x749 Diesel Stalling
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    BDubs's Avatar
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    x749 Diesel Stalling

    Hello - I am grateful for anyone who can help me track down the issue I am having. Here's the background:

    x749 w/ 3cyl Yanmar Diesel @450hrs on it - Was running great for snow duty, aside from the battery being time for replacement. I serviced it last weekend with the following:

    Battery (from Deere), changed oil, oil filter, air filters (inner & outer), fuel filter* and cleaned all the radiator screens, radiator fins etc. I don't think the fuel filter was EVER replaced by PO it disintegrated and end caps fell off)

    *First time changing fuel filter on a diesel - learned my lesson - didn't fill up the bowl and played hell getting it to run and stay running. The Mikuni inline primer DOES NOT WORK on this machine. I can pump hundreds of times and not a single drop of fuel gets transferred to the fuel filter bowl. I wound up filling the bowl, and using a MityVac to suck fuel up to the mechanical pump inlet - there are NO air purge screws on this machine which is nonsense. As I said it took at least 45min of starting and restarting to get it running right. This was last weekend.

    Fast forward to today - put new blades on the 62C deck and started mowing. Did about 2 acres with no problem. Slow, fast whatever - worked as I expected it to. However, after this, it started to die and stalled out (light cutting slow or fast - no difference) - It took about 5 restarts to get it 1000' from where I was mowing back into the shop. I have absolutely NO CLUE where to look. It *seems* to me it is running out of fuel, but why and how? I've used this to mow for years and plow in the winter with no problems...(not that it means anything)

    This model, if the screens get plugged up with grass will overheat. As a result, it will shut down the PTO/mower deck until it cools. Gauge shows that it is running in the normal range, about 1:30 needle position. I am wondering if the sender/sensor is bad? There's plenty of coolant in it & the overflow. Is the defective Mikuni primer pump somehow a restriction in fuel flow all of a sudden? I never used it before and as I said it doesn't work - could the diaphragm have somehow sucked closed enough to be restrictive?

    I don't know...this is all very strange. Thoughts?

    Thanks a bunch!

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    Fozsey's Avatar
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    Quote Originally Posted by BDubs View Post
    Hello - I am grateful for anyone who can help me track down the issue I am having. Here's the background:

    x749 w/ 3cyl Yanmar Diesel @450hrs on it - Was running great for snow duty, aside from the battery being time for replacement. I serviced it last weekend with the following:

    Battery (from Deere), changed oil, oil filter, air filters (inner & outer), fuel filter* and cleaned all the radiator screens, radiator fins etc. I don't think the fuel filter was EVER replaced by PO it disintegrated and end caps fell off)

    *First time changing fuel filter on a diesel - learned my lesson - didn't fill up the bowl and played hell getting it to run and stay running. The Mikuni inline primer DOES NOT WORK on this machine. I can pump hundreds of times and not a single drop of fuel gets transferred to the fuel filter bowl. I wound up filling the bowl, and using a MityVac to suck fuel up to the mechanical pump inlet - there are NO air purge screws on this machine which is nonsense. As I said it took at least 45min of starting and restarting to get it running right. This was last weekend.

    Fast forward to today - put new blades on the 62C deck and started mowing. Did about 2 acres with no problem. Slow, fast whatever - worked as I expected it to. However, after this, it started to die and stalled out (light cutting slow or fast - no difference) - It took about 5 restarts to get it 1000' from where I was mowing back into the shop. I have absolutely NO CLUE where to look. It *seems* to me it is running out of fuel, but why and how? I've used this to mow for years and plow in the winter with no problems...(not that it means anything)

    This model, if the screens get plugged up with grass will overheat. As a result, it will shut down the PTO/mower deck until it cools. Gauge shows that it is running in the normal range, about 1:30 needle position. I am wondering if the sender/sensor is bad? There's plenty of coolant in it & the overflow. Is the defective Mikuni primer pump somehow a restriction in fuel flow all of a sudden? I never used it before and as I said it doesn't work - could the diaphragm have somehow sucked closed enough to be restrictive?

