Hi all, wow it's been a while since I was on here, good to see you're all around

About 2 years ago, I purchased the midpipe and headers from here (from Brian) and had them installed. Purrrring beautifully. About 15 or so months ago my engine light came on. Took it back to Mazda, they told me the front oxygen sensor was stuffed and needed a new one. As my car was under warranty then they replaced it for free and it fixed the problem. All hunky dory (Aussie terminology ) from then on.

About 4 weeks ago, the engine light comes on again. Thinking it was the same thing (stuffed oxygen sensor), I take it back to Mazda and they plug it in their computer and it says that the front oxygen sensor again is not responding. Something about it not heating up/warming up at all. I replaced the sensor again with another new one as per Mazda's recommendation, only thing is, engine light is still on.

They are now telling me that the only possible thing it could be if not the oxygen sensor (which is new) is the PCM (aka the computer). They believe that if this is replaced with a new or used one from a wrecked NC then it will definately fix the engine light/sensor issue as that's the last step in the process of elimination. (First the sensor and 2nd the computer).

The computer brand new from Mazda costs AUD$3900 and from a wrecker I can get it for AUD$1750, still a lot of money. I don't really have a choice here because I can't drive forever with the engine light on, naturally it's sucking in more fuel and not running as good as it should. Before I spend this money, can anyone offer some advice as to A) whether this will actually fix the issue or B) what could be causing it?

Mazda seem to believe that it is because I have modified the exhaust system (which is BS in my opinion). Any help would be greatly appreciated from you knowledgable buffs!

I too have serious doubts about their 'bad' Ecu theory. And indeed, exhaust will not have any effect on that first sensor. IS the car actually using more fuel or running poorly? If they cleared the system with the install of a new sensor then the new code should tell them the source. If same code for front sensor not heating, despite change of that sensor, then I suspect a short in wires leading to that sensor.

Hi Brian, so good of you to reply

Well I agree with you entirely. Well, under normal driving conditions, the car feels pretty normal and runs fine, just sometimes when idling it feels and sounds like it's going to stall, like the revs are too low and the gear knob wobbles around violently.

They are claiming the new code is the same as the previous one, "front sensor". I can only wish it's a short in the wires, as such, I'll inspect it myself and pray to God that the worst that has happened is that one of the wires or your extension cable is burnt through. I'll keep you posted. Thank you

The header and lack of cat may cause the CEL. Did on mine on a somewhat irregular basis. The issue, as I understand it, is the cat in the header heats up the sensor and the ECU knows what to expect. With no front cat the ECU thinks there is a problem with the front Ox sensor not heating up properly and fires off a check engine light.

Just get a code reader and reset it. I used a scangauge. What code number is it setting off? It will be CEL PXXXXX.

See: http://forum.miata.net/vb/showthread.ph ... hlight=CEL

You can't just swap ECU, it is registered to the rest of the car's electronics and would need to be reloaded by Mazda with the proper program.

While sensor and wiring do seem much more likely, the PCM is still a possibility. The reason is that the current for the sensor heater is generated in, and controlled by, the PCM. Once the sensor is hot (from exhaust) it could still run fine, but if the PCM doesn't sense heater current during warm-up, it could still light the CEL. Could be a blown transistor inside, or something as simple as a broken connection.

Along the latter score, I'd suggest disconnecting and reconnecting both the sensor plug, and the PCM plugs. It's a long shot, but worth a try before going for the PCM.

jim

Hi guys i own a 1999 miata last week i got the old yellow light syndrome ArrrrAhhh my local friendly garage plugged her in and said top 0-2 sensor so $144 later i stuck one in and my local gurage reset the comp well lo an behold 21 miles later hello engine light so we plugged her in again . This time it says i need a new warmer cat this is a cal car with said emmission system So $480 bucks later and a fight to the finish the new cat and gaskets are on so we reset her again . 38 miles later here we go again so back to my local garage we go and plug her in again well guess what it tells me i need a new warmer cat and at this stage of the game i am very pissed So the situation is this Pay my local Mazda rip offs $100 to plug her in for five mins they tell me its the only way. but my question is this will they guarantee that there info is correct or am i being taken to the cleaners yet again . Could use some good advise right now thanks Aussie Ian

Hi guys.... damn, receuved Brians new o2 extension cables, have plugged them in, CEL was gone for like 5 minutes then came right back on again!!

Sloopercat, if I get a Scanguage, thatw ill only clear the engine light, it won't fix the issue.

