L3301 misfire on startup

marksmand · Jun 17, 2025

The last 2 times I started my l3301 I got a bang(backfire?). This only happens when
the tractor had not been used for several days. Otherwise it runs and operates perfectly.
It's not especially hot or cold here lately(50's 60's) but it's very damp. 2014 model with 630HRS
that has been well maintained. Any thoughts?

JWR · Jun 17, 2025

Not had that happen. I would think that (by your description, only after it has sat for a few days) there is a slow accumulation of unburned fuel in your exhaust that gets ignited when you start the engine. Sort of has to be the case (?) But that puzzles me. Diesels only work because the fuel air mixture is compressed beyond it's temperature of ignition. Diesel exhaust is typically rather cool compared to gas engines...and besides that a 'backfire' is usually an instantaneous explosion in the exhaust system... Hmmm ? Exhaust flow, once the engine is running, would shove any unburned fuel rather quickly out of the exhaust pipe and muffler. That and the fact that diesel fuel is not as volatile as gasoline. Come to think of it, I have never heard of a diesel backfiring ! I could speculate that a leaky injector would drip some fuel into a cylinder more and more as it sits there but that would require high pressure out of the injection pump... very puzzling.

tradosaurus · Jun 18, 2025

marksmand said:
The last 2 times I started my l3301 I got a bang(backfire?). This only happens when
the tractor had not been used for several days. Otherwise it runs and operates perfectly.
It's not especially hot or cold here lately(50's 60's) but it's very damp. 2014 model with 630HRS
that has been well maintained. Any thoughts?

I would make a cursory check under the hood to make sure no mouse or birds nest have been created. Pull out the air filter and check. Clean the screen. Any visible leaks around the engine?