2000 E-150 5.4 130k miles. Today, all was well and as I pulled away from a drive-thru, I noticed that the engine started running rough. Got on the highway and floored it and it accelerated pretty good but then when I hit cruise at 60, it was bucking bad enough I turned for home to switch vans. When I u-turned I hit it hard again and after levelling off at 60 mph the CEL started flashing. I put the code reader on as it was flashing but it read no code. After about 30-50 sec. the light stopped flashing and stayed off but the engine continued bucking all the way home. I haven't put fuel in it lately or done anything to it recently. Obviously I need to check plugs, wires and the easy stuff but I didn't know the CEL could flash. What could be the cause of a flashing CEL with no code?

 

The flashing meant it was seeing a problem, but it cleared itself up and the light went off. If it's never had plugs, it's time. Sounds like you may have a coil failing. There is one on each plug, so you have no plug wires.

 

Ah, a COP system. I'd have thought that I'd have noticed that when I was replacing the IAC a year ago but obviously I didn't as I see according to my Haynes manual that I do have that system.

 

Yep, the 5.4L's have always had them since 97.

 

I haven't yet dug into it but yesterday I drove it and it had a P0306 misfire on cyl 6 so at least I know where to start now.

 

Yep, second one back on the drivers side. Not too bad in a truck, not sure about a van.

 

Terrible in a van! I thought the spark plug access was bad on my 89 302 E-150. I'm not even sure I can even replace all 8 plugs on this thing. And boy, those plugs are really deep. I had to use both a long and short extension on the ratchet just to reach the plugs. It was really tough getting that #6 coil bolt back in as its a really small metric size and every combination of ratchets, extensions, and u-joint couldn't get me a very good angle on it.

Anyway, I pulled the coil out and check resistance according to the Haynes manual, and the secondary is supposed to be 8-11k ohms. However the #6 was 5.5k so I figured maybe it was bad. Then I took #5 off since it was right there and it measured 5.7k so then I pulled both plugs. While visibly very worn, both had equal wear. So then I swapped both plug and coil #5 with #6. I took it out and it was just as bad. I had to make a trip of about 15 miles so I took it. On the way back it threw a 305 code so it must be either that plug or coil. I should have only switched the coils though. Because those coils aren't cheap (by my standards) I'm going to buy 8 plugs tomorrow and replace at least #5 and #6 and then check it before buying a coil.

 

Put in new plugs in 5 and 6 and it certainly ran better but still missed. I finally bought a COP and put it on the offending misfiring cylinder and it seems to have taken care of it. I'll drive it more tomorrow to check for sure. Thanks LXman for the coil suggestion and about the lack of ignition wires.

 

Glad to help, I hope it works out for ya

 

It is OK now. I moved onto a vibration problem and found I didn't torque the right front spindle nut correctly when I replaced the rotor several weeks ago. Now all I have to do is get the driveshaft balance again and I'll have a smooth ride.