I have had problems with my 8 not running well for a while now. Mazda ran a diag a couple of times, and it always looked like the problem was with my fuel mixture. The car wants to run too rich. I installed the RP Supercat on my 8 back in September and didn't start having any issues untill about 2 months ago.

I pulled the supercat off and reinstalled the OEM cat a few of weeks ago, and cleared both the NVRAM and the KAM. (I only did this because Mazda kept blaming the aftermarket part) But as I expected, the problems didn't go away. Even after driving around 300 miles (mostly interstate) on the car after the reinstall. So I let Mazda have the car for a couple of weeks while I was out of town. I got the car back this morning, and it does seem to be running better. But no more so than it does every time I reset the NVRAM, which is always short lived. Mazda is saying that because the PCM learns progressively, it needed longer to work through the bad information the supercat had been sending it.

So here is where I'm looking for some input from the forum....
1) Does it sound like Mazda has a legitimate argument considering the car ran fine for 4 months with the supercat installed?
2)Has anyone else had a similar issue with the RP Supercat, or any aftermarket converter, after installing it on their 8?

I'm driving to Oneonta for a funeral this afternoon, which is little over an hour in both directions. So I'll update my post after the trip to see if the car is still running better, or if it looks like Mazda just reset the memory.

Update: It looks like I was right. Mazda doesn't seem to have done much more than reset the ECU. It was as bad yesterday as ever. It even reminded me of a couple of symptoms that had slipped my mind:

Very sluggish throttle response

Have had to drop down to 3rd to accelerate uphill - when driving around 50mph+

almost stalls at red lights - and has stalled a couple of times

Coverter gets pretty hot

Car backfires - particularly when I shift

When the A/C compressor turns on the RPMs drop, sometimes as much as 500 (tested this at low RPM though - specifically with car in neutral, dropped from 2.5k to 2k
-addition to that- when idling with the A/C on, the RPMs want to hover just above 500 and if I'm not mistaken it should move from 800 to 1k to compensate for the added drag

Car feels like it has what I can only think to describe as a "miss". It feels a little like someone touching the brake for a split second as I'm driving, The timing of it is completely erradic, and it's most noticable when I'm maintaining a constant speed. Generally with the RPMs holding very steady (between 4.5-5k)

Symptoms are always the worst in the afternoon when it's warmer. The car still hasn't thrown a CEL though.

 

If anything it should run leaner...did it set + LTLT? or -VE?

It would be more likely that you have a stuck injector...or fuel pressure problems

Did they check the Fuel Pressure....if the regulator isn't working properly then it will raise the FP and cause rich running.

Could also be the MAF...if it's reading higher than actual...PCM will inject more fuel than needed...and the O2 sensors will pick it up ....and it will throw a 0172 ( too rich) code or such like


Give us a bit more information......

I would highly DOUBT that it has anything to do with the supercat

 

Sounds like you need a compression/vac test.

Those symptoms smell of bad compression......

It will throw a CEL for running too rich...very quickly if the A/F are way out so you need to look elsewhere

Despite what they say...you won't get codes for a lot of things...

Push for the compression/Vac test

 

supercat is most likely not the culprit here. Keep in mind that our cars run very rich with OEM programming in an attempt to lengthen the life span of the OEM cat.
I data logged my car with OEM PCM values and I was getting 11.02 AFR's at WOT.

The 3 figures that CRH listed above are probably a great start.
Have you ever replaced the plugs of the coils?

 

I replaced the plugs, wires, and coils 4 or 5k miles ago. Changed the coils again about 1k miles ago when all the problems started. I pulled them off to check, and one had some of the milky marks on it.

 

You might want to switch dealership.

 

It would be unlikely to be the CAT when you had 2 doing the same thing..

I still think you need to get the tests that Charles and I wanted..before we can help you out much more.

Like nycgps said...It might be time to have someone else look at the car...they aren't doing much where you are taking it now

 

I have been going to Med Center since I bought the car. Mostly because I've become friends with one of the service reps and he has helped me out a few times. I like to show some loyalty to people who go out of their way for me. But the line has to be drawn somewhere, so...

Just got off the phone with Trussville Mazda. I explained the problems with my car, and specifically asked if they would run the compression test (and test the MAF sensor). He said they would. We'll see. I'll ask for a copy of the results and post them first chance I get.

 

Let me start by saying I am SO glad I took my car to Trussville Mazda! It looks like the 8 is finally going to get fixed. Now, lets get to the explaination.

So everything makes sense, I need to tell everyone what went on with the 8 back in January. My coil packs went bad and started dumping fuel into the cat. It got super heated (a few times b/w getting home the night it happened, taking it to Mazda, and Mazda test driving it). That's when I replaced the spark plugs, wires, and first set of coils packs It also fried the O2 sensor. Fast forward to the end of March, when all my problems started. Med Center told me my fuel mixture was off and the converter was the cause. But every test implied the converter was fine. I suggested the wiring harness could have been damaged by the heat way back when. They "checked" it, said it was fine.

Here is what I learned when Trussville Mazda called me yesterday to give me an update...
The tech told me he was getting a lot of "U" codes from the PCM (unfortunately I don't know enough to know exactly what that is). So after looking up the car's history, he checked the wiring harness on the O2 sensor. It seems I have been driving around with an incomplete electrical circuit, and no ground wire on my O2 sensor. They are going to replace the harness, the sensor, and the cat. Depending on what that does or doesn't correct, I might even get a new engine. Needless to say, I never got a compression test, but thanks to everyone for their help.