Having some issues with my otherwise reliable F150 that I'm hoping someone here may be able to help me figure out.

Last week, I replaced the coil pack and spark plugs. There was a CEL on before I did this, but I didn't scan the codes. The truck ran fine for about 2 days before suddenly starting a bad shudder between 1100 and 1900 RPM. Checking codes returned P0171, P0303, and P0316. Replaced the Bosch plugs (first time I had used them) with Motorcraft plugs. Noticed that the plug for cylinder 3 appeared to be fouled, which goes along with the P0303 code. Replacing plugs did not help the shudder issue.

I've since done the following:
Swap the plug wire for cylinder 3 with another one - no change.
Swap the cylinder 3 plug wire position on the coil pack from the bottom to the top - no change.
Spray starting fluid around the intake and vacuum hoses to detect any vacuum leaks - engine idle never changed.

The truck drives like hell at anything more than a light throttle between 1100 and 1900 RPM. Drives much better at 2000 RPM or above, and it seems to idle without much issue.

Any thoughts? I would greatly appreciate it. I want my dependable truck back.

 

Swap an injector with #3 and see what happens.

 

You may have gotten a bad coil, or cracked it while installing it. What brand coil did you buy? It should have a warranty.

You might be able to see if there is an issue by misting the engine bay with a spray bottle. Do it in the dark and take the bulb out of the under hood light-then look for arcing. With the motor running, of course.

 

I considered this, but if this coil pack has a coil that is common to 2 cylinders, if this were a bad coil, wouldn't the misfire code show up for both cylinders that fire from that coil?

I ordered the coil pack from Rock Auto, don't remember the brand. Wish I had kept my old one so that I could swap it back.

 

Nope - I had a cracked coil pack cause a miss in only one cylinder.

I would change all the wires on general principle - Rock Auto has a Motorcraft set at a very good price. You may also want to do a compression test.

 

If the problem was caused by bad wires or bad coils wouldn't that cause a rich condition instead of a lean condition?

 

I removed the coil pack and checked for cracks to make sure there were none, and there wasn't any damage. At that point I was out of patience and took it to my mechanic.

At the shop they did the basic troubleshooting I had already done (swapping wires), with the same results. A compression check showed good compression on that cylinder. Checking the injector with a stethoscope revealed that the injector for that cylinder didn't sound like the others. Replacing that injector fixed the issue.

So I think the gold star goes to Roadie!

 

Thanks!