Bobcat 742 won't stay running

[jdyoung]

I have a bobcat 742 gas engine. I parked it a week ago, running fine aside from a hole in the rad, we got a cold snap and I tried to start it. The engine turns over and runs as long as I am turning the key, the second I let the key off the engine totally dies. It won't stay running unless I am turning the key. Ran fine before it got cold, I'm hoping someone has some thoughts.

Thanks
Jeff

 

[Itsbrian707]

Maybe something behind the key switch? When you let go of the key it kills spark?

 

[craigb93]

Connect a small jumper from the battery side of the starter solenoid to the battery side of the coil. Try again. If it stays running normally you probably need a new key switch.
If it does not run normally, reset the points gap.
-Craigb

 

[craigb93]

Thinking more about it, the weather change could have driven rodents to the warm engine. If they chewed the resistor wire to the coil but failed to damage the 12v starting jumper you could be getting 12v to the coil through that. It is only energized during key turn.
The up thread test will also confirm whether to look for a bad resistor wire.
The resistor wire is built into the harness to deliver 9v. during normal run so don't splice a ceramic resistor onto the end of the old wire if a repair turns out to be needed.

-Craigb

 

[Tango-Charlie]

Good morning from Wisconsin. I too have a 742 that was very temperamental when it was cold out. I too had experienced the same situations in the past. If it was extremely cold outside I'd have to fully choke it and sound like the same symptoms. I even have an engine block heater. Mine has the Mitsubishi engine and it just doesn't really like the cold. I replaced the points, coil, plugs, etc., and it made it better. With the cold hydraulic oil that too didn't help. My cure after everything was to plug in the block heater a good 4 hours before even trying to start it. The other cure when I thought I may have to use it or snow was coming was to move my p/u truck out of the heated garage and move the bobcat in the night before to allow everything to warm up. I found this was also easier on the hydraulics because the oil would be warm too.

I do agree with the other comments that it could be a mouse that chewed through a wire or a bad ignition switch. Jumping it as mentioned, and a volt ohm meter would help chase those circuits down and testing the ignition switch. I've always been looking for MEL 1138A remote switch which plugs into the harness in the engine compartment but I haven't found one yet.

Good luck with it as I love my 742B as its easy to work on.

 

[jdyoung]

Maybe something behind the key switch? When you let go of the key it kills spark?

Spark seems to die instantly when the ignition isn't engaged

 

[jdyoung]

Connect a small jumper from the battery side of the starter solenoid to the battery side of the coil. Try again. If it stays running normally you probably need a new key switch.
If it does not run normally, reset the points gap.
-Craigb

I am going to try this out and see what happens, is it just a wire that runs between those two locations? Then a key turn?

 

[jdyoung]

Thinking more about it, the weather change could have driven rodents to the warm engine. If they chewed the resistor wire to the coil but failed to damage the 12v starting jumper you could be getting 12v to the coil through that. It is only energized during key turn.
The up thread test will also confirm whether to look for a bad resistor wire.
The resistor wire is built into the harness to deliver 9v. during normal run so don't splice a ceramic resistor onto the end of the old wire if a repair turns out to be needed.

-Craigb

I'll try to locate this wire to confirm if it's damaged, I have had rodents inside the machine before

 

[jdyoung]

Good morning from Wisconsin. I too have a 742 that was very temperamental when it was cold out. I too had experienced the same situations in the past. If it was extremely cold outside I'd have to fully choke it and sound like the same symptoms. I even have an engine block heater. Mine has the Mitsubishi engine and it just doesn't really like the cold. I replaced the points, coil, plugs, etc., and it made it better. With the cold hydraulic oil that too didn't help. My cure after everything was to plug in the block heater a good 4 hours before even trying to start it. The other cure when I thought I may have to use it or snow was coming was to move my p/u truck out of the heated garage and move the bobcat in the night before to allow everything to warm up. I found this was also easier on the hydraulics because the oil would be warm too.

I do agree with the other comments that it could be a mouse that chewed through a wire or a bad ignition switch. Jumping it as mentioned, and a volt ohm meter would help chase those circuits down and testing the ignition switch. I've always been looking for MEL 1138A remote switch which plugs into the harness in the engine compartment but I haven't found one yet.

Good luck with it as I love my 742B as its easy to work on.

Thanks for the help, my 742 has always been temperamental with the cold weather, this is the first time it has turned over when turning the ignition and it cutting out when you stop turning the key

 

[reaperman]

If you have the Ford engine like I think that model does. Check the points gap, it should be set at ,025, they are extremely fussy on the engine. It sucks to have engine issues once it gets cold out!!

 

[jdyoung]

If you have the Ford engine like I think that model does. Check the points gap, it should be set at ,025, they are extremely fussy on the engine. It sucks to have engine issues once it gets cold out!!

It is the Ford engine on this one, I'll pull them out and check the gaps, thanks for the info, I'll update you with the progress

 

[Tango-Charlie]

If you have the Ford engine like I think that model does. Check the points gap, it should be set at ,025, they are extremely fussy on the engine. It sucks to have engine issues once it gets cold out!!

The points were even temperamental on my Mitsubishi that's why I went with the Pertronix electric ignition. No more fussing with points and runs smoother.

