Need Help... Mazda 6 Misfire

[jmgtp]

I'm getting no where on the Mazda forums so I thought I'd give the expertise here a try.

info:
2004 Mazda 6s
83k miles
3L DOHC Duratec (yup, ford engine - and technically it is a 6/60)
5 speed manual

I get a P0301, misfire on #1, check engine light. Once the light is on it stays on. If I reset it, it comes back on ONLY when I reach 85 mph. And further to that condition it has to be in 5th gear, and maintaining or gently accelerating in the 85mph range. If I am in a lower gear, or accelerating hard in 5th, it will blow right past 85 and never see the CEL. If I simulate the rpm that it comes on at in 5th gear, in say 4th gear, I cannot get the CEL to trigger - needs to be 5th and needs to be in the 80-90mph range.

Once the light is on, exceeding 85 mph causes a flashing CEL indicating a severe misfire. Though, the engine runs smooth right through this and does not feel like anything is wrong in the slightest.

To date I have replaced all the spark plugs and all of the coil packs with new ones. I also swapped each fuel injector to another fuel injector position in hopes of getting the misfire code on a different cylinder and identifying the problem as a bad injector - clearly that didn't work because here I am with the same code indicating misfire #1.

So, with injectors, coils and plugs ruled out, what can be causing the misfire code on #1? It is REALLY strange that it only comes on under cruise conditions and can only be triggered in the 80-90 mph range. I'm really baffled as to what the problem can be. The wiring and connectors all look good and I cannot identify any vacuum leaks.

All of the o2 sensors are original at 83k. If they were bad could this cause a problem with fueling that would lead to a misfire? I imagine the computer would be smart enough to determine the o2 at fault and trigger a code for that though. It does get poor gas mileage, 18-20 mpg mixed, but I attribute that more to my right foot than anything else.

The car is all stock with the exception of a popular airbox mod and aftermarket motor/trans mounts.

Any input appreciated.

Thanks,
John

[bszopi]

Just don't drive in excess of 85mph.

[jmgtp]

haha... I was waiting for it, didn't think it'd be the very first response though! But that is one solution... how about some others?

[mazdacraze]

Hi John?

haha... I was waiting for it, didn't think it'd be the very first response though! But that is one solution... how about some others?

Dear John

I understand your frustration. I was very fortunate to get my cylinder 3 misfire problem resolved after a lot of frustration. I had changed my plugs and almost had to replace my fuel filter until we tested the leads by replacing them with others and off went the problem...just like that. If your lead wires have some white on the inside, it means they are the problem ones but you have to replace the entire set. I hope this helps you too and we can then spread the word that the Mazda6 is indeed a great car!

I would experience the same problem you have described at around 85-100kph and if I have to climb a very steep hill. Good luck John

[pocket-rocket]

Besides the post above mine, I would suggest O2 sensor change. At worst case you still have the CEL light (if you don't try the above posters advice), but you should gain some MPG and probably a little performance as well.

[86FieroSEv6]

One would hope that "John" had his problem resolved before now . . . . . (Apr '09) LOL

[pocket-rocket]

Good catch... I didn't even look at the post date.

[mazdacraze]

Good catch... I didn't even look at the post date.

I noted the date but set out looking to share a solution to what appears to be a common problem for which most Mazda forums do not address. It would be nice to know if the information were of use to someone else in a similar predicament.

[86FieroSEv6]

A truly laudable goal and not without merit. I would have to wonder why the Mazda forums don't seem to address misfire issues. I drive a ZX2 for my daily, which is a Mexican Mazda actually. I haven't had any 6's in for other than normal wear and tear and maintenance type stuff. No mysteries yet, anyway.

[pocket-rocket]

A truly laudable goal and not without merit. I would have to wonder why the Mazda forums don't seem to address misfire issues.

Most people with a SES light probably take the car to the dealers if they have the $$$ for a newer car. That's my guess anyways. BTW, mazdacraze, that is a noble act on your part since most people would have just carried on without so much as a thought to stop to lend a helping hand to someone.