Gas Heat Shield / PCM Recall and Crappy Gas Mileage
 

Recently, I took my 2004 RX-8 to my dealer to have it serviced per Recall 3305G(Heat Concerns During High Idle). As other owners may be aware, the service included installation of a heat shield near the fuel tank and a reprogramming of the PCM. Prior to the service, I was lucky to get near 350 km per tank. As we don't drive Chevy Sprints and I generally love my car, I was able to live with this economy. Since the service, I'm lucky to get barely over 300 km per tank. I use premium fuel, have the car serviced regularly, and maintain 32 psi in my tires.

I am assuming the PCM was reprogrammed to increase the amount of fuel in the air/fuel mix to result in cooler exhaust temps. Oxygen sensors in the exhaust stream can be used to calculate the air-fuel mix ratio in units (lambda). Maximum power for the RX-8 is generally seen around the 0.92-0.93 lambda range. If the mix is too rich with fuel, the lambda figure will be lower. If the mix is too lean, the lambda figure will be higher, increasing the risk of detonation in the exhaust. A lower lambda figure will often result in both power loss and reduced fuel economy.

I sense the latter has happened with my car. I have contacted Mazda Canada and alerted them to my concern. I was directed to take my car to my dealer to have it checked over and will be doing so this week.

I urge any other owners who have had a similar experience to immediately contact their dealers to have their vehicles checked and to complain if they are not happy with this turn of events. As RX-8 owners, we were not given a real choice on the matter as the Recall letter refers to having the service performed or risking warranty breach. Frankly, it should not be my problem if Mazda designed a vehicle that was not properly designed or engineered. I bought a vehicle that has an advertised fuel economy rating of 12.9 and 8.8 L/100km - I had been living with a figure around 17. It is now slipping closer to 20. This is simply not acceptable. The manufacturer will only pay heed if enough owners raise this as an issue. Please contact your dealer if you have shared my experience and frustration on this issue. Cheers.

After the ECU flash, my fuel economy went from 17 in town to 19...since, it's worked it way back down to about 15-16... :(

No idea...

My fuel economy dropped significantly as well after the re-flash. I was usually in the 20-21 mpg range, now I'm almost always at the 18-19 range. I did have a change in my normal driving route now, with more back roads and less freeway, so that may be the reason why.

Hard to say, so I've not complained.

Now maby I changed my driving ways, or not, but I SWEAR i was getting 270miles per tank, after the recall 230miles. Heck i might be off on how much gas im using but I did notice a significant change in milage.

You guys are lucky. I just filled up my tank last night. My fuel gage was nearly pegged on E. I reset my trip odometer with every fill-up. I had 198 miles on that tank. After the fill-up I checked to see how much I put in and it said 14 gallons. So that calculates to 14mpg. I do most of my driving in the city and I rarely drive it hard.

I just bought the car a month ago and it doesnt have 1000 miles on it yet, but its getting close. So the fact that its new may be the reason I'm getting bad mileage. Not sure how you folks are managing over 220 miles a tank.

Mine has dropped also :(