 

[shane77]

Good morning from Wisconsin. I too have a 742 that was very temperamental when it was cold out. I too had experienced the same situations in the past. If it was extremely cold outside I'd have to fully choke it and sound like the same symptoms. I even have an engine block heater. Mine has the Mitsubishi engine and it just doesn't really like the cold. I replaced the points, coil, plugs, etc., and it made it better. With the cold hydraulic oil that too didn't help. My cure after everything was to plug in the block heater a good 4 hours before even trying to start it. The other cure when I thought I may have to use it or snow was coming was to move my p/u truck out of the heated garage and move the bobcat in the night before to allow everything to warm up. I found this was also easier on the hydraulics because the oil would be warm too.

I do agree with the other comments that it could be a mouse that chewed through a wire or a bad ignition switch. Jumping it as mentioned, and a volt ohm meter would help chase those circuits down and testing the ignition switch. I've always been looking for MEL 1138A remote switch which plugs into the harness in the engine compartment but I haven't found one yet.

Good luck with it as I love my 742B as its easy to work on.

I have a 642 and just leave mine parked in the Garage heated. When I was in my 20s these would get left out side but be plugged in full time. The old ford and mitch. Motor were always cold blooded. Unfortunately I have never experienced this guys issue. It does sound like a switch issue. Just a side note on cold start. Once running give it 30mins b4 doing any work so everything warms up in the winter... these gasser are good machines

 

[spitzair]

From the symptoms you're describing it sounds to me like it's likely the resistor in the ignition circuit that is causing your issues. What they did was install a resistor between the key and the ignition coil to keep voltage a bit lower and not fry the coil. For starting they ran a wire straight from the key (or starter, can't remember off hand for sure which) to the coil to bypass the resistor and give full voltage to the coil for starting. This is why your machine runs while the key is in the start position and dies as soon as you let the key go to the run position. I'll have a look in my manual when I get a chance and see if I can upload the wiring diagram. I have 2 732s which have the same engine and aside from the 732 not having a coolant gauge in the cab they are wired the same. Both my 732s don't have the resistor anymore and I haven't had any problems with ignition coils going bad so I think you can safely do without it...

 

[reaperman]

On a side note. Make sure to keep the u-joint between the engine and hydro pump greased. It's often overlooked because it's not easy to do, or see for that matter. You need to jack the cab up and look/reach behind the seat. There are 3 (I think) zerks close to each other.

 

[brdgbldr]

I have a bobcat 742 gas engine. I parked it a week ago, running fine aside from a hole in the rad, we got a cold snap and I tried to start it. The engine turns over and runs as long as I am turning the key, the second I let the key off the engine totally dies. It won't stay running unless I am turning the key. Ran fine before it got cold, I'm hoping someone has some thoughts.

Thanks
Jeff

Make sure that you didn't accidentally engage the auxiliary detent. This will cause a hydraulic load while trying to start the machine. I've seen operators accidentally engage the detent just getting in and out of a machine.

 

[Dave1234]

From the symptoms you're describing it sounds to me like it's likely the resistor in the ignition circuit that is causing your issues. What they did was install a resistor between the key and the ignition coil to keep voltage a bit lower and not fry the coil. For starting they ran a wire straight from the key (or starter, can't remember off hand for sure which) to the coil to bypass the resistor and give full voltage to the coil for starting. This is why your machine runs while the key is in the start position and dies as soon as you let the key go to the run position. I'll have a look in my manual when I get a chance and see if I can upload the wiring diagram. I have 2 732s which have the same engine and aside from the 732 not having a coolant gauge in the cab they are wired the same. Both my 732s don't have the resistor anymore and I haven't had any problems with ignition coils going bad so I think you can safely do without it...

I concur on this one. If the ballast resistor fails, you will only have power to the coil and thence the points when cranking the engine (there is a small connector on the solenoid with a wire (blue on mine) running to the coil). It is energized only when cranking. You can test for voltage on the end of the ballast resistor most distant to the coil with the key turned to the run position. Power to that point will tell you that the key switch is ok for that function, then look for voltage on the coil side of the resistor to see if the resistor is ok hence passing power through it. If the resistor is bad, you can temporarily put a jumper on it to start and run, but if you run that way long (hours) you will burn your points. The ballast resistor was intended to drop the running voltage to the coil from 12 volts to ~ 6 volts, minimizing arcing when the points opened, where the voltage at the points as they open is actually ~ 100 volts due to the electric field collapsing on both the high voltage side (i.e. to the spark plugs) and the low voltage(i.e. to the points) windings, hence the tendency to arc a little and burn the points . The ballast resistor is a ceramic block about 2" long and 5/8" square mounted near the coil.

 

[jdyoung]

This is great info, the temperature is supposed to get better tomorrow and I'm going to test this, thanks for this

 

[Tango-Charlie]

On a side note. Make sure to keep the u-joint between the engine and hydro pump greased. It's often overlooked because it's not easy to do, or see for that matter. You need to jack the cab up and look/reach behind the seat. There are 3 (I think) zerks close to each other.

Dido, they are very important. I grease them annually and they are a pain to get to. There are three (3) to grease.

 

[spitzair]

Here's a picture of the wiring diagram for the 732 with the Ford engine, as far as I know the only difference is the 742 has a temperature sensor in addition to the temperature switch... either way, the ignition wiring is the same. In the second picture I'm pointing at the resistor in the diagram. Hopefully you've found the issue by now, but if not, hopefully this helps!
Cheers,
Toby