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Can driving for a year with a misfire cause major damage?


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I have an 05 F150 5.4l 4x4. Last year some stole my catalytic converters, since I only carry liability insurance I could not afford to fix this right away and drove for a year with a welded in straight pipe and only the upper O2 sensors. Of course it began to run like crap after a couple of months, with lots of misfires. I recently replaced the cats and installed new O2 sensors (all 4), and while the truck runs much better now #1 cylinder OBD code P0301) is still misfiring under load. My next move is to replace all the spark plugs and the coil pack on the #1 cylinder. My question is could I have done any major damage driving like that for a year?

2 Answers

My next move is to replace all the spark plugs and the coil pack on the #1 cylinder

First you want to take out the spark plug on cylinder 1 and on another accessible cylinder and look at it.


This will help you understand how it was running previously. Here's a link to an explanation on what to look for:

Which is important if the engine won't running properly after the spark plug change.


Next you want to clean the throttle and the sensors, if they're really bad you might need to look at the intake valves.

I wouldn't randomly replace a coil, id replace the plug, I'd drive it 20-30 miles with the new plugs and see how it acts.

Assuming it doesn't take too much labor time to replace the coil. Remember to use OEM/Denso coils.

could I have done any major damage driving like that

The O2 sensors are there to correct the mixture and asses the quality of operation,

Often you see small bad engines get destroyed pistons or oval cylinders from detonation / poor mixture.


So that's not a good thing to do when we are talking about a weak engine like the 5.4 Tirton 3 valve.

But hey as far as the cylinders and pistons it's really not that bad so you might get away with it.


Have you ever had the check engine light flash? That’s when the catalytic converters are being trashed by unburnt fuel. The longer you wait to fix a dead cylinder the more you are risking those new cats. 
 Quick test to see if it’s the plug or the coil just switch coils between 1 and 2. If it follows it’s the coil. If not it could be the plug. If you change the plug have the lisle extraction tool available, on cylinder one with the easy access you can have it out even if it breaks in a few minutes.