Mazda Talk Forums

Approx 3K miles after the install of the Cosworth SC and the full GWR exhaust I finally got my first check engine code. I understand it's probably related to an O2 sensor and maybe spacing it out is a fix. However is it just a Miata issue or is it related to the mods or ? I cleared the code with my DashDyno ~ 100 miles ago, so far no code recurrance. What can I expect? What to do? What's the Illinois EPA sniffer gonna tell me when it's time for them to invade my ECU ?

Pretty common with the supercharger. I know Mike at MotoEast now has a means to shut off the codes for good with his latest reflash. Assuming you have a MotoEast tune in there, you might give him an email on it.

Thanks for the reply. What is actually occuring that causes the code ?

Could be several things. In the cold of winter just cold weather can be enough. But since we are in Summer and this is a supercharged car it is likely running a little rich since install and burning out the cataylst too fast. It can also be a sensor that is a little more sensitive than most. It can be damage to the sensor or the wires to the sensor. We will often start by backing that second sensor a little out and sometimes that takes care of the light for months....to years (Google "o2 sensor spark plug defouler").

Which TUNE is running in your Miata? DPTUNE or MotoEast?

We are having a "cool" snap compared to the screamin hot summer we've been thru.
Running a Moto East tune.
Mike sent a new file to reflash and I will install as soon as I get the DeltaForce installed and figure out the procedure.
Maybe that will be part of the solution.
Thanks for your comments

P0421 is titled Warm up catalyst system efficiency below threshold in the Mazda repair manual. Under possible causes it lists exhaust gas leakage, A/F sensor and/or HO2S sensor looseness, TWC deterioration or malfunction and PCM malfunction. TWC means the catalyst, PCM means the engine computer. In the repair section it steps through these 4 causes in order: fix any exhaust leaks, check the O2 sensors are tight, then replace the catalyst and PCM in that order to "fix" it. Not much help from the official manual, sorry.

As far as inspection for the state goes, use your Dash Dyno to check that there are no codes and no pending codes before you go in for an inspection and you should pass. I don't know if Illinois does a visual or tailpipe check in addition to plugging into the OBDII port.

morrisg wrote:P0421 is titled Warm up catalyst system efficiency below threshold in the Mazda repair manual. Under possible causes it lists exhaust gas leakage, A/F sensor and/or HO2S sensor looseness, TWC deterioration or malfunction and PCM malfunction. TWC means the catalyst, PCM means the engine computer. In the repair section it steps through these 4 causes in order: fix any exhaust leaks, check the O2 sensors are tight, then replace the catalyst and PCM in that order to "fix" it. Not much help from the official manual, sorry.

As far as inspection for the state goes, use your Dash Dyno to check that there are no codes and no pending codes before you go in for an inspection and you should pass. I don't know if Illinois does a visual or tailpipe check in addition to plugging into the OBDII port.

morrisg
They used to do a tailpipe and undercarraige check but now they just plug in to your OBDII port to gather some data and your done.
thanks for the reply
Tom

Just found this post while browsing. You said it is a P0421 CEL. That's not good. All the CEL means is your cat, the one that is very expensive (being part of the header) isn't working. I had all sorts of trouble with my SC'd car, finally Mike Mann corrected the tune. The original tune was by FM, and was bad. When I installed a new mid pipe, I could see into the primary cat, using a flashlight. NOTHING in the cavity at all, looked ilke it was punched out. Got the PPE header, and it has a cat (visual inspection), and the car now has no CEL. The OBD2 monitors have finally reset (first time in almost two years of being cosworthed), and the missing cat was the cause.
It would be easy enough to unhook the mid pipe and have a look-see to see if the cat has vanished into the night. Mine did, your's might too.
slow_eddie

We have a steady stream of customers here with supercharger kits sold by Flyin Miata using tunes by DPTUNE that don't work. We are keeping Mike at MotoEast busy with all the customers needing their installs fixed. We too had tried a DPTUNE in our own supercharged 2007 and had nothing but problems with it, and Joe at DPTUNE was unable to make it work over several months of trying, including sending multiple ECU units back and forth to get the latest versions, none of which worked well enough (Flyin Miata was kind enough to eventually give us a refund when Joe was unable to fix the problems). We too then went to the MotoEast tune and the car has been amazing ever since. Nonetheless, even with the far superior MotoEast tune any boosted car will burn through the converters MUCH faster than normally aspirated cars. Think of it this way, force feeding the engine more air and fuel inevitably means force feeding the converters much more too....and converters are a wear item, working overtime in boosted cars they need much earlier replacement.

A P0421 has nothing to do with the tuning on any of these cars. It is simply the ecu not seeing the noted difference in cat efficiency that it is programed to see. Cars running without cats will see this, unless you remove the BIT that signals the light, run a cat between the two sensors, or use our mini cat in the second sensor position. Both Dynotronics, and Motoeast can turn off the light for you if you run uncatted.

As far as our tuning, let me assure all of you, we stand behind our tuning 100 percent. If you have any issues, please feel free to contact our office,Flyin Miata, or me directly via email or phone, and we will proptly address them and get you fixed up.

BTW, Brian, you are not quite correct here; if the tuning on the SC car is too rich, it will eat the cat. Likewise, too lean will do the same. But there really is no reason the install of a FM supercharger should cause a cat to fail on its own. Flow wise, the fatory cat is more than large enough to handle the increase( notice I said the cat, not the tubing, or manifold), and there should be no increase in EGT, assuming proper mixture.

BTW, we have a customer bringing his 06 with sc to install one of your new catted manifolds next week(or two). I'll be happy to share the results with you vs the PPE they have on the car now, if your interested. I'm hoping it does well since the price and quality look so good