    I don't know...this is all very strange. Thoughts?

    Thanks a bunch!
    You need to check your lift pump to make sure its functioning. The clue here is difficulty priming after filter change. These fuel systems are self priming. I never put fuel in my filter bowl and it starts and runs like I never had it off. Your injection pump is capable of maintaining suction but it isn't good for it. I suspect you have a lift pump that's failing but functioning because they generally won't prime without some lift once you open the system. Verify fuel flow from the pump first and then pressure if you have flow.
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    Wonder if the disintegrated fuel filter sent some chunks into the injection system that may be plugging things up?

    As for starting, I know the pain. I've had to start my x758 twice like that. Once when doing the normal maintenance to change the fuel filter and again not too long after when I realized there was a leak at the filter housing (can't remember whether I lost a gasket or just didn't tighten it enough). Anyway, both times it was a b!tch to start. Mine has the manual primer which does fill the bowl but that still does not help. Took many, many start/die/start/die... cycles to get it to run.

    Rob
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    I would check your fuel filter,if its sucking air then it would cause it run and shut down.Next look in the tank to see if anything is plugging the in take.The other thing is electrical.I had the A1 module go bad on my x595 which would cause power loss going to the solenoid on the injection pump.That solenoid could also be going.
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    Make sure you didnt put the filter in upside down.

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    BDubs's Avatar
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    Filter not in upside down...hole @ top w/o-ring holds it on the stubby inlet pipe. I see no signs of air intrusion/bubbles when running to indicate an air leak @ filter. O-ring in good shape. I lightly greased it to make sure it had a good seal.

    All sediment from filter/bowl - religiously cleaned out. I had to scrub stubborn sediment from bottom of bowl - so I doubt any chunks got by that weren't already down-stream.

    Please tell me more about the lift pump - It doesn't appear to be electric, but I haven't inspected it very closely. How is it actuated in order to pull fuel from the tank and transfer it to the injector pump? I don't want to make any assumptions here - because I thought its main function inline was for priming the system only. Why it isn't electric is beyond me...I think the 455 w/diesel was...Does it work off vacuum? I bet the diaphragm has a hole in it if it isn't working. I didn't see a rebuild kit available but the whole assembly for $147...Jeez...

    I may have to spring for a manual if it proves to be a module or something. It just seems strange & I hate throwing parts at something by guessing.

    Thanks!

    Hmm...Is there a test procedure for checking air leakage @ the filter? @BigBlue - these are supposed to be hand tight, right?
    Last edited by BDubs; 04-20-2018 at 04:43 PM.
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    Quote Originally Posted by BDubs View Post
    Filter not in upside down...hole @ top w/o-ring holds it on the stubby inlet pipe. I see no signs of air intrusion/bubbles when running to indicate an air leak @ filter. O-ring in good shape. I lightly greased it to make sure it had a good seal.

    All sediment from filter/bowl - religiously cleaned out. I had to scrub stubborn sediment from bottom of bowl - so I doubt any chunks got by that weren't already down-stream.

    Please tell me more about the lift pump - It doesn't appear to be electric, but I haven't inspected it very closely. How is it actuated in order to pull fuel from the tank and transfer it to the injector pump? I don't want to make any assumptions here - because I thought its main function inline was for priming the system only. Why it isn't electric is beyond me...I think the 455 w/diesel was...Does it work off vacuum? I bet the diaphragm has a hole in it if it isn't working. I didn't see a rebuild kit available but the whole assembly for $147...Jeez...

    I may have to spring for a manual if it proves to be a module or something. It just seems strange & I hate throwing parts at something by guessing.

    Thanks!

    Hmm...Is there a test procedure for checking air leakage @ the filter? @BigBlue - these are supposed to be hand tight, right?
    Here's your lift pump. AM882462 Its on the side of the injection pump. An air leak anywhere between the pump and the tank will cause issues as will a hole in your pickup tube in the tank. Its mechanical, not electric. I assumed it was electric. I just looked and discovered I got ahead of myself.
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    arlen's Avatar
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    Quote Originally Posted by BDubs View Post
    Filter not in upside down...hole @ top w/o-ring holds it on the stubby inlet pipe. I see no signs of air intrusion/bubbles when running to indicate an air leak @ filter. O-ring in good shape. I lightly greased it to make sure it had a good seal.

