So my check engine light was on for about 10 days, giving p0171 and p0174 codes for too lean. Mechanic did a smoke test and said my purge valve was bad he advised that, until my appointment to replace (I did not know it was as easy as it is) to run my tank almost empty (we had accidentally filled with ethanol gas), dump in a bottle of octane booster then fill with top tier gasoline. After those actions the check engine light turned off after about 3 hours of driving.

So I have a few questions.1, does this make sense to anyone? And 2, do I need to now use premium gas always and 3, should I still put on the new purge valve I bought?

 

Welcome to FTE Lagwagon777,

Top Tier is a certification, not an octane rating. You should use Top Tier fuel whenever possible. In most cases it’s priced competitively. Makes no sense to save a nickel a gallon buying at some sketchy place with old tanks full of contamination. Their pumps are probably not calibrated either.

If you have an EcoBoost, you should use at least mid grade, and premium when towing.

https://www.toptiergas.com/

 

The inerwebs lean more towards a dirty Mass Airflow Sensor, If you are handy it might be an easy item to clean. I agree with burning top tier fuel, next tank, I'd throw some good fuel system clean in it, maybe Techron or Seafoam. If light went off on it's own, that's a good sign.

 

Most pump gas has ethanol, what percentage were you running (E10/E15 or E85)? If E85 you could have been running lean due to this. E85 has a higher octane rating but it takes about 20% more of it to make the system run properly - which I do not think the ecoboost will account for. Filling back up with a 10% mixture will bring it back around.

 

I get top tier probably around 9 times out of 10. Every now and then some station has a killer deal about 75 cents/gallon less than everyone else. With a 36 gallon tank, that is pretty persuasive.

No one around here puts ethanol in their gas.