Owner of a 2008 Honda CRV EX having 76k. Since the purchase the vehicle had lot of ups and downs on mileage fronts. Initially this vehicle provided on a avg 24-25 mpg for regular gas. Live in CT area and use mobil or shell 87 grade. Recently when the vehicle touched 70k, decided to do the service myself. It had OEM denso spark plugs and was suggested to purchase NGK iridium plugs for it. It was mentioned its pre gapped to factory standards. Replaced the plugs, air filter and did a throttle body and MAF sensor. Immediately the mpg freaking dropped like hell. It dropped to around 17-19 mpg. It was really frustrating as whole tank of gas provided me around 250 to 260 miles. Went to stores and got the original OEM dense plugs and replaced it with NGK, but even then no luck. Burnt around 6-8 tanks of gas, yet no improvement. I was really frustrated and got all the fluids checked and replaced, yet no luck. Finally I decided to take it garage to get the ECM module reset. the whole reset job costed me $250 and when checked the plugs were clean. Burnt around 2-3 tanks of gas yet no luck. No person or computer provided information on any issues with the vehicle. This was really frustrating.
Finally was reading through some articles and some expert had mentioned that plug which comes pre gapped to factory settings sometimes might not be correct. Honda recommends for CRV having plug gaps to 0.4 to 0.44mm. The plugs I got was 0.42mm. He had also mentioned that close gap reduces mileage and readjusting to larger gap sometimes have improved mileage in few vehicles. Taking this a hunch I regapped the plugs to 0.45mm. Did a manual reset of the ECM by disconnecting the battery terminals and shorting the wires to clear any charge retained. reinstalled the plugs and connected everything. Started the vehicle and let it idle to relearn everything for 15-20 mins. after warming up shut the car to save the learned parameters and then started again to take a test drive. Amazing thing was the vehicle was really really smooth and was gliding. It was quite surprising and filled the vehicle with a whole tank of gas. It started averaging to 24-25 mpg again and freaking ride is smooth like hell. I am really awestruck how all of a sudden this difference is made to increase the mileage when it is regapped to 0.45mm. Sometimes it even gives me 26mpg. Can someone who is expert help me answer this mystery when no computer or expert mechanics were able to find any issues before on the mpg mystery. Jeez now constantly I am getting avg 25 mpg. Yes!! its strange yet but true. share your views please.