Recently, my 110 (19J) has decided to keep running after I turn the ignition off. Even cutting the battery (I have a switch to do so) doesn't do it; only intentionally stalling the engine will work. Is this typically something in the ignition wiring / ignition itself? The problem is inconsistent, so I'm not totally sure where to start looking.
Truck continues to run after ignition set to "off"
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What year vehicle? There are a few likely problems.
1) The fuel solenoid is sticking open. To test, pull the wire off and see if the engine stops. If not, then you should pull the solenoid and look for contamination causing it to stick. You might need a new one.
2) The alternator is back feeding enough power to keep the solenoid engaged. This can happen in earlier trucks via the charge light as they don't have a diode to prevent it happening. Having any accessories on like the heater fan should stop the issue.
3) The ignition switch is not turning off power. Not uncommon.
NEVER disconnect or isolate the battery with the engine running. The alternator is still supplying power and without a battery, it can't control the voltage and this can fry a lot of electrical items. Proper emergency disconnect switches need to have the alternator power running through them on a second contact.
1) The fuel solenoid is sticking open. To test, pull the wire off and see if the engine stops. If not, then you should pull the solenoid and look for contamination causing it to stick. You might need a new one.
2) The alternator is back feeding enough power to keep the solenoid engaged. This can happen in earlier trucks via the charge light as they don't have a diode to prevent it happening. Having any accessories on like the heater fan should stop the issue.
3) The ignition switch is not turning off power. Not uncommon.
NEVER disconnect or isolate the battery with the engine running. The alternator is still supplying power and without a battery, it can't control the voltage and this can fry a lot of electrical items. Proper emergency disconnect switches need to have the alternator power running through them on a second contact.
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I had a similar issue sometime ago, it Turned out to be a defective boost diaphragm in the injection pump, it would occur after driving hard on highway. Fuel would leak into intake chamber and it would lead to a run away idle, where engine would idle until the puddle in the intake chamber would not provide enough fuel but only at idle. If revved with ignition off it would shut down, or idle for a few minutes. Eventually a pump overhaul took care of it.
Thanks all. Keeping my fingers crossed that the fuel solenoid is the issue, as that seems like the most straightforward diagnosis/fix. I have been worried its a runaway idle. I guess if worse comes to worse, I have a new-to-me 200TDI coming in that I was going to swap in, so this might accelerate that project.
1988. And @Red90, thanks for the info about disconnecting the battery. Definitely a desperation move at the time, and one I'll not do again.
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