B21 starts, won't keep running

[Yeti]

I have a B21 that's about 20 years old. I know there are lots of threads on this but none of them seem to match my problem. I'm having trouble with the ignition system. It has a dual coil fuel cutoff valve and I get power on the low power coil when I turn the ignition on. When I turn the key to start the engine starts and continues running until I return the key to run.

Then the low power coil loses power. I can't see how that could be a bad ignition switch since there is power before I turn the ignition to start and then return.

Could it be the starter relay or ECM?

 

[North Idaho Wolfman]

Bad switch or bad wiring or bad solenoid!
There is not circuit path to the starter relay or to anything else.
There is no ECM on that model.

Turn on the headlights, if they go out when you take the switch from crank to run, bad switch anything else and look down the line.

 

[Dave_eng]

You first need to establish if your machine has an Operator Presence controller i.e. OPC.
OPC machines have the two internal coils on the stop solenoid connected together as you will see in the image below.

If you do not have the OPC system the sequence to the stop solenoid would be key to start powers the strong pull in coil. Key returns to on power supplied to low power hold coil.
Check fuses carefully.
The seat switch could be involved so check its wiring for signs of damage.
Dave

 

[Dave_eng]

I did a little more research on B21. Some have 2 wire solenoid like the one in the wiring diagram I posted previously. These may be OPC equipped tractors although others may correct me.

The tractor serial number would be equal or greater than 62889.

Tractors without opc have 3 wire shop solenoids. Their serial number would be equal or greater than 50716.

I have marked up the wiring diagram for non opc machines.

I suggest you blow up the above wiring diagram and print it for troubleshooting purposes.
With the 3 wire stop solenoid both internal coils share the same ground and this can mislead you when troubleshooting.

If this is confusing please ask questions.

Dave

 

[Yeti]

Thank you everyone! It looks like the ignition switch has an intermittent open when returning from run to start. Using a meter wasn't showing consistent results but watching the headlights while trying it showed they were on, then start, then off briefly when returning to run, then on again. That allows the fuel cutoff solenoid to cut fuel and then there is not enough from the hold coil to reengage even if there is power there. Thanks again!!!

 

[PoTreeBoy]

I have a B21 that's about 20 years old. I know there are lots of threads on this but none of them seem to match my problem. I'm having trouble with the ignition system. It has a dual coil fuel cutoff valve and I get power on the low power coil when I turn the ignition on. When I turn the key to start the engine starts and continues running until I return the key to run.

Then the low power coil loses power. I can't see how that could be a bad ignition switch since there is power before I turn the ignition to start and then return.

Could it be the starter relay or ECM?

Sounds like the run/hold coil on your solenoid is bad. Pull the solenoid, turn the key on and push the plunger with your finger. If it doesn't stay in, your solenoid is bad.

 

[North Idaho Wolfman]

Sounds like the run/hold coil on your solenoid is bad. Pull the solenoid, turn the key on and push the plunger with your finger. If it doesn't stay in, your solenoid is bad.

Read his last post on his issue.