[visionguru]

I noticed high fuel trim long time ago, the long term was 7%~8+% and 9%~10+%, and gas mileage suffered:

https://www.driveaccord.net/threads/7th-gen-accord-mpg-thread-post-your-mpg-here.3253/page-34?post_id=6143793#post-6143793

I did valve adjustment, valve cover gaskets, new O2 sensors, new MAP sensor...., none made any difference. Yesterday, I replaced the vapor canister purge valve, trying to get rid of the annoying "check fuel cap" message. Today, I hooked on the OBDii reader, to my surprise, the long term fuel trims dropped down to 3.8% and 5.7%, more than 3% drop, AND for the first time on this car, I noticed negative adjustments in the short term fuel trim. The purge valve seems a big contributor of the lean condition, and is the root cause of "check fuel cap" message.

 

[capkirk123]

If it jammed open, I suppose it could have acted as a vacuum leak and caused those high fuel trims. I'm surprised it had thag large of an effect.

 

[visionguru]

If it jammed open, I suppose it could have acted as a vacuum leak and caused those high fuel trims. I'm surprised it had thag large of an effect.

Yeah, it puzzles me too. I always thought the V6 air flow is measured by the MAP sensor, a little bit vacuum leak doesn't matter, then I realized that the MAP sensor is located near the throttle body, but the vapor is routed to the middle of the intake manifold.

Here is today's result:

A week ago, I hit a small bump on the highway, then the "check fuel cap" message immediately came up, after about 10 minutes, I got check engine light.

After reset, it hasn't come back. The low purge flow prompted me to replace the purge valve. Somehow, the $20 purge valve made a big difference in the fuel trim figures, while new O2, MAP, EGR,PCV.. did nothing .