743 engine won't shut off

[oracle_of_ferndale]

After removing and reinstalling the fuel injection pump, I started the Bobcat. It revs beyond max throttle and does not respond to the throttle lever or the shut off cable. Managed to stall the engine before it blew up. The throttle and shutoff cable are both attached correctly and the appropriate levers on the engine were turning. Seems like something went wrong on the inside. Can anyone suggest what is broken and how to fix it? Thanks.

 

[Dr_doAbit]

Hi, would it be possible that some seal is damaged so that it can suck in air and perhaps with that underpressure some sort of mixture with fuel ?

 

[oracle_of_ferndale]

Hi, would it be possible that some seal is damaged so that it can suck in air and perhaps with that underpressure some sort of mixture with fuel ?

Thanks Dr_doAbit. I suppose that is possible. I don't know enough about this part of the engine for your suggestion to help me.
A few old posts on a kubota forum indicate I might need to have the injection pump rebuilt. Again, I'm not sure why the throttle and shut lever are not working. Can't really get the bobcat on a trailer to take it to a shop. Should I remove the injector pump and take it somewhere to have it tested?

 

[flyerdan]

Thanks Dr_doAbit. I suppose that is possible. I don't know enough about this part of the engine for your suggestion to help me.
A few old posts on a kubota forum indicate I might need to have the injection pump rebuilt. Again, I'm not sure why the throttle and shut lever are not working. Can't really get the bobcat on a trailer to take it to a shop. Should I remove the injector pump and take it somewhere to have it tested?

In the 743 manual it addresses a pin on the control rack that has to engage a fork or it will result in runaway conditions. If you haven't already, grab the 743 book from the manual thread and reference the pics in the injector pump section. Hopefully it's just a simple misalignment.

Why did you have to remove the pump in the first place?

 

[oracle_of_ferndale]

In the 743 manual it addresses a pin on the control rack that has to engage a fork or it will result in runaway conditions. If you haven't already, grab the 743 book from the manual thread and reference the pics in the injector pump section. Hopefully it's just a simple misalignment.

Why did you have to remove the pump in the first place?

Thanks Flyerdan. This looks promising.
I initially removed the pump trying to understand a fuel leak. In hindsight it was not necessary.

 

[oracle_of_ferndale]

In the 743 manual it addresses a pin on the control rack that has to engage a fork or it will result in runaway conditions. If you haven't already, grab the 743 book from the manual thread and reference the pics in the injector pump section. Hopefully it's just a simple misalignment.

Why did you have to remove the pump in the first place?

Thanks again Flyerdan. I found that in the manual and believe I know what to check. I will try it this weekend and report back.

 

[Tazza]

Thanks again Flyerdan. I found that in the manual and believe I know what to check. I will try it this weekend and report back.

Yep, if it's not installed in the fork correctly, it will run flat out, you're lucky you managed to stall it, when it runs away like this, they can self destruct till you either cut the air or fuel supply.

 

[bobcat743b]

Yep, if it's not installed in the fork correctly, it will run flat out, you're lucky you managed to stall it, when it runs away like this, they can self destruct till you either cut the air or fuel supply.

when I was in nam back in 1967 I worked on dozers, such in cam ran bay. we were 3rd echelon mechanics so we were limited on what we could work on. we had one of those big 4 wheel larks that wasn't running right. one guy said he could fix it so he took the fuel injector pump off and worked on it. put it all back together and while several off us was standing by it he told the operator to crank it up. well it cranked and way she went and the way we went. that think sounded like a runaway train. the operator closed the fuel valve when he jumped down about 6 ft to the ground and was right behind us when thar she went. the darn think blew up but there wasn't hardly any oil spill. when the operator asked one of the older fellows how it could happen he said well apparently the guy did something wrong to the pump and when it started it went beyond wide open and although the fuel was shut off it was running so fast I tactually was sucking up the oil in the crankcase and when that ran out it blew up because of no lubrication. I don't know if that's true or not but it always has made a believer out of me when it comes to starting a diesel. whats ironic they could have waited 2/3 days and got a new pump. just seems they were always in a hurry back then. just glad your pump/motor is okay. good luck

 

