Blinking CEL and *better* gaz mileage??
 

Hi there, I wanted to post in troubleshooting but I'm still too new.

All was good in renesis land till last week. I got blinking CEL, which is misfire. It happens at 7700 RPM and up, only on load (revving while standing still does not trigger it). Also, it takes a second or two after I shift for the CEL to start blinking. And I must trigger it 3 times in a driving session for a solid CEL to come up. Otherwise, nothing is logged in the ECU. The CEL I get is P0302, Misfire cylinder 2 (rear rotor).

Now the weird part is, it's my best tank ever. I had the car for 8 month, 3K miles. Mileage is about 20% better. I was doing 220 miles max. I'm now at 190 miles and I have a quarter tank left. So I should easily do 250-260 miles, which is unheard of for my car. And my butt dyno says it pulls a lot better too. I was wondering if compression was coming up and tested it with a piston tester, but no, it's not up.

So far, I read all sort of posts, and the "Misfire, Start here" post. I checked the following:

Coils, plugs, wires and air filter are 3k miles old. Compression was taken right after I got the car (bad move), 81-83 psi at 250 RPM. Still at the same compression now. No starting problem to date. Rear rotor has sligthly higher compression (84-85. I premix JASO FD synth oil, 275 ml per tank (9.2oz).

Swaped the coil to see if problem changed rotor, no joy
Swaped the plugs to see if problem changed rotor, no joy
Reseated all wires, both ends, no joy
Re-Cleaned MAF, no joy
Re-Cleand ESS, no joy
Cleared NVRAM (ESS profile), no joy
Changed engine oil (was due anyway), no joy
Checked oil in air filter, no joy
Checked loose vaccum hose, no joy
Cleaned throttle body, no joy

Now, what I don't get is why mileage and power would go up instead of down if misfiring.

Next steps are disconnecting the CAT to see if it's ok. Would a failing fuel pump or injector cause mileage and power to go up as well as misfires?

Thanks for inputs!

Since you've already done this much im going to suggest something else. I noticed you reseated all of your plug wires. Have you checked your connections at the coil harness as well? Did you make sure that all of those wires are seated properly and clean from dirt? Have you checked your o2 sensor?

Misfires are usually coils, plugs or wires but, they can be caused by a whole host of things.

https://www.rx8club.com/series-i-tec...isfire-242973/
https://www.rx8club.com/series-i-tro...2-here-122318/

If i were you i would go through this thread again. Step by step and check everything off, im sure there is something you missed.
https://www.rx8club.com/series-i-tec...t-here-222280/


Go through this as well.
https://www.rx8club.com/series-i-tro...memory-169443/

Once your finished come back and post your results and we shall go from there.

85psi ? that's a failed. your engine is bad.

and yep, ur symptom is exactly what a failed engine does.

Yes, I agree it is sub Mazda specs by a good margin. No doubt about that. However, it was'nt misfiring for the last 3k miles, even with one failed coil on front rotor (when I got it). It was running like crap, but no misfire whatsoever.

My question is not only about misfire, but also about the better fuel mileage. They appeared togheter and it's suspect to me.

So I'd rather look everywhere else 1st before spending 3k and a lot of trouble.

Thanks, some links I have'nt read yet. Will look into that!

Possible one of your seal is gone already.
Less friction between rotor and housing causing the rotation out of rhythm.

Well, thanks to all who contributed. I unpluged negative battery terminal this morning for about ½ hours (had time ahead of me). Also had a can of injector cleaner you put in the gaz (STP, if one wants to know). I put it in. I don't believe a lot in those, but I had one laying around (was quite dusty lol), why not try it. Then I went to drive a bit. No more blinking CEL!

IIRC, last fillup I did put a bit more premix, maybe it fooled the PCM, I don't know.

Anyway, it's all good for now.

Thanks again!