Hi all:

Vehicle: 2001 Ranger Edge 4.0 V6 SOHC

A couple days ago, my ranger started running really rough, CEL came on, and it coded P0303 Cylinder 3 Misfire. Mechanic's diagnostic showed it was either the spark plug or spark plug wire (he said he moved it around and the code followed). I brought the truck home, and replaced all the spark plugs and spark plug wires myself. Got my replacement parts from NAPA: 6 x NGK G Power Platinum (NGK 7159) spark plugs and Mileage Plus Spark Plug Wire Kit (MPW 3349). The replacement seemingly went smooth and the CEL turned off, but now it's got a really rough idle. Like, the whole truck shakes.

Anyone know what might be the culprit? I'm struggling to pin it down since the check engine light isn't coming back on to tell me which cylinder(s) is struggling.

Thanks!
Craig

 

Sounds like you may have accidently pulled one of the small vacuum lines off, this assumes that it runs fine in all other aspects.
Check your firing order again too.
Also don't rule out a faulty new spark plug or wire, or both.

 

Jeff: Thanks for response. I'll dig back in and check for any vacuum lines I might've tugged out. I wasn't real gentle around the vacuum reservoir inside the passenger wheel well, so that's a possibility.

If it is a faulty new spark plug or wire, is there any way to narrow down which one it's on? I drove around some hoping the check engine light would come back on with a new code to tell me which one to check out, but no such luck.

Thanks!
Craig

 

I've never worked on the 4 litres before, but I've read that it's a pain to get at the plugs.

Wait till the truck is fully warmed up (if possible).
Remove one spark plug wire at a time while it's running and note for changes, if you pull the plug wire off the coil pack and the idle stays the same, then you can start with that wire/plug.
If you have an OHM meter it's easy to check the resistance of the plugs, NGK are usually pretty close to 5k ohms.
Wires should be around 10k ohms, not more the 50k.

Keep in mind that if it was a bad plug or wire, you should get a misfire code though.

If you have gone through all the wires, and the idle still is crappy, you may assume that it's not a plug or wire problem.

Be sure and wear some heavy rubber gloves when removing the wires while the truck is running.

 

Got it, thanks Jeff! And you're not kidding about the plugs being a PITA to get to... the engineer at Ford that laid this thing out deserves a swift kick in the ***. I had to do all three on the driver's side purely by feel.

 

I think I read here on the forum somewhere that removing the plastic inner fender-well enables better access. Not too sure though.
And the wheel has to be removed off course...