This is regarding the 5.8L EFI351W in my '95 F-150, but might be a good general 302/351 issue.
I changed spark plugs in the truck at 90K miles, recently. Removed Motorcraft, replaced with Motorcraft. Don't know how long the old plugs were in there, but they didn't look too rough. However, all of them were gapped at .35, whereas the standard for this engine is .42-.46. I gapped all of the new spark plugs at .44.
After doing one fill up of fuel since, I've found that I've lost 3 mpg. 10 mpg dropped to 7 mpg. All in town driving with front hubs locked most of the time. Only other things changed on the truck around the time of the spark plugs were as follows: Bosch O2 sensor, fuel filter, exhaust (removed 2nd converter and installed pipe with turbo muffler), distributor cap and rotor, 9mm plug wires, battery, oil change, belt.
Even with the growly turbo muffler, I don't think that I was driving the truck any more aggressively since the change of parts. I baby this truck like you wouldn't believe. The truck idles and runs smoothly, much better than before. The weather has been nasty cold and the truck does get a fair amount of idle time in, but no more than before.
I'm open to all relevant suggestions on this. Thanks.
I changed spark plugs in the truck at 90K miles, recently. Removed Motorcraft, replaced with Motorcraft. Don't know how long the old plugs were in there, but they didn't look too rough. However, all of them were gapped at .35, whereas the standard for this engine is .42-.46. I gapped all of the new spark plugs at .44.
After doing one fill up of fuel since, I've found that I've lost 3 mpg. 10 mpg dropped to 7 mpg. All in town driving with front hubs locked most of the time. Only other things changed on the truck around the time of the spark plugs were as follows: Bosch O2 sensor, fuel filter, exhaust (removed 2nd converter and installed pipe with turbo muffler), distributor cap and rotor, 9mm plug wires, battery, oil change, belt.
Even with the growly turbo muffler, I don't think that I was driving the truck any more aggressively since the change of parts. I baby this truck like you wouldn't believe. The truck idles and runs smoothly, much better than before. The weather has been nasty cold and the truck does get a fair amount of idle time in, but no more than before.
I'm open to all relevant suggestions on this. Thanks.
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