i'm really hoping I don't get flamed here.. maybe I deserve it for the choice I made with the gas, who knows. i've got a few different factors to throw into this though.

first off, I just picked the car up from a dealer on Thursday. drove the 120 miles back home (hard to find MT's around here), seemed to be going great. was watching the mileage, just out of curiosity more than anything, knowing the nature of the beast and trying to learn it. was guessing about 13-15 mpg initially, based on traffic and driving style. that's fine I love the car! however, day two, the car threw a CEL. Autozone said the infamous P0420, the one with the faulty cat. weird. as a sidenote, while talking to the dealer, they mentioned one of the things they did while inspecting it in their own shop, they replaced the o2 sensor. I only mention this because I ran across a thread on here from a single replier that the car complained about a non-oem o2 sensor being installed... don't know if that is common or not.

so then, the second full day, yesterday, we take a trip out of town. we fill up on the way out. here's the catch that i'm embarrassed about... I had heard that premium could be replaced by regular with a bottle of octane booster. THE ONLY REASON I even tried this was because the moron gas stationI stopped at only had 87 and 87 ethanol free. ugh. but they had boosters inside. so I grabbed one and filled up. since then... and this is cruising at about 60-65, I went 100 miles, and i'm at a HALF TANK. whoa. okay if I was driving hard through the gears, great. but highway cruising?? that's like 12 mpg! there's something wrong. i've read up on peoples experiences with 87 and it just doesn't relate.

what this all comes down to is the mpg being unnaturally low, even for this car. is it possible it's one of the things i've mentioned so far?? there are several variables on too short of a timeline for me to tell, when i've had the car less than a week...

don't get it twisted, I love good mpg, but I know this car is like that. I just want whatever is wrong, fixed, because this isn't even normal for this car...

 

A) If you have a CEL, give us the code #. There isn't a code number that corresponds to "faulty cat", and a "faulty cat" can throw one of several codes, depending on the issue. I'm not saying the diagnosis is wrong, I'm saying we can't tell you if it is correct or not.

B) Octane booster labels indicate the number of "points" of octane increase. A "1 point" gain with 87 Octane base is 87.1, NOT 88. So, start doing the math on how much booster you have to buy before it will get to 89 octane. Vs the cost of just filling up with 89 in the first place.

C) If your engine is running smoothly on 87 octane, you have low compression. A perfect compression Renesis will run like complete garbage on 87 octane. As you lose compression, your ability to run lower octanes will improve. This isn't a good thing.

D) 100 miles on half a tank (indicated) is about 200 miles by the time you hit the 13.1 gallons-burned mark where the light comes on (2.8 gallons remaining), which is 15.2 mpg. This is exceedingly low for highway mileage. This could either because of the "faulty cat" noted earlier (as your cat clogs, it will stress the engine more and gas mileage will plummet. A nearly completely clogged cat will return 9mpg highway driving). It could also be related to engine compression, as compression loss decreases efficiency.



Did you get a compression check before buying? I'm guessing "no".

 

a) P0420 is the code.

b) yea.. I read up on that earlier today on here. which was after I did it, of course.

c) >.<

d) interesting, did not know that about cats... where did that quote come from?

you are correct, that was something I overlooked when I asking the questions about current condition. i'm supposed to be getting a list of service items when I go back up there in a couple weeks to have the sunroof hooked back up (they seem to have forgot while replacing the airbag wire harness before I bought it), but there are a few things I'll be asking them about on the phone tomorrow... i'm not waiting that long. thanks for the info, if anyone has more to add, please do!

 

Oops, I missed the CEL code in the thread title


D is my own experience, plus what I see from other posts. When my cat failed my mileage started plummeting, and bottomed out at 9mpg. Not coincidentally, this is the same mileage someone will get flogging their 8 at the track. It's basically taking "full throttle" to move around. There is a whole mess of problems you are starting to cause at that point (I dealt with those too).

You don't note the mileage either, but you should have some sort of immediate post-purchase warranty coverage from the dealer you bought it from, in which case I'd HIGHLY HIGHLY recommend getting a compression test at a Mazda dealer before that runs out, AND get the cat ($1,300) confirmed as dead and replaced. If the engine is low on compression, get it replaced under that post-purchase warranty before it runs out and hope to get one from Mazda under the 8yr/100k engine warranty, assuming you are still eligible (2004s are expiring now, even if they haven't passed the 100k mark).

