Sudden increase in Gas mileage

[Hitech]

2006 CTV 127,000 miles LTMPG 59.9

I drive the same round trip 5 days a week 108 miles each way, 60 MPH with cruise, no traffic, flat ground. My tank to tank mileage only varies due to wind or rain but is about 63 mpg. Two days ago I noticed my current tank mileage was 73 MPG so I reset the trip and after 70 or so miles it was over 80 MPG Car was running normally. Yesterday afternoon on my trip home, the usual "stumble" as the engine transitions into closed loop was long and drawn out. Then, about 10 miles into the trip the MIL light came on. Car ran normally for the remainder of the trip (still getting an indicated 84 MPG)......... any guesses?

[joecvt]

That is strange ??? I mean getting more MPG even after the Check engine light goes on....Probably the best thing to do is to get the codes read with a scanner (or goto a place that will do it for you) and then report back what they are. Hard to tell without the code but something as little as a loose gas cap will kick off a code. The strange part is that when the MIL light is set and if a sensor is bad, a default setting is used for that sensor and you would not expect to see better MPG during that time.

JoeCVT = Just your average CVT owner

[MN Driver]

It's funny how you mention that because I have a 95 Geo Prizm (GM's joint venture identical to Toyota Corolla except for interior and body style changes) and when the downstream oxygen sensor went I've received better gas mileage ever since then. The best I had ever gotten was 40.5 mpg on my way home from Chicago to Minneapolis but after the check engine light came on I have seen 40-42mpg on 4 consecutive tanks driving through Michigan to Toronto and back through Michigan to get back home to Minnesota. Earlier in the spring I got 44mpg with it driving through a near-blizzard in Wyoming at the end of March this year. I regularly get around 40mpg with it with my 80% highway 20% in-town daily commute, which I used to almost consistently get 35mpg with last summer. ...Although when the sensor wires were torn out, it is possible the sensor was making such a bad signal that it hurt fuel economy in the first place but the EPA estimate for highway on that car is 34mpg.

[Hybrid-Battery-Repair]

Originally Posted by Hitech

2006 CTV 127,000 miles LTMPG 59.9

I drive the same round trip 5 days a week 108 miles each way, 60 MPH with cruise, no traffic, flat ground. My tank to tank mileage only varies due to wind or rain but is about 63 mpg. Two days ago I noticed my current tank mileage was 73 MPG so I reset the trip and after 70 or so miles it was over 80 MPG Car was running normally. Yesterday afternoon on my trip home, the usual "stumble" as the engine transitions into closed loop was long and drawn out. Then, about 10 miles into the trip the MIL light came on. Car ran normally for the remainder of the trip (still getting an indicated 84 MPG)......... any guesses?

Are you still seeing assist and regen charging?

[924guy]

the sensors may be reporting inaccurately. have you verified your mpg with manual calculations? im curious about this, as my mile-o-meter is actually misreporting, but it is under what im actually getting by almost 2mpg. its showing 45.1, however when i did the calcs after filling up, it worked out to too 46.9 (70-75 mpg highway with ac in econ mode for the curious) on known distances. given that i drive almost 600 miles a week, this is a significant difference. but if there is an unexpected sensor issue that can impede mileage, it would be valuable info for all of us.

[Hitech]

Well, I put my scanner on it and it reported a DTC of 0457 which is the “check the gas cap stupid” code. The cap was tight but the lanyard was trapped between the seal providing an air leak. The calculated mileage did not change. So, I guess the Evap system was purging and the system was acting like a “carburetor”. The fuel injection system just filled in to make the closed loop. The result was high indicated mileage.