Does a lean misfire smell like unburnt fuel?

Question

I'm trying to track down a misfire, and it unfortunately wasn't the obvious stuff like plugs or wires. I'm trying to figure out why the misfire is occurring (too much fuel, not enough fuel, not a consistent spark, etc). That will help me know which system to look at more carefully.
Because it's a somewhat old car (17 years), I'm suspecting the fuel filter may be causing issues. If that were the case, I would expect a lean misfire. Would a lean misfire give off the smell of unburnt fuel?

tlhIngan · Answer

There's lots of things that can cause misfires.

If it's an occasional misfire:

fuel pressure: conduct a fuel pressure test. It could be the fuel pump getting weak, the fuel lines being obstructed, the fuel filter being plugged or the fuel pressure regulator not doing it's thing.
spark quality: you said it's not the plugs or wires, check your distributor cap and rotor (if equipped) and your igniter.
airflow: check your air filter, air meter (if equipped) and test for air leaks downstream of your air meter.
compression: perform a compression test, make sure all cylinders are even.

If it's a constant misfire ("dead cylinder"):

identify the dead cylinder: run the engine until the exhaust system gets hot (don't touch it!), then drop a little bit of water on each tube of your exhaust manifold to find the one that doesn't sizzle.
fuel injectors: perform an electrical test on the fuel injector of the affected cylinder.
compression: test the compression of the dead cylinder and compare it to the others.

Does a lean misfire smell like unburnt fuel?

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