I purchased a 2005 Honda Odyssey with over 240,000 miles a month ago, and it was running perfectly. A few days later, at a stop light, it started to shake, misfiring, and the engine light began to flash. Discount Auto Part is in Phoenix, Arizona, for a free diagnostic test. The results indicated the spark plugs were misfiring. The clerk suggested new coils may be necessary if the symptoms persist.
The new spark plugs and coil didn't stop the misfiring/ or the engine from shaking. We plugged it into the computer to see if there was any difference, but you could see and hear that the problem sounded noticeably worse. While the engine light kept flashing, the Van continued to misfire and shake as it idled. The only other thing we did was use a Molly - an additive for the gas and another for the oil, resulting in a better overall performance. Still, the shaking misfiring and engine light persisted.
The consensus among my mechanical buddies is :
1) Due to the mileage, there could be a lot of sludge in the bottom of the gas tank, causing the Van to misfire and shake. Solution: Keep the gas tank filled between the quarter tank and 3/4 full and continue to use the Molly gas additive to see if that solves the problem.
2) Add Molly oil additive to your following oil change.
3) If these two strategies fail to solve the root of the problem, the next option might be a Valve adjustment and timing belt replacement.
4) Motor mount issues
5) Camshaft issue
Ok, Mr. Online Mechanics, that's my story; any questions, observations, insight, or suggestions are welcome.
Thomas
The results indicated the spark plugs were misfiring.
What exactly were those results? How did they test the spark plugs to come to that conclusion?
The clerk suggested new coils may be necessary if the symptoms persist.
Possible of course but it does not appear there is enough information to draw that conclusion. Was the clerk a mechanic?
The consensus among my mechanical buddies is ...
Given the age and mileage it could be almost anything. A complete diagnostic scan checking for codes and an analysis of live data would be a good place to start. You will also find troubleshooting information in the site FAQ.
Please don't hijack an old post from August, start your own topic. It makes more work for the moderators on this site. A 2005 Honda Odyssey has almost nothing in common with a 2021 Odyssey.
Motor mounts wouldn't cause misfires., the car will just shake all the time.
Start with adjusting valves. I don't know whether or not that engine is an interference engine or not, but, if there's no record of it being changed and it is an interference engine, I would change the timing belt.
