intermittent misfire cyl 4/5/6

[eddiewolfgang]

Hi everyone, i apologize if this topic was covered, i just couldn't find someone
with a similar problem i have.

Ok, i got a 2003 exporere 4.0 v6 with 99k
As im driving one night on the highway, CEL starts flashing & cyl 4.5.6 are missing & loss of power, then after like 30 sec it goes back to normal & ck eng light goes off.
When i got home, ck for Fc, got p0300,p0304,0305,0306. Faults cleared on their own the next day.
Here's what i did as far as tune up.
Plugs (motorcraft)

Coil pack & wires
Vavle cover gaskets (were leaking)
Intake manifold gaskets
Changed oil & filter
Perf injector cleaner using special tool & compressor
Techtron sys cleaner in gas tank

Ck fuel press, ckok
Ck for vacuum leaks ck ok
Cleaned MAF

Im trying to narrow it down as much as i can without replacing any parts.
I haven't taken out the plugs yet to see how they look like, but im gonna soon.

Could someone please point to the right direction, thnx.

 

[rmcknight]

i'm completely guessing

only thing i can think of that would cause the entire right side of engine to fail is the right head / (right = front, easy cam chain) timing to be off slightly.

you may be able to check that by pulling the plugs and make sure (#5 i think it is), is fully up. Put a screw driver in the spark plug hole and get someone to turn the engine over with something very slowly and check tdc on crank is where you feel the very top of the piston cycle is with the screwdriver.

 

[eddiewolfgang]

i'm completely guessing

only thing i can think of that would cause the entire right side of engine to fail is the right head / (right = front, easy cam chain) timing to be off slightly.

you may be able to check that by pulling the plugs and make sure (#5 i think it is), is fully up. Put a screw driver in the spark plug hole and get someone to turn the engine over with something very slowly and check tdc on crank is where you feel the very top of the piston cycle is with the screwdriver.

Hope nothing wrong with the timing chain, but even if timing is off wouldnt the problem be there constant or misfire more often.
It only misfires like once out of a 50mile trip of say.

 

[rmcknight]

yes, you are probably right - but it may be the very beginning of something. The other possibilities are less likely - like blown head gasket or cracked head etc. You could just replace all the injectors, they are quite cheap - and easy to replace.

 

[eddiewolfgang]

update

I checked the car with my friend over the weekend hes got a really good 5k snap on scan tool, no codes stored but perf self sys check KOER, heres what i got. (P2197 02 sensor signal stuck lean bank2 sensor1)

so its the o2 sensor before the cat.
Replaced o2 sensors before cat on both banks
started the car, eng @ idle feels alot smoother now
ran another self test with the scan tool, all checked out good no faults

Problem solved

 

[rmcknight]

if you haven't already, make sure you reset the computer, or disconnect the battery for 10 mins.

 

[caspian65]

A bad t-stat can run the motor too cool and cause the O2 sensor(s) to foul out. Temp gauge should be reading about dead in the middle when at full operating temp. Guess the t-stat sticks open on these engines when it goes bad.

 

[eddiewolfgang]

if you haven't already, make sure you reset the computer, or disconnect the battery for 10 mins.

Can you reset the computer with the scan tool too?

Today I drove the car to work, drives so much better & feels a lot more responsive.

 

[rappenp]

Sounds like a weak head gasket, my 04 was randomly having misfires on number 4 throwing codes. a can of stop leak made it stop but then the first road trip Head gasket went left me walking. Changed the head gasket haven't had a misfire since.

Try adding stop leak and check the anti freeze if you slowly lose fluid....

You may be able to re-torque the head not sure about that since it uses torque to yield bolts.