Wont Maintain Speed.
 

Howdy all! I'm relatively new here so if some one has had this problem and had it anwsered please direct me there I used the search function to no Avail... ok the problem I am having with my 2004 RX8 (it's the automatic transmission with sport shifter) is while i'm driving it, it will sometimes take a while to accelarate up to speed regardless of how hard or light I put my foot on the gas, eventually I finally get to 50MPH and it shifts to 4th grear and this is where the problems begin, it slowly but surely starts losing speed and if I keep pushing on the gas it will down shift to 3rd take me up to 54 or so MPH then shift to 4th and the process starts ALLLL over... I've changed the battery recently which made the problem go away for a while at least.... but I'm just looking for some help before having to spend even more money on this car then I allready have. ANY help is appreciated!

Cheers:beer05:

I'm thinking it could be one of two problems. First and most likely, is the catalytic converter is clogged. Drive it for a little while and look at the cat, under the passenger seat. See if it is glowing red. Second possibility is the fuel pump may be bad. When they get hot, they begin to cut out. Putting fresh cool gas in the car will immediately correct the problem.

The Cat is under the passenger seat? ok i'll check that out. so Fuel pump eh? oh also when I first drive it at the begining of the day it works fine it's after it's been running for a bit. I also think i might have messed up and gotten gas at a place I KNOW sells crapppppy gas... if I did do that should I put some Techron in the tank? also if it is the Fuel pump is it something I can change myself? I have a great deal of knowledge with mechanics.

If it is the fuel pump, it is located under the drivers side rear seat. There is a plate that covers it. The worst part about removing it is the ring that holds it in place. Mazda has a special tool that costs about $150 to remove that ring. Maybe you can borrow one from a local dealer if you have any kind of relationship with them. NAPA online sells something that looks like it will work. Others have used a hammer and screwdriver to remove the ring. You have to be careful using this method. I was able to borrow the correct tool to do mine. Beyond that, it is pretty straight forward. There is one electrical connector and 2 hoses. One is an output to the engine and the other is the siphon from the right tank.

You can buy a replacement pump assembly from the dealer or a pump insert from Black Halo Racing
https://www.rx8club.com/series-i-major-horsepower-upgrades-93/fuel-pump-solution-all-failure-modes-176491/

I am in pretty good with the local Oriely's, they let people loan out tools and if they don't have it they will order it for you to borrow. ok SO drive it for a while get it up to temp then stop to see if the Cat on the passenger seat is glowing red, if it's not that it's more then likely the Fuel pump. if it is the Cat, I'v replaced them on Domestics before but never an import and nothing newer then a 98 hehe so i'm guessing to replace the cat i will for sure need to go to a dealer...?

There is a warrenty on the catalytic converter for all cars sold in the US. It is 8yrs/80K miles. If your mileage is over that you have 2 options. One, wait for one to show up in the classifieds on this site. They do intermittantly. Two, get a high flow cat as a replacement. One more if your not in an area that requires emissions testing is to replace it with a midpipe. This will cause a MIL/CEL to show up.

sweet i'm at 66677 today Ironic I know.... >_> so take it to the dealer if it's the cat?