Help with a random misfires problem P0300, P0303, P0304, P0316 | Ford Explorer Forums - Serious Explorations

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Help with a random misfires problem P0300, P0303, P0304, P0316


June 13, 2011
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City, State
Year, Model & Trim Level
2011 Limited
Smart ford owners, tinkers and mechanics;

Looking for assistance, help and advice! We have a 2004 Ford Explorer 4.0L SOHC v6 with about 71k miles on it and misfire problem that I haven't been able to get to the bottom of yet. I have a scanner with live data capabilities if there are other things I should check with that hopefully pinpoint the problem so I can fix it. Here's what I know and the things I've tried / changed so far.

  • Random misfires
    • often shortly after startup
    • regularly inducible between 43 - 48 MPH with RPMs in the 1200 - 2500 range.
    • other more random / inconsistent times
  • Occasionally slow to respond to accelerator being pressed

The only diagnostic codes it gives are P0300, P0303, P0304, P0316

Parts replaced so far:
  • Spark Plugs of cylinder 3 and cylinder 4
  • Ignition Coil Pack
Diagnostic attempts:
  • Check diagnostic codes and read about each
  • Visual inspection of hoses, air box etc no signs of splits, cracks, holes etc
  • Visual inspection of spark plug wires / boots
  • Mist spark plug wires / boots with water looking for indicators of damage / short

I recently had a P0303 and P0316. Check it out HERE. You are supposed to swap the spark plugs and/or COPs to see if the problem follows the cylinder you move them to. If it does that tells you it's probably the components you moved. If it really is random as it move around unpredictably then check out the video I posted above.

4.0L SOHC does not use COPs (coil over plug). 71k is not a lot of miles.
You have misfires on both banks (Cylinders 3 and 4 are on different banks).
Check your crankshaft position sensor, and check (carefully) the outer diameter of the harmonic balancer (for separation from the inner diameter, due to deteriorated rubber bond, a common problem for this engine).

Lots of other possibilities, but might need specialized equipment ot diagnose. Slipped timing (e.g., damaged primary timing chain/guides); clogged fuel filter? Catalytic converters/blocked exhaust?

How are your fuel trims @ idle (when its not misfiring)?

NB: if a bad fuel injector is dumping uncontrolled gasoline in a cylinder (e.g., stuck open), it can dump that fuel to the cat where it ignites, overheats, and destroys the cat.