Sorry if I'm beating a rented mule here. So here we go... Other night I was leaving for work, truck (98 F150 4x4 5.4 168k) statred acting like it was starving for fuel lack of power, shuddering,shaking, clicked off the OD and it acted better at higher RPM's. After a few miles CEL started flashing (never acted up before, sat for three days and it was raining) drove carefully into work where I hooked up a scan tool and pulled two codes P0304 and P1309. I took to a local mechanic and he recommended a tune up and maybe new COP. He did that(8 new plugs, new COP on #4) and also found a vacuum leak (rubber elbow) by #4. He didn't get a chance to drive it, but he cleared the codes and couldn't get any codes. Picked up my truck tonight, at first it ran good, but started actly like a misfire after a mile or two. I notice a 200-300 RPM drop and then recovers. It ran good in low gears and seems to be starved for fuel again in fourth (AOD) better if OD is off and seemed to maintain (no miss) between 55-60 mph OD off. Seems coolant leak in area of #4 is common, but how soon would a leak fry new COP? Wife was following me and said she smelled gas at first but then it got better as we went. I had the CEL on for about 45 seconds (flashing) then went out and stayed off. Any ideas?

 

I just went through this.... check the heater hose clamp (only one you can tighten) above #4. I tightened mine 4 turns(!) Just run you hand down the hoses, towards the clamps you'll find it.

 

Yes, coolant dripping on the COP can definitely fry the COP although I don't know how quickly it can happen.

Another thing that can happen here is the coolant gets down into the plug well. If the plug boot didn't get dielectric grease, then it can get up under the boot and short out the plug and crack the plug insulator, wrecking the plug. Good luck!

 

My FOMOCO plug wires have vents at the top and can drain down to the plug and can short/fry it out as well. My gap on that plug was .05' off, and it casue a CEL to blink, secondary ignition issue!! Regapped and installed, works fine.