August Fix of the Month: Honda Odyssey Misfire

Ever had one of those cars that you think to yourself “Why am I in this career?” Tech J did. 2002 Honda Odyssey with a 3.5L V6 Engine with codes P0300, P0301, P0302, P0303, P0304, P0305, P0306. The van ran like a 2 cylinder turtle up hill. Vehicle had been to several shops trying to fix the issue.  Technician J being the advanced diagnostician as he is, started with the basics. ALWAYS start with the basics! He quickly realized this was not an easy problem and immediately pulled out the Snap-On Scope.

  1. Checks battery voltage, alternator diode ripple, voltage drop tests on the ground wires. Good. 
  2. Next is the infamous Relative Compression Test – tests good BUT…..
  3. Wait! The vehicle stops misfiring when it gets warm! Ah man!
  4. Let vehicle sit overnight. Now it’s misfiring. Let’s look at our pattern. (Tests Bad)
  5. Now let’s line up that low compression hole and figure out which one it is(#6).
  6. Next let’s find out WHY! Perform cylinder compression scope.
  7. The scope revealed the exhaust valve was not sealing.
  8. Customer approved complete valve adjustment. Problem fixed!

Customer brought the vehicle back about a week later. Uh oh! Now what? Same codes! After scratching our heads for a long time and not being able to duplicate the concern, Tommy had an idea. Disconnect EGR system and see if problem persists. It went away. Now comes the several shops part…..they always say a man-made problem is the hardest to figure out. Turns out the EGR plate on top of the intake plenum had been put on backwards. Reversed the plate and all is good here in Denton TX. Vehicle passed State Inspection!