My spark plugs in my '93 f150 300 keep burning up causing a missfire under load. When I change the plugs with new Autolite plugs or Motocraft plugs the missfire goes away for a few months then comes back. I drive a lot of miles in this truck (about 600 to 800 per week) and it now has 200,000. I'm getting tired of changing the plugs and the problem seems to be getting worse. Also sometimes the exhaust fumes smell real bad. Is it running too rich? What could cause this? Recently changed the plugs, wires(Motorcraft), distributor cap and rotor. Also in the last year fuel pumps, fuel pressure regulator,fuel filter, water pump, thermostat, upper & lower radiator hoses, coolant temperature sensor and EGR sensor. Also I have performed the restrictor plate modification to the EGR valve. I'm getting problem codes 327 (EGR Valve) and some (automatic)transmission codes (torque converter solenoid) and (excessive slippage converter clutch). The engine also pings under load using 87 octane gas. Does anyone have any suggestions or has anyone had the same or similar problems? I also have a '92 f150 with the same motor (no problems) so I do have the luxury of temporarily swapping parts to diagnose the problem. Any help much appreciated! Thanks.

 

do you have any colour photos of the old plugs for us to view and diagnose?

 

You say the plugs burn up, what do they look like when they come out? Color/wear/deposits/smell etc.?

 

There is not much visible wear on the plugs. They have a brown color but no black. The gap still measures .046. They pretty much still look new. I was told by a friend that a rich running mixture can burn up the plugs pretty fast. The engine starts miss firing just occasionally at first. Then it gets worse & worse over a week or two to the point that it is barely driveable. Changing the plugs fixes the problem temporarily for maybe 2 months then it starts again. The truck doesn't run as well as it did before this problem started back in the spring. It lacks power. Sorry, I have no pictures of the plugs but if it's neccessary I'll take some & post them. Any further help appreciated!

 

Nope. Rich causes black sooty looking plugs usually. Does not cause tip wear, only possible fouling eventually. That they have a brown color sounds fairly normal. Lean running causes plugs to burn up due to the high combustion temps. In those cases, the plug will usually look kind of white coated with possible actual burning of the electrode. The pinging could be due in part to the use of the EGR plate, or the EGR fault. That will increase combustion temps. I don't think the plugs are the real problem, even though changing them seems to help. They just don't sound bad enough to really cause what you describe. Or be the real problem anyway...Your spark may be a bit weak for some reason. You've changed most, but the coil...I wonder about fuel pressure. If it gets low, your exhaust can have a funky smell kind of like when a fuel pump is going bad on a carbed car. You need a fuel pressure gauge you can stick on it when it starts acting up. I'd try to clear up the EGR code if not all of them. I hear tell a bad converter solenoid can cause "bucking" problems. I haven't seen that myself though...Make sure the engine is not carbon infested.
Hows the O2 sensor? If it's 10 years old, I change it. Surely wouldn't hurt anything. The puter can't properly control fuel delivery if its input data is faulty. Garbage in=garbage out... MK

 

With plugs in the condition you describe it sounds like your mixture is OK. The plug gap isn't even changing so they aren't "burning up". It sounds more like you have a weak ignition system that is unable to fire a plug that has seen some erosion of the sharp edges during use. Your coil or module etc may be bad. If you find the problem your mileage and performance should increase dramatically.

A shop with a diagnostic machine like a Sun analyzer could spot the problem quickly. The engine computer is worthless for this type of problem.

 

Well, I hate to do it but I finally broke down and took my truck to the mechanic because I felt I was "stabbing in the dark" changing parts. You guys were right on the money about the weak spark. The mechanic scanned the same trouble codes I did so he kept the truck all day yesterday and diagnosed the coil as the problem. He changed the coil and it appears to have fixed the problem. I drove about 100 miles today and had no problems. It ran better than it has since the spring. Thanks guys for your input. It is much appreciated.