Fuel Consumption Increase after Recall 3305G service
 

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.

My experience was that the 3305G recall has given me slightly better gas mileage (.5 to 1.5 miles/gal). My car is an MT GT that was built in 5/2003 and had been running with the M flash. I do mostly in-town driving.

FWIW

Glad to hear of your experience. Frankly, I'd be thrilled if this is specific to my car as I can get it dealt with. I'd be more concerned if it were a widespread problem. I have an '04 GT (AT) - married, doncha know. Hope more owners chime in.

Your assumption regarding PCM re-programming may be incorrect,you may wish to read the details given in the Recall repair procedure which indicates the changes in PCM programming involve logic modes which prevent extended high rpm under conditions which could cause heat damage.
I noticed no difference in fuel consumption after the re flash.my fuel consumption has ranged from 10 l/100km to 13 l/100km,but I do not drive it in winter.

I believe you are correct that the 3305G PCM flash changes are only for the high RPM limits. However, these changes are applied on top of the previously top-level PCM update. Hence, the changes you experience in you car are a function of what PCM level you were running prior to the recall. For example if you were at the R flash level you should see no change. If you were at the J flash level, the change could be dramatic.

I've also experienced a significant decrease in MPG since my recall service.

Gas mileage worse
 

I too have experienced this. I used to be able to drive about 220 miles per tank now I can barely get over 190 miles per tank. I recently had the recall performed and will be taking my car in over the next week to have it looked at. Thankfully it is still driving good!

I had the recall work about four tankfulls ago, and I really can't comment one way or the other as to the gas mileage. The first tanks seemed a little lower than my previous average, maybe .5 to 1 mpg less, but that coincided with a significant drop in outside temperature, which normally decreases mileage.

A new flash also resets the memory of my particular driving behavior, and I expect that once the computer "remembers" how I drive, my mileage should increase.

I was at M before the recall work.

Many areas of the U.S. require the use of oxygenated gas during the winter months. Oxygenated gas gives less mpg than the gas you get the rest of the year. It could be that the flash has nothing to do with it, and it is just happened at the same time as the introduction of the oxygenated gas in your area.

I recently saw my mpg drop by 1-2 and hadn't changed anything. The only thing I could come up with is that the gas changed sometime in November to the winter blend.