Flashing check engine light on 02 Honda Oddyssey after Valvoline oil change.?
Check if any vacuum lines got disconnected. Check intake vacuum with a vacuum gauge. Vacuum is good, check fuel pressure with a gauge.
You stated you declined the fuel filter so why are you asking if it could be the fuel filter was put on wrong. Either way a fuel filter is not the problem. With a flashing CEL the spark plugs are the first thing to replace. NGK or Denso Iridium spark plugs only! Are you aware of the common problem with Honda motors? Thy get tight valves and the valves need adjusting every 60,000 miles.Find a real mechanic and get the spark plugs changed and the valves adjusted. That's how I would approach the situation.