[buckwill]

when I was in nam back in 1967 I worked on dozers, such in cam ran bay. we were 3rd echelon mechanics so we were limited on what we could work on. we had one of those big 4 wheel larks that wasn't running right. one guy said he could fix it so he took the fuel injector pump off and worked on it. put it all back together and while several off us was standing by it he told the operator to crank it up. well it cranked and way she went and the way we went. that think sounded like a runaway train. the operator closed the fuel valve when he jumped down about 6 ft to the ground and was right behind us when thar she went. the darn think blew up but there wasn't hardly any oil spill. when the operator asked one of the older fellows how it could happen he said well apparently the guy did something wrong to the pump and when it started it went beyond wide open and although the fuel was shut off it was running so fast I tactually was sucking up the oil in the crankcase and when that ran out it blew up because of no lubrication. I don't know if that's true or not but it always has made a believer out of me when it comes to starting a diesel. whats ironic they could have waited 2/3 days and got a new pump. just seems they were always in a hurry back then. just glad your pump/motor is okay. good luck

hey welcome home brother,, i went over in 68 but to china but in an old diesel electric submarine, spyboat, i was involved in a runaway fairbanks morse 10 cylinder opposed crankshaft 38 ND 8 1/8, if i cudn get it shut down they were going to close the hatch on me and let it suck a hard vacuum on the engine room, scary, i threw rags and eventually put a trash can over the ibtake basket, lost a blower seal and was sucking lube oil, and those fairbanks had a lot of that,, on your little yanmar/kubota, there are only 2 ways to get runaway, a blown seal on the turbo or some failure inside the FI pump, look inside the air downstream side of the turbo, that is on the intake side, pull a hose or something, if its dry, the pull ur inj pump and put it in the injection shop, pump repair is lots cheaper than a total engine replacement, ive heard a few detroit diesels run away and they can make just an incredable amount of noise on runaway, if you are anywhere near them when they make that ahWHOOOOO NOISE YOU WILL Forever think you were waaaayyy too close, buck,, pull the hose between your turbo and the intake manifold, if its clean and relatively dry, bite the bullet and take your pump to an inj shop, buck

 

[Tazza]

hey welcome home brother,, i went over in 68 but to china but in an old diesel electric submarine, spyboat, i was involved in a runaway fairbanks morse 10 cylinder opposed crankshaft 38 ND 8 1/8, if i cudn get it shut down they were going to close the hatch on me and let it suck a hard vacuum on the engine room, scary, i threw rags and eventually put a trash can over the ibtake basket, lost a blower seal and was sucking lube oil, and those fairbanks had a lot of that,, on your little yanmar/kubota, there are only 2 ways to get runaway, a blown seal on the turbo or some failure inside the FI pump, look inside the air downstream side of the turbo, that is on the intake side, pull a hose or something, if its dry, the pull ur inj pump and put it in the injection shop, pump repair is lots cheaper than a total engine replacement, ive heard a few detroit diesels run away and they can make just an incredable amount of noise on runaway, if you are anywhere near them when they make that ahWHOOOOO NOISE YOU WILL Forever think you were waaaayyy too close, buck,, pull the hose between your turbo and the intake manifold, if its clean and relatively dry, bite the bullet and take your pump to an inj shop, buck

I have never seen a runaway in real life, but seen it on youtube. It will just suck up engine oil till it runs out and stops.
I have heard stories of wany people have managed to block the air intake to shut it off, they were lucky, others were not.

 

[oracle_of_ferndale]

I have never seen a runaway in real life, but seen it on youtube. It will just suck up engine oil till it runs out and stops.
I have heard stories of wany people have managed to block the air intake to shut it off, they were lucky, others were not.

The pin on the injector rack was stuck behind the fork. I placed it in the correct position. Bobcat now runs as it should. Thanks for the suggestions and the great stories.

 

[bobcat743b]

The pin on the injector rack was stuck behind the fork. I placed it in the correct position. Bobcat now runs as it should. Thanks for the suggestions and the great stories.

there was a fuel shut off valve just outside of the operators door. he said he closed it on the way off the machine. we had no idea but the old time sergeant who rad the pad explained it to us. I was in cam ron bay. whole lot of sand. we had guys who would forget to put the air cleaners back on after service and them old diesels didn't last long but we were in a war zone so another combat loss. hope you never hear that sound. its scary for sure. that's always been one reason I never did like them. I started my hd4 last year. forgot the fuel was wide open when I started it. scared the heck out of me, it was 80 degrees so didn't hurt anything but it sure brought that memory back. those days are memories for sure. glad you found the problem.

 

[tinknal]

I just bought a 743. Just in case it happens to me how did you kill the engine to stop the runaway?

 

[foton]

I just bought a 743. Just in case it happens to me how did you kill the engine to stop the runaway?

block off the air intake with something that will not get sucked into the engine as fast as you can.