 

I was already planning on stopping at the local Mazda dealer for the comp test. as far as the warranty goes... I got a short 1 month/1000mi powertrain warranty from this used dealer, but to be honest i've never really utilized a warranty and don't know the stipulations on when they do and do not apply. for example I'm the 2nd owner, does the manufacturer warranty apply to me?? was thinking it didn't so I don't get how the 8yr Mazda warranty could tie in here. and I would think the cat applies with the one I have from my dealer... cat counts a powertrain, right? setting as the CEL came on after buying it. unsure about the comp test and if anyone would cover it... anyway, I filled back up on premium tonight. averaged about 15 mpg on that trip.. ouch. but, it certainly feels more lively. hell, for all I know, it could have been limping pretty bad and I didn't notice.. i've only had it 4 days, and I don't know what a rotary feels like when its running rough yet! so we will see. but I can definitely see the cat contributing here on mpg based on your comment.

calling the dealer tomorrow.

 

A few points.

A) Don't be scared of requesting warranty coverage. You have it, and you certainly look like you will need to be using it.

B) The cat is covered under a federal 8yr 80,000 mile warranty from date of first purchase. Dealers must cover that BY LAW (unless they can come up with a reason not to, such as tampering, damaging, etc...). The cat is not considered to be any part of the powertrain.

C) The 8yr 100,000 mile Mazda engine warranty covers the engine, and only the engine. It doesn't even cover the fluids that go in/through the engine when an engine is being replaced. As with all FACTORY warranties, they transfer with the car. However, the service records usually don't transfer with the car, and since service records are usually requested, this makes it harder to get warranty coverage on high ticket items (like an engine). The short warranty you have from the used car dealer will NOT Have the records requirement. They know you won't have them, because they just sold the car to you. It's a "we believe it's fine" warranty. And frankly, I haven't seen a single used car dealer sell an 8 that has any clue what they have on their hands. The ones that do actually know, won't be picking them up to sell.

D) I see you added your year under your user name. If you have less than 100,000 miles, your first order of business needs to be to call up Mazda North America customer service and request records information on your 8. As a 2004, it is already outside of the 8yr time limitation if it was sold any time before February 14th 2004. And yes, LOTS of 2004s were sold in 2003, so yours could easily be one of them. If you are outside warranty coverage for that, then the only thing you have to fall back on is the short warranty from the used car dealer.

E) The used car dealer WILL NOT be able to perform a compression check on a rotary engine. Unlike a piston engine where you can get an analog tester and just watch the needle, you need an electronic tester specifically designed to capture each of the 3 different faces of each rotor (front and rear) along with the cranking speed of the test. A Mazda dealer usually charges between $80 and $150 for a compression test. If the engine fails compression, you should be able to get the test AND the engine replacement covered under the used car dealer's warranty. Telling the Mazda dealer that you have this other warranty up front will 'grease the wheels' with them and make it less likely that they will give you crap or try to come up with reasons why it actually does pass the test (yes, it happens). Dealers make a lot of money off of an engine replacement, the irritating part for them is all the paperwork if it's a Mazda covered replacement. Having some other organization handle that makes it all better.

F) A good engine with good ignition and a healthy cat (or no cat) will be able to easily get 22mpg highway cruising.


So, you have every vested interest in getting your engine checked out before the short warranty expires. They gave it to you for a reason. Pay the cash up front for the compression check ASAP to make sure it doesn't go to waste if your engine is bad. Don't wait to find out 2 months from now.


...and you might want to look through the first 8 posts of my new owner's thread here: https://www.rx8club.com/new-member-forum-197/new-potential-owners-start-here-202454/

 

...err, check engine light went off by itself. >.>

wtf??

 

They do that, that does not mean the problem is gone. Some of the emissions tests are always being judged and checked, it may have reset it but I bet its still in "pending" status.

This car really has trouble figuring out if the cat is in place and working properly. I reset my cel(p0420) several weeks and over 400 miles ago and it still has not come back. That is with a midpipe on the car, and it currently has the cat listed as "OK".

 

so then regarding engine replacement if I need it, you mentioned greasing the wheels with the used dealer covering it.. are you implying I actually don't have to go all the way back out to the used dealer to have this done, but rather a local Mazda dealer can/should do it? that's be great, the used dealer is like 100 miles away...

 

The used dealer CAN'T do the compression check. You need a Mazda Rotary Compression Tester. Get it done at a Mazda dealership, along with the cat check, tell them that it is under a post purchase warranty from a non-Mazda dealer (which should remove most of their resistance to doing the work). Insist on a visual inspection of the cat, not just an ODB2 check. Assuming the cat or the engine fails, send the results to the used car dealer, and/or have the Mazda dealer send it. Proceed from there with warranty replacement.

 

good stuff. scheduled for tomorrow morning at the Mazda dealer. going to push the thorough cat check. now regarding gas mileage... in the past 2 tanks, its gone from ehhh to rock bottom. at the rate i'm going right now, i'm at 9 or 10 in town. this is kinda fast for a bad compression engine, no? you said the cat makes mileage decline fast, how fast??

 

oh, and by driving back out there to have this done, I was referring to the actual engine swap if it came down to that...