2004 Honda Accord 3.0 Liter V6 Misfires

This 2004 Honda Accord came in with the SES (or check engine) light on. I checked codes and found a misfire code for everyone of the six cylinders. P0301, P0302, P0303, P0304, P0305 and P0306. With a code set for every cylinder plus a random misfire code P0300 I was pretty sure there would be a common fault to all.

The fault as it turned out was the previous repair done by the inexperienced son of the owner. Since I was looking for a common thread and suspected a problem with the spark plugs themselves, I asked the customer if the spark plugs had been replaced anytime in the recent past. She acknowledged that her son had installed new spark plugs about a year ago. I started at the forward cylinder head. The black plastic cover is held on by two screws at either end.

With the cover out of the way, I disconnected the ignition coil harness connectors.

Loosened the coil retaining bolt.

Removed the bolt and pulled the coils out.

The rusty looking deposits on the coil boot is from combustion gases.

More deposits.

The seal at the porcelain base to the steel housing appears to have been leaking combustion gases.

However I was also able to remove the spark plugs using my ratchet as shown in the next picture. The spark plugs were not properly tightened when they were replaced.

Looking at the spark plug crush gasket, I could see that it had never been crushed.

To show the difference in the crush gaskets, I tightened the plug on the left to the proper torque before removing it.

The properly tightened spark plug gasket measures 1.83 mm in thickness.

The one that was not fully tightened measures 2.18 mm in thickness.

It is a little hard to see but I try to always use a torque wrench when tightening anything on an engine. Including spark plugs. I prefer the clicker type torque wrenches. The specifications for the spark plugs on this engine are 13 ft lbs. Please check the specifications for yours.

The torque specs for the ignition coils was 8.7 ft lbs.

After properly installing a new set of spark plugs and clearing the codes, all is well with this Honda. In case you are wondering, the slightly loose spark plugs were not properly grounded and this was triggering the misfire codes. The problem  was slight enough that I could not feel the misfires but the PCM was picking up on them. I am sure an oscilloscope would have picked it up but no sense in adding cost to the repair as it was simple and evident.

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