Pesky, persistent misfire

[Regular Guy]

Hi all;

I'm getting P0305 & P0316 codes.

I replaced plugs, wires and coil pack and ran some fuel injector cleaner about a month ago, which cleared it up until yesterday.

After a 100 mile road trip, idle became rough and the CEL popped back on.

What's next? I was thinking Crankshaft Positioning Sensor; am I on the right track?

'03 Ranger Edge 2wd
3.0l
129k miles

Thanks!

 

[john93rangerstx]

check for intake leak

 

[RonD]

CKP(crank position) sensor wouldn't cause that.
CPS(cam position sensor) might but it would not be cylinder specific, i.e. 0305

There was a TSB for the 2004-2006 Ranger 3.0ls if yours was a late 2003 then it could apply.
http://ww2.justanswer.com/uploads/jmcdo28/2010-01-20_024443_tsb05-26-03.pdf

New plugs might have cleared it up for awhile.
Compression test on #4, #5, #6 might be best just to take the valve seat issue off the table.

Did you have a look at the old #5 spark plug when replacing them?
I would look at #5 now and compare to #4, if #5 is blackish then low compression could be the issue, but could be other things as well.

 

[Regular Guy]

Thanks Ron; not being terribly mechanically inclined myself, I want to be armed with good information when I go to the shop.

 

[Regular Guy]

Hmm...light's off, running fine.
Spontaneous remission; how 'bout that.

.

 

[BRUTUS_T_HOG]

Sunken valve seats are very very very common.

A static compression test won't show it, a running compression test will.