B21 starts, then stops immediately on key release

[eepete]

My B21 has an intermittent problem. When I crank it, it starts up. As soon as I release the starter, it stops. If I keep the starter engaged (have done this for about 2 seconds or so just to see what happens), the engine runs on it's own until I release the key from the start position (and it goes to the run position).

I've got the technical manual, and will hit it tomorrow but thought I'd ask in case someone has had this problem before. In particular, if anyone knows what sorts of problems can stop the engine (hi temperature, other problem) via some electrical means that's where I should 1st focus my attention.

I used it for 4 hours on Saturday, and today it would not start. When I had this before, I wiggled the oil pressure sensor and it was happy, but it seems that the oil pressure sensor can't cut out the engine so I think that was just random luck that it decided to run.

TIA

Pete

 

[BruceWard]

I just had this problem on my B21.

The culprit was the Stop Solenoid part number 17454-60010 .

Initially I discovered that the 5 amp key start fuse in the fuse box on the right hand side under the hood at the firewall was blown. I replaced this fuse and was able to use it some more. The fuse continued to blow every few hours. After a few days the stop solenoid started smoking. When I removed it the black rubber coating at the back was damaged. I replaced the stop solenoid and installed a new fuse. It has worked great since.

I found that a small 1/4 ratchet with a couple of varying length extensions was very helpful in changing the stop solenoid. It is held in place by two bolts, one you can see and another you can not.

 

[BruceWard]

The stop solenoid cuts fuel by default. It is spring loaded to push out the shaft cutting off fuel. I believe that the starter circuit retracts the solenoid when the key is in the start position then the 5 amp key start circuit continues to supply power to keep the solenoid retracted while the engine is running.

If you removed the stop solenoid the engine would run and you would have to manually stop the fuel supply to stop the engine.

 

[lhansman]

I had exactly the same problem with my B21 earlier this year and Bruce has correctly identified the problem. The dealer replaced the stop solenoid and the problem was gone.

 

[eepete]

Thanks for the info. I'll check the wiring, and if that's OK order a new part.

Update: Coil resistance on hold in winding is way high (50K) and wandering around by 10K, so that's the problem. Pull-in coil also seems to be low (.6 ohms), but on high current / brief use coils there is often the expectation of increasing resistance (less current) due to winding heating or there is a mechanical switch that cuts in a dropping resistor on pull in, so hard to tell. So now I have to find the part.

Update 2: I have a new solenoid now. The pull in coil is .39 ohms, and the holding coil (which goes to the small red and black wire on the tractor harness) is 11.6 ohms. This coil resistance data should help "the next time". Now to install the part...

Bruce: Service manual talks about some user applied gasket material when replacing the solenoid. Did you need to do this?

BTW, this is a 1997 with 570 hours on it, should have provided that data in the original post.

I _really_ love this site...

Pete

 

[BruceWard]

Update: Coil resistance on hold in winding is way high (50K) and wandering around by 10K, so that's the problem. Pull-in coil also seems to be low (.6 ohms), but on high current / brief use coils there is often the expectation of increasing resistance (less current) due to winding heating or there is a mechanical switch that cuts in a dropping resistor on pull in, so hard to tell. So now I have to find the part.

Bruce: Service manual talks about some user applied gasket material when replacing the solenoid. Did you need to do this?

Since it was smoking I did not check the resistance on mine.

I did not see any evidence of gasket material on the stop solenoid I removed and I did not use any on the new one. The surfaces mate well and I hope are sufficiently sealed.

Mine is a 2004 with about 1200 hours on it.

 

[eepete]

I'm Golden.

They also had the gasket at the dealer, so I put a new one on. On the old solenoid, as you might suspect from the resistance, the holding coil had failed to an open. Bruce, I'll bet yours failed with a short on the coil somewhere such that it drew right around or just above 5 amps instead of just above an amp. That part dissipating 70 watts would slowly bring it to the "smoke" setting.

I put the old part on the workbench, and put a current limited power supply on the pull in coil. It sucked the supply down to 7.2 V at 20 amps, which is right where it should be for that resistance (.39 ohms). The schematic for the tractor shows a wire from the starter motor to the solenoid, so it's likely something in the starter is limiting the current, otherwise that coil would pull about 35 amps. Whether that's a resistor or a tap of of something such that there is either starter solenoid resistance or motor back EMF is not clear. There must be something otherwise that poor little part would dissipate over 480 watts, which would take it's toll if you cranked the engine for more than a few seconds.

The fun of guessing how stuff works put aside, at least the resistance of a new part is now known which might make it easier for the next person to diagnose this problem.

Thanks sooooo much again to Bruce and lhansman. You guys saved me a hauling fee and repair at the dealer. This is also a good reason for buying the service manual.

Now does anyone know the part number for the valve that can turn off this rain? I've got the area for my tractor shed cleared, but it's too muddy to finish the job. And the project before that is also on hold due to mud.

Pete

 

[GaryInWA]

I found this posting after searching why my B21 wont start all of a sudden and it saved me a ton of time and frustration trying to diagnose why my B21 wouldnt start.

Sure enough my stop solenoid is shot and when I removed it my B21 would start right up so I know its a 100% bad.

Thank you for posting this info, I was sure my injection pump went bad (as no fuel was getting to my injectors) and glad its just a solenoid that only took a minute to pop out plus a new one is in stock at my local Kubota dealer.

 

[unseenthings]

Can anyone tell me the size of the bolts that hold the stop solenoid in? They gave gone misssing between removing the old one and installing the new one. I'm assuming metric. Stealership doesn't list size in part database.
Thanks