New spark plugs: misfire at idle.

Did you gap them correctly?

Did your old plugs use spacers? Do your new ones?

Did you overtighten them and crack the porcelin?

Doc

The new set of plugs, both the Bosch and Champions , were gapped and installed correctly. The old plugs are way overgapped due to worn electrodes ( I didn't adjust them).

This is a high milage truck ( 202,000 mi ) . I've also replaced cap, rotor and distributor with no change, old plugs run great , new plugs crappy..

Possibly the older plug with a wider gap is compensating for a lean fuel condition.

You maybe onto something here. Well, no troublecodes have been set so there is little chance of finding this possible lean condition at this time. Do you think an aftermarket ignition upgrade will help, like provide a stronger spark?

What about the plug wires? Open your hood up at night in the dark with the motor running and look close at the wires. If you see a small light show you have your answer.

Bob

Sorry.. I forgot to mention. At the same time plugs were replaced I also replaced, wires ( bosch) , cap , rotor. I've played around with wire routing . Also had to replace distributor because the rusted cap screw broke in the distributor during removal.... very common I've heard.

You may want to check to make sure you placed the wires in the correct firing order. Although you mention with the old plugs it seems to idle better for you, you probably have it right. also check to make sure you are seating the new wire on the plug nice and firmly as well as at the coil side....I would also check to make sure you put the distributor in properly.

good luck...

Fwed

The Ford TFI ignition is capable of supplying a 40KV+ spark, so no, an after-market ignition is not likely to improve matters.

When a cylinder (or cylinders) are starving for fuel, there are not enough fuel molecules in between the spark-plug electrodes to sustain a flame, so the addition a bigger spark does little to improve the driveability fault. The worn spark-plugs obviously have a bigger gap, this allows for more fuel molecules in between the plug electrodes, allowing the flame to be sustained.

That's the theory...

That makes a lot of sense. OK... Lean condition is what we will go with . The old plugs are in and the truck is running good. I suppose the thing to do is widen the gap of the new champions and re-install them... Then I guess we will wait until a) The lean condition gets worse or b) sets a troublecode.

Hi, why don't we just use what we know works. Older cars, burning oil, would fire much better if we used pieces of old inner tubes, punched 2 holes in a flat 1-inch square piece, inserted the sp.plug wire thru one hole, and placed the 2nd hole over the plug end. Holes were spaced just so the spark had to jump an air gap to get between the wire and the plug--imagine the wire never touches the plug; instead, it merely hangs near the plug to force the spark to jump. With your high mileage vehicle, it seems like you have a quite similar condition, be it oil or compression or rich/lean fuel mixture. Do as someone else recommended: widen the gap on the new plugs. Try opening them just a couple of thousandths at each try until you reach that happy gap the engine longs for. (Normal human temperature is 98.6 degrees F. My normal is about 97.0. So, when my body temp. reaches "medical normal", I have a fever!) Also, if original Champions are non-platinum, I'd replace with like plugs; if orig. are plat., then use plat. HTH & good luck. sdlomi2

The motor has 203,000 miles... high milage for certain... but it doesn't use ANY oil between changes. I think this motor has a lot more life left . Could be running lean but no trouble codes are set. The old plugs looked ok in colour, trouble is, I'm not sure what is a "normal" colour plug for this engine. Anyway... The proper gap for this engine is .042. I widened the gap on the new champions to .060 and re-installed them . Everything is running fine now. Of course, the mystery - Why properly gapped plugs would cause the engine to run shitty and grossly overgapped plugs make the engine run great- ... that mystery remains to be solved.

Do the new plugs have the tip extended as far into the combustion chamber as the old ones? I've had one engine that misfired on Autolite plugs, but always ran great on Champion or Motorcraft plugs intended for the SAME application, and the only difference I could ever see was that the design of the Autolite plugs resulted in the tip not being *quite* as deep into the combustion chamber as the other types.

The other possibility is that there's something else wrong in the ignition system causing the spark to be weaker than it should be, and the added length of a slightly bigger gap (maybe) compensates a little. Although my first thought would be that a weaker pulse just wouldn't jump the wider gap at all.

The new plugs are identical to the old plugs ( champion truck plugs ). Like I said, the truck was running great with the old plugs so i dont think this is a plug brand problem. Its running much better now, but still better with the old plugs which were badly worn. I probably need to gap them a little more .

I've seen that alot over the years. Seems the ECM gets used to the wear of the old plugs. Regap the new plugs to factory spec and clean out the IAC. That usually takes care of it.