cngford

Hello fellow F150 truck fans , i recently purchased a 2002 5.4L CNG fueled F150 with only 48k miles. It drove great when i test drove it but the guy i bought it from told me that i should change the battery as soon as possible because its not the correct size battery for the truck and he said that the battery sometimes will not provide enough power to activate the chip inside the key. When i took the truck home i noticed the dash going crazy and the speedometer needle going all over the place, the theft light on the dash would flash on and off while i was driving and i noticed the engine sputtering and losing power at times and would not maintain a consistent idle while at a stop light. Anyway the next day i bought the biggest Mastercraft battery at O'Reilly's and the truck ran like a champ that whole day. I thought the problem was fixed and all was good. But the next day i noticed that upon accelerating the engine would sometimes misfire... not all the time... only sometimes, and i noticed that each and every time that it misfired; the theft light on the dash would blink quickly and then disappear. I called the guy that i bought it from and i told him that i changed the battery like he told me to but that now it has a misfire and he told me it could be a coil. I have been reading up on coils and everywhere i read people say that the coils shouldnt cause problems before the 100k mile mark. My truck only has 48k miles should i really replace the coils or could there be another reason my truck is misfiring? I suspect the previous small battery and the dash light going crazy when i first drove it home has something to do with what i am experiencing now after a installed my new battery. I read about resetting the adaptive memory on the PCM system but im not sure how to go about doing that or if that would even fix the issue i am having. Has anyone heard of these symptoms? Any advice or guide in the right direction would be greatly appreciated. I dont want to spend a lot of money changing the coils if the problem is somewhere else. Please help! Thanks in advance!

sdmartin65

Truck is bi fuel, do the issues happen with CNG and gasoline?

cngford

Hi SDMartin, actually its not bi fuel its 100% CNG.

Fordfan2006

huh I thought it had 2 tanks one for natural gas and one for gas

Frank_Ford

You should be throwing a code that will tell you what cylinder is misfiring. Based upon what you have said, I would not conclude that it is a coil. It might be but it could also be a fuel issue. Need more information.