    All sediment from filter/bowl - religiously cleaned out. I had to scrub stubborn sediment from bottom of bowl - so I doubt any chunks got by that weren't already down-stream.

    Please tell me more about the lift pump - It doesn't appear to be electric, but I haven't inspected it very closely. How is it actuated in order to pull fuel from the tank and transfer it to the injector pump? I don't want to make any assumptions here - because I thought its main function inline was for priming the system only. Why it isn't electric is beyond me...I think the 455 w/diesel was...Does it work off vacuum? I bet the diaphragm has a hole in it if it isn't working. I didn't see a rebuild kit available but the whole assembly for $147...Jeez...

    I may have to spring for a manual if it proves to be a module or something. It just seems strange & I hate throwing parts at something by guessing.

    Thanks!

    Hmm...Is there a test procedure for checking air leakage @ the filter? @BigBlue - these are supposed to be hand tight, right?
    I can’t imagine your fuel system is much different than my 2006 era x748.
    The mechanical priming lever should fill the bowl in 10-20 pumps...if that.
    Maybe there is an air leak somewhere.
    The lift pump is definitely mechanically driven from the engine.
    When I change filters, and prime by hand, it usually will die once or twice, then everything is fine.
    It seems to me, you may have an obstruction, or an air leak.
    I would start tracing backward from the hand priming pump.
    I wouldn’t try to start it until you can fill the bowl with the hand pump, or you will probably be replacing the starter too
    Btw, I usually use a light hand on a channel lock to remove / tighten the filter.
    Definitely more than hand tight.
    Last edited by arlen; 04-20-2018 at 05:14 PM.
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    BDubs's Avatar
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    Thanks fellas - Yes - functionally identical to an x748 diesel. This is the 1132cc motor. I think this is a 2010 machine. I forget. I just went out there and looked @ the pump. Yes - mechanically driven for sure. I thought that when I did the filter, there'd be some air in the lines and that the pump would finally swallow some fuel and 'catch' when I pressed the lever down - Nope. Even after running it & knowing there's fuel going past it - still no fluid resistance when pressed - so something is up with that.

    Looked on Mikuni's site Rebuild Kits but saw nothing diesel specific, nor did I see any configurations that matches this pump. I can sniff around harder but it looks like I may have to fork over $150 for a new pump, since I've already established it's not functioning properly as a primer and who knows what else is wrong with it. I can't see inside...but - diaphragm pumps all work the same. So...there should be a piston/lifter that follows a cam and that should press on the diaphragm to pump the fuel. The thumb actuator should just emulate that same motion with the engine off - so if it isn't pumping by hand, it probably isn't pumping via the cam - Does that seem like a reasonable deduction?

    For the heck of it with it cold I started it up after snugging the filter with a strap wrench. I saw no air in there - and it started, it didn't sound very authorative getting to top RPM - I engaged the PTO for mower and it shortly after just laid down and died. It started right back up and ran enough to get it back in the shop.

    I'm not saying there isn't an air leak some place - but I don't know how to test for that. I would think that an air leak could also mean a fuel leak and everything is high and dry everywhere.
    Last edited by BDubs; 04-20-2018 at 05:32 PM.
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    xcopterdoc's Avatar
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    I cant remember the last time I saw one of those fuel pumps go bad. One weird thing about the pump primer lever is that if the pump is on the "pump" stroke, the hand lever appears to be inop. Roll the engine over a lil and keep trying.
    The most common issue I see is a clogged fuel pickup in the tank. I would remove the line from pump outlet and crank it to see if you have good flow. If not, remove inlet line, add some fuel hose to go into a fuel can and see if it picks up either cranking or hand pumping. If no pumpy.. Bad pump. If it picks up fuel then you have a clog in the pickup.

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