Originally Posted by
skyfox10
Simply put, Autolite & Motorcraft plugs are what your engine should be running.
300/302/460 all take autolite 25's
351 takes 24's.
Also, you will generally have better luck with copper electrodes. I've seen many people have trouble with platinums. I had a set of platinums (AP24) that worked fine until I widened their gap. Once I replaced them with the plain coppers (24), the truck ran great.
Did you change your wires? If not, moving them around to change the plugs could have cracked the old insulation, allowing the spark to leak out. You may find a big decrease in low end torque if this happens, because the spark will jump the gap at the plug easily until you start adding more air/fuel and increasing cylinder pressure. The electricity will always take the path of least resistance and if it finds an easier way, it will take it. Also, you should double check that all you still have the firing order correct.
One other thing is that if the wires got moved, you could be experiencing cross fire, a condition where the magnetic field generated by the current in one wire, will induce a current in another wire. Make sure that your spark plugs wires are not running too close or crossing over each other.
Couldn't agree more. Also, Motorcrafts where
specifically designed for your Ford. (The copper cores are actually designed to fail before piston damage occurs/ Double Plats couldn't if they wanted to. They'll keep going till the pistons toast!)
Re: Double platinums for your truck, other than their anti fowling characteristics (not necessarily a good thing/ masking potential engine problems) & duration between changes (at the expense of poor thermal transfer property's, which contribute to higher combustion chamber temp, knocking on the door of the ping threshold). What's to like? Poor choice for timing advance further than stock, gap stretching or sidegap. They require more resistance to be overcome to initiate spark & produce extra heat when they do.
If you'd mentioned the year that would help. The correct gap for you truck depends on the year. Could be .042-.046 or .052-.056. That falls under "mechanic's error, no fault of the engine or plug!
Then there's the firing sequence & plug wire routing. Also dependent on the year. However whichever of the two possibilities it is, either require there own specific routing method be follow to avoid cross fire. Once again, if I knew the year, I'd post the diagram!!!!!
If you really want to run a double platinum, before I upgraded my ignition system & started side gapping copper cores, AC/Delco Double Platinum Finewire Rapidfires ran great. Mororcraft also came out w/ there own D/P Finewire.