What causes cylinder 4 on a Ford V8 Triton to misfire?

Answer 1

Cylinder 4 misfire appears to be a common problem on the Triton V8 especially on trucks. There are several possible causes of misfire ranging from worn spark plug to faulty coils. But that does not address why cylinder 4 seems to be more susceptible to misfire than other cylinders.

Different firing arrangements exist depending on the year. I will address this answer toward '97 model year F-150 trucks that have two separate coil packs, one for each cylinder bank, though most of this answer can be broadly applied.

Check engine light code P304 indicates cylinder 4 misfire. This is a general cylinder misfire indication, not necessarily a component failure many of which, such as the coils, have separate codes. So let's look at some factors:

Cylinder 4 uses one of the longest plug wires on the engine. The longer the wire, typically the higher the resistance. High resistance makes it more difficult for electricity to travel through the wire.

On the F-150 cylinder 4 is inconveniently located underneath the cowling making the plug difficult to reach. It is also positioned right below the heater hose connections.

Spark plug gap recommended on these engines is very wide .054".

This adds up to a cylinder 4 spark that has to fight its way through a long run of high resistance wire to reach a spark plug with a big (huge) gap that it has to jump. By the time the spark reaches the cylinder 4 plug it is tired and just looking for ground.

Add to this the last ingredient and you get misfire. That ingredient is water/oil. This can come from a slight leak in the heater hose connections which is directly above cylinder 4, washing the engine, or a minor oil leak.

The Solution.

Before you spend a dime, remove the spark plug boot. If you see any moisture oil, or water this is most likely the problem. When I say any, I mean any wetness even if it is just a drop. This occurs with surprisingly little amount of moisture present. Remove the spark plug and look for wetness below the hexnut and on the threads. Completely dry the spark plug. Dry the inside and outside of the spark plug boot. If available blow compressed air down into the cylinder 4 plug hole to dry it off. If it is a reoccurring problem reduce the gap on the plug slightly and reinstall all parts.

You will immediately feel the difference if this is the problem.

Happy motoring

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