Hi all! My 1997 Explorer 4.0 is giving me a run for my money. About a month ago, it started misfiring and threw a P0300, 301 and 306. It didn't misfire constantly though only most of the time; sometimes it would run perfect which leads me to believe the issue is electrical. I've had trouble with the coil before so I changed it and no difference. The next time I scanned it, there was only the 306 code. Next I made sure that cylinder six was misfiring and the rest were firing by pulling the wire off the coil. All checked out but one and six. I've already checked the wires, they're both good. I swapped the plug on cylinders 5 and 6 in the hopes that the problem would follow the plug; nope. Fuses are all good. So I know the coil, wires and plugs are good. That leaves me with air and fuel. I can't imagine anything is wrong with the air intake seeing that it still runs. That leaves me with fuel. It has 200k on it and I've never done injectors. Maybe its injectors but why would they only be faulty part of the time? Any pointers would be very, very helpul! Thanks in advance!

 

When you swapped the spark plugs around was the plug from 6 noticeably different in appearance from 5? Was it completely dry? Was it nearly black? Any indication that it's either not getting fuel or not burning fuel?

Injectors are an electrical solenoid with fine grid to atomize fuel. If the solenoid coil has an intermittent connection, the fuel injector could work fine at times and fail at other times. If there is some tiny particle floating around in there, it might block the nozzle at times but be mostly fine other times (this seems pretty unlikely though). At least on other models of Fords from around that time, the injector wiring harnesses had issues. That could always be a possibility as well. You also might want to make sure the locking tab on the injector electrical plug is still present and working as designed. Those become quite brittle over the years in an engine compartment.

-Rod

 

See that's another reason I lean towards a fuel issue.. The two looked exactly the same. A little brown on the porcelain but not carboned up or wet. Not really all that black either since I just put these in maybe 15-20K ago. I've heard from others too that these wiring harnesses are starting to crack and break apart from heating and cooling where they're basically IN the frigin engine. You apparently know much more about the internals of an injector than I. I wondered how an injector can be fine one minute and not the next. It's looking like I'll be doing injectors. Not only will I find out if the connector is broke or not, I'll know if the issue was injectors. It's some process to get to them though! A mechanic friend suggested maybe the wires are leaking some of the current. While I was putting the plug wires back on the coil, a couple of them zapped me right through the plastic end where it clips on to the pack. Highly unlikely but I got my work cut out for me. Thanks for your time Rob.

-Craig S.