Got an 04 4.0 with a rough idle. It started when I was on the interstate and it seemed to hesitate and went away. The next day after work I had parked it and had it running while gathering my things and it started to idle rough/shaking. Next morning I was hoping it was a fluke and ran fine for about 10min. Got to the end of the road and lost power. Limped it back home. Its throwing a P0351. A Ignition Coil A Primary/Secondary Circuit. The coil and wires are about a couple years old. Dont know about the plugs. Bought a new coil and still does the same thing. Tested the IAC and that reads 9.3. From what I've read the P0351 is for cylinder 1. Would one spark plug be the cause? I have worked on many vehicles over the years and had great luck fixing them, but this has me stumped. Could be over thinking when it could be something easy. Will be putting it in a friends garage tomorrow and spending all day crawling through the whole thing. Any help would be great.

 

Welcome to the forum

Yes, one spark plug could cause the problem

Coil A in the coil pack sparks TWO spark plugs at the same time, 1 and 5
They are hooked up in series
Coil pack wiring looks like this
3 4
2 6
1 5
front

Those are the "matched sets" for balancing the engines rotating mass
3 and 4 are both at TDC at the same time, as are 2 and 6 and then 1 and 5

There are only 3 coils in the coil pack, A, B, and C, each sparks its TWO spark plugs when that "sets" pistons are at TDC

So P0351 means coil A did not do a full discharge of its voltage which means a problem in the coil pack OR in a spark plug wire or spark plug in cylinders 1 or 5

 

Last night I replaced plugs, wires, and coil pack. Started up fine and idled fine. Let it warm up for about 5min and no issues. Drove it down the road and no issues. Today I did the same thing but got on the interstate and ran fine for about the first mile. Then lost power. Could only go about 60. Acting like it wasn't getting fuel. Got off the interstate and took side roads to run my errands and it seemed fine. Got to camp, scanned it and the same P0351 comes up. Still lost on this. I was thinking the PCM. But I read some forums on here and some say EEC-Vs were not notorious for failing but old PCMs were....? At start up, it idles at about 1500 RPMs for a few moments. Then idles down to about 1k-1200 RPMs and then down to 700 RPMs.

 

I’m currently having the same problem. What was the solution to your code P0351 WWboater17?

 

Had to get a used PCM. Ford no longer makes or has any if these. Make sure you have both original keys. If not you'll have to have some made to have it keys work to used PCM. All and all spent about $500.