve. If the gauge is reading normal charge pump pressure for the drive pumps, then you've got a problem in your main control valve.
I don't think it is the aux. circuit, it had nothing plugged in when the problem started. I will make up the jumper and get a pressure reading, have to start somewhere. I'm like blind man with a bad seeing eye dog on this. Thanks for the help willie, it's appreciated. Ed
Managed to get my hands on a 4" pipe cutter today, crude but effective. Ed
and the results..spotless, no debris at all. Gives me a warm fuzzy feeling. Ed
Did my pressure test, at full throttle, no load I have 350 psi with the aux circuit set on full flow. Ed
I was able to get my grubby hands on a tach tonight, book says 2800rpm, I'm at 2475 no load wide open. Ed
That pressure reading you did, was that with a gauge teed into a jumper hose on the aux circuit?
Yes sir. Ed
Well, that's not the correct place to get a charge pressure reading because you may be seeing restriction at the oil cooler, but 350 psi is high. I recommend checking the drive pump charge pressure. Pop the cab open and on top of the drive pumps you should see a JIC elbow fitting with a pressure switch attached to the fitting. Remove the pressure switch and install a gauge in that port. With oil warm, start engine, correct charge pressure at that port should be 95 to 105 psi
What engine speed? Ed
Book doesn't say, it just says start engine after you connect gauge to that port. I assume it would be oil warm engine at idle, then you could maybe throttle it up and see if it changes, but the spec for charge pressure on that port is 95 - 105 psi. Send me a private conversation. For some reason, yeah as a moderator, I can't start a private conversation with a member. Go figure!
Checked the charge pressure at the pressure switch tonight, warm machine at idle. Looks low to me.... Ed
At this point I think you should send a private conversation with Crewchief888 to get him to view this thread. I'd be curious to get his input on this. It's been years since I've seen or worked on a 743, he might pick up on something I'm missing.
Will do. Ed
i thiink you are confusing charge pressure with main hyd pump pressure. if the machine drives ok, your charge pressure is probably good. if you are concerned about the charge pressure you'll need a 250PSI or 500PSI guage to get an accurate reading. check the pressure at full throttle. easiest way to check the main relief pressure is to plug a gauge into one o the aux quick couplers, at full throttle engage the aux lever and read the pressure. (dead headed is the only way to get the main relief to open) you mentioned previously the aux function was slow as well as the lift/tilt being slow. i'm willing to bet you have a hyd pump going bad, or a blown oring on the main relief valve. off the top of my head i dont know what system relief is set at, (i'm assuming it's in the 2500-2800PSI range) but those pumps only put out 15(or so) GPM when they are new.
My aux circuit had a pressure relief valve added for my 4-1 bucket, I can remove it and test. Thanks Ed