Hi all !! This weekend I was using my 18j to dig out some ditches. One track went into the ditch and the blade knocked the hyd supply line to the lower ( crank driven) pump off. The deisel started running away for no apparent reason ! It wasn't ingesting hydraulic fluid, but SOMEHOW it was. maybe the "gear pump" was somehow letting fluid into the air intake ?? the engine oil did not rise ?? I dont understand that at all ! I got mad and drug it behind my implement shed, the blade and boom are down and was destroying the ground when I was attempting to move it with the tracks. Got it out, back together, filled with hyd fluid, and now ZERO boom or swing (rotation) operation, the blade dont even move, it seems to be independent of the valve block. The travel and boom swing pedal works fine I checked the pressure from the lower pump, and have over 1500 PSI when activating boom swing pedal. The "gear pump" that bolts to the back of the timing cover has ZERO pressure. Why would that small pump operate the boom,swing, and blade ? :beatsme I have flow with no load, the "block valve" has power and the switch/ relay are turning on and off. I have fused power on 1 wire (brown) and when the switch is turned on, It powers the other wire (why doesn't it ground the other side ? ). does the "gear pump" power these ? I cant find a repair manual ANYWHERE, :Banghead and the parts manual is of little help. Anyone have experience with these ?
one more thing, the engine is an isuzu 3la1. Maybe the whole block is an intake ?? Maybe the small pump opens hydraulic circuits ?
Got it fixed !! The upper (gear pump) plumbs through the "valve block" and activates hydraulic circuitry for the main control hyd block on this unit. I had flow FROM the valve block @ the pressure test port, but ZERO pressure. I pulled the out line off of the gear pump and bled it there, small amount of air came out, put line back on and everything came on line I STILL don't understand the engine runaway :Banghead It's running fine now. The valve cover on this 3la1 isuzu has the air intake built into it with a separate gasket sealed area over the intake "window" that's made into the rocker box sitting on top of the head. I'm thinkin about dropping a kubota unit in to run this thing, They're ANVILS !! just hafta figure a way to run the gear pump. The main crank driven pump wouldn't be that hard. This isuzu engine has been a headache for ALL the previous owners.. rebuilt, head work, and more. NOW I've got compression leaking into the cooling system... overheating is why they sold it to me... after 18,000 in repairs the past 2 years