Tracking down a pesky misfire…
My good old Ford F150 has been a bit ill lately. I’ve had a persistent but not constant misfire in the #4 cylinder that’s been giving me fits for the last couple months.
Spark plugs and wires have been changed in the recent past, and a local shop even replaced a computer they said was faulty, along with an ignition coil. That seemed to fix the problem for about a week, and then the misfire came back.
So today was truck fix’n day.
Some guys on a Ford F150 forum suggested that I check the heater hoses that carry hot coolant out of the heater core. If those hoses had a leak, it could drip right down onto the #4 spark plug and cause a short in the plug well.
So today I checked that. No drips from the hoses, and considering the temperature outside, the hoses weren’t even perspiring; I wish I could say the same for myself.
As a last ditch effort, I pulled the #4 spark plug out and replaced it with a spare I had sitting on the shelf. Voila that seemed to fix it.
A good test drive down the highway revealed no evidence of a misfire, so I’m slightly relieved. If I can go several days without a problem, I’ll just assume it was a bad plug.
Money Saved?
I vowed that if I couldn’t find the problem today, I’d make an appointment at Ford for a quality diagnosis. I’ve taken the truck to my local mechanic, and while I thought he fixed the problem, it showed back up less than a week later. That was after he spent nearly $700 in parts (the computer, plugs, wires, etc) to fix the problem.
The local Ford dealer will charge me at least $75 for a diagnosis (refundable if I have them do the work to fix the problem) and while I have a high level of confidence they’d find the problem and fix it, it will surely cost me a fortune!
So the fix really cost me about $8 for the spare spark plug I already had, and a half days worth of my time.
Not bad for being a tightwad, do-it-yourselfer…
Perhaps if my current career hits the skids, I could go on to be a mechanic… but only if truck driving school doesn’t work out!
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Truck driving school looks like the bomb. I think I could only pass the intermediate drug usage class or Coke II if you will.
Did your old spark plug look black on the tip?
@MJ
Just remember, all you need is a ‘C’ to pass.
The old spark plug did look black at the tip, but it wasn’t loaded up with carbon like I’ve seen in others. Since it was black, it tells me the mixture wasn’t overly lean, which I guess is a good thing, and since it wasn’t loaded up with carbon it shouldn’t be too rich either.
I do wonder how you test a spark plug. Resistance values maybe?
With the internet’s unlimited resources, chances are if you dont know the answer, someone does