Tire size different than factory can make the calculation inaccurate also.

 

But i Dont believe by the differences/inaccuracy that he is encountering.....i think there is a Programming issue going on....tire size cant possibly account for almost 30% inaccuracy in MPG

 

Alrighty. After 2 weeks of spirited driving and resetting my MPG calculator at the gas station, according to the car I have gotten 19.5MPG but according to a pencil and paper I have gotten 26.9MPG. Running the tires that came on the car ( I believe ). Again, I dont mind very much, but I do find it odd and was just wondering if anyone else has experienced this problem.

 

Well, funny I read this. My injector experiments of installing an incorrect injector which happened to be too far off also gave erroneous injector reading that could be a possible explanation. ie, car ran fine and real world mileage was normal, but inaccurate on the cluster. I have also found at least two HHRs that had incorrect parts installed that would create such a scenario, probably as a fault of engine replacement.

I see this thread is older, but the information is relevant. If the Op is still out there and would respond to this, I would be curious to verify year and engine option as well as injector part number to prove or disprove a possible fault and source of the issue.

 

Sure thing! The car is a 09 2.4L and Idk how to check the injector any tips?

 

Ah! glad to see if I could help.

I don't know if you have a check engine light on, exhaust leak, or any other issues, but a quick check would confirm or eliminate the possibility.

Being an 09 2.4 you should have injector 12613163 that are approximately 40lbs/hour. If the injectors of an incorrect flow rate are installed, the car would have to alter the fuel trims to get sufficient fuel, better explained as adjusting the pulse width or duty cycle which is the amount of time the injector is open vs closed. The PCM calculates different than expected fuel based on the calculated flow rate x time injector is open and gives you an incorrect number.

But lets start at the beginning:
Shine a flashlight on them and see if you can locate a part number, color on injector, etc
You should have a solid gray injector. that is the one on the far right, the number would be on the flat surface that faces the driver side.
If it is gray but it has an oval open area, as the one in the center, it is an 06-07.

All five of these are ecotech injectors, but only the 3 on the right are stock HHR applications.

Please update accordingly! thanks!