Hey guys my '99 expy Eddie Bauer 5.4L is still misfiring. I replaced the plugs with some cheaper Autolites platinum plugs (forgot to gap) maybe a month ago and still had a slight misfire only when cold or at idle. It would run down the road just fine. So I replaced the COP boots and springs which cleared it up a little but it is still there. Now is is progressively getting worse, it misfires at idle when cold still, misfire on throttle tip in and pulling away from a stop and sometimes the spark will break up while driving. I'm running Accel COP which have been on my truck since 122k, it just turned 191k today. No CEL so idk which cylinder is misfiring. Typically when I've had a failed COP on this truck in the past it set the CEL and told me which cylinder wasn't firing. That's what kinda leads me to believe I have a bad plug again. Maybe my truck didn't like the cheap Autolite platinums. I usually run the OEM Motorcraft plugs but they were not in stock at the time so thats why I bought the Autolite equivalent. If I change them again I'm thinking about going all out and getting the NGK iridium plugs and make sure I check their gap before putting them in.

So what should I do?

Shane

 

I wasn't getting a misfire code either when the Expo was running like crap last month, until I hosed down the engine compartment. After doing that, a misfire code presented itself and I replaced the coil. Truck runs good now, I have 8 COP's I just got from E-Bay which will get installed soon. Disconnect one COP at a time to try and narrow down the problem.

As far as the plugs, I always check the gap at installation and they were always the right gap from the factory so you should be OK. Motorcraft is my choice of plug on the Ford's.

How is the fuel filter? IAC been cleaned lately?

 

IAC is pretty new and the fuel filter is maybe six months or less old.

The symptoms my truck is having is the same very symptoms that caused me to change the plugs in the first place. I had a vacuum leak on the EGR solenoid and when I pulled the plugs they were covered in a white ash which means they were way hot! I'm wondering if I lucked out and got a bad set of plugs.

I'd rather not spend $200 on another set of Accel COP or what $400 for MSD. I don't trust eBay stuff.

Shane