1998 Escort 2.0 SOHC - P0304 code

[Gene Brink]

Having a problem that is showing up as code P0304 – a misfire on cylinder #4. Here are some general bits of info and thoughts. I’d appreciate any further ideas or thoughts anyone might have.

1998 Escort 2.0 SOHC – automatic trans

Head redone approx. 10k miles ago – compression good on all cylinders. Engine runs great most of the time.

 

Misfires generally caused by:

Faulty spark plug (all plugs look great – new when head was done), faulty plug wires (new when head was done) – switching #4 plug and wire to #2 cylinder made no change when fault code comes up so believe plug and wire is NOT the problem (also eliminated the coil pack since all plugs are firing as evidenced by plug condition when removed)

Faulty crankshaft or camshaft position sensor – As the problem is intermittent BUT always the same cylinder this does not seem likely as I would expect a faulty sensor to cause a misfire on any of the four cylinders not the same each time (this because the sensors only send an electronic signal based on magnetic pulses caused by teeth on the crank and/or cam).

Faulty fuel injector – as a misfire code will trigger if any single cylinder develops slightly different power than other cylinders this seems as though it could be the cause providing the injector is marginal and fires properly most of the time (which would account for the engine running correctly most of the time?)

Faulty ECM – since it references crankshaft/camshaft sensor input to perform engine management and send signals for timing, injector firing, etc it seems as though this could be the problem if the flaw is a repeatable glitch. How would one check this out?

Faulty wiring or connector – assuming the connection/wiring is marginal this certainly could be an intermittent problem

 

Anyone have any experience with a similar problem and if so what did you do to correct? Thanks in advance for any ideas.

[MattDoscher]

I don't have any experience w/ the 2L Escort.  Just thinking out loud here to maybe point you in the right direction.

 

What kind of spark plugs are in it now?  If they are not the factory ones I would reinstall factory spark plugs.

Does the engine have the coil on plug design?  If so, I would replace all of the coil packs w/ factory ones.  If not I would replace the distributor cap/rotor/wires w/ factory ones.

You could also try replacing the fuel injectors w/ OE ones.

 

Matt

[Gene Brink]

Thanks for your reply, Matt. Here is some info -

 

Motorcraft wires, Autolite plugs (XP5144). Plugs torqued to spec, wires seated just fine - both ends. New coil pack.

Generally the engine runs fine most of the time (sometimes for a couple of months) before the code throws again.

 

Don't think any of the above would cause an intermittent problem on the same cylinder each time so am leaning towards either wiring that is marginal or a faulty (barely evidently) fuel injector with the injector being most likely (my opinion only - nothing in my experience to support this thought).

[MattDoscher]

Hey Gene,

 

Motorcraft wires are good.  What does the owners manual specify for plugs?  If it's Motorcraft, I would install Motorcraft.  The injectors may be something else to look at replacing.

 

I have a '91 Grand Marquis and unless I use all Motorcraft parts the engine tends to be finicky with aftermarket plugs, wires, etc.

 

Matt