If i put my foot down in the first say 10 minutes of driving, the car responds but almost coughs a few times and then the CEL starts flashing. Once exhaust is hot the car runs fine but CEL still shows up.

I can try unplugging PCM but I have no idea where it is or how to get to it. I love this car but am a complete novice when it comes to getting my hands dirty... if i knew what I was doing i'd be all over it by now.

I've had this issue for months. Someone said I should get my PCM checked and reconditioned/repaired, trouble is, there's no guarantee that will fix it and at AUD$600, i don't think i'm prepared to find out. I've spent a lot on this car, I love it, but this continous CEL is actually making me consider selling it!! Worst part is I don't want to, someone please help!!

your ECU sits directly underneath the stock airbox. Used examples can be found cheap on ebay, much less than the numbers you're getting quoted.

MXFIVE,

I've been running the GWR header with the stock midpipe and muffler for 15 months now and never had a CEL problem.

Now I was thinking, and I could be entirely wrong, if it is a heating problem in the first O2 sensor maybe your exhaust system is working too efficiently.

Rather than go to all that expense of a new/used ECU why not try and refit the OEM midpipe with new bung holes either side of the second CAT for the sensors and see if slowing down the gas flow slightly fixes the problem? The slower gas flow might heat the O2 sensor quicker after start up and avoid the CEL. Just a thought and I could be entirely wrong.

Hmmm...potentially still a wire issue...but right at the sensor. He now has the extension cables. If the wires going into the sensor get pinched over at hard angle where they enter the sensor it can cause the code. Make sure wires coming out of sensor are not folded over at hard angle...you want them coming straight out.

Hi Brian.
Yes, I have the cables, thank you, what I don't have here is YOU!! If you're in Melbourne soon, please, drop in
Regarding the pinching or wires coming out at an angle, may be a possibility, problem is my damn car is so low that even with a trolley jack under it it's still so tight and i can hardly move. That means each time i want something done, i go to Mazda (who in the words of Duke Nukem: tear me a new one) or go to my Auto Elec who is a great guy but it costs me every time.

Charlie Brown, I dont have the stock midpipe, it's a custom system front to back. GoodWin Headers, GoodWin midpipe and a custom quad muffler system from germany, so unfortunately i can't do a thing about using the stock midpipe

I'm seriously pulling what little hair i have left out, I'm so passionate about this car but it's amazing how seeing a CEL everyday drives you crazy. Each morning now, for the first, say 10 minutes, if i put the accelerator down it sort of coughs, seems as though once the engine/exhaust/o2 sensor?? is hot, it doesn't do it anymore.

As I have a BMC Carbon fibre CAI, I can clearly see what I think is the ECU, with all the coloured wires coming out. If I unplug it, leave for a minute or so and plug it all back in, will it reset everything or do anything positive?

I've also noticed that my battery terminals have a lot of umm crap around them, it's dusty powder, i clean it off but after a week or so, it's back.

If anyone is in Melbourne and can assist, please let me know.

Brian, if this was your car what would you do??

Thank you everyone, such a valuable resource you all are.

To reset the ECU, disconnect the negative battery terminal then press the brake pedal for a minute or two.

The fact that it coughs when cold means there is something not right....but I can't say from here what it is. Not sure what to suggest, but giving the dealer there the benefit of the doubt I would be tempted to get a junkyard ECU and give it a try to see if that makes any difference at all. As for what I would do.....I would consider having Joe at DPTUNE reflash my ECU to better optimize the fueling for better peak performance...and ask him to turn the light off while he is at it. I realize that is not nearly as convenient for somebody in Australia....but if you picked up an extra ECU anyway then you would not suffer any downtime.

I have the same problem in my NC for a long time.

This is not the wires because I check them in an expert lab. It is not the connector as he working perfectly.

This problem has started after I install the header. it causing by the different between the air temp in the sensor and the expected air temp as if there were CAT in the middle.

When the engine light is on - the computer is using the safe mode fuel program that is very rich - and the car have too much fuel, to little air and the performance is poor. you will fill it much more if you have tuned your car to optimum fuel program using the sniper.

What I am doing? I having code reader that deleting the codes - this is not the best solution but I go to a lot of export and no one could fix it.

Maybe if I will change the header to new one or to the original it will be OK. but I won't go to original again and to buy one more header + shipment to Israel will be too expensive.

Hmm, been there done that.
I bought new front & rear sensor's. There'er made by Bosch for Mazda, maybe by now one could buy from parts store not Mazda. Removed the RS header & installed OE header.
Lost some Zoom Zoom but I now have a full head of hair.
Good luck!