After long drives, I get misfires and code po302 (rear rotor) misfire. I have new engine with only 5,000 miles on it along with new coils and plugs 5000 miles ago. Its a 2005 with 145,000 miles on it.

I took out spark plugs today from rear rotor and this is what they look like. Does anyone have any suggestions what can be causing po302 misfire? and also if these spark plugs look ok?

 

looks fine.

you might be running lean, any other code other than p0302 ?

 

Misfires can be caused by:
- Plugs
- Coils
- Wires
- e-shaft sensor
- MAF
- Vacuum leak
- Cat
- Compression loss
- Grounding problem
- Fuel injector clogging
- Fuel pump failing
- Bad gas
- Carbon caking

The plugs look pretty clean, definitely not overly rich. The next two quick and easy things to check are the e-shaft sensor and the MAF. Then vacuum leak if you have an ODB2 tool that can read live data.

"Long drives" could be an indicator of fuel pump issues...

 

Thanks for the quick responses guys! I have checked the e-shaft and cleaned it. How would I check the MAF sensor? I also have the OBD2 tool, but I don't know exactly how to review that for vacuum leaks.


No other codes than the Po302. I had a code for the park/neutral switch in the transmission 3 weeks ago - I took that sensor out and cleaned it, put it back in and never got the code again. Only the po302 at current.

 

edit --- damn those guys beat me to the post -- just forget this then

+1

Any modifications to the intake?

Clean Maf and ESS (plus ess reset) simple/easy/cheap way to start diagnosis

 

These are my 90K plugs. The car ran fine so yeah...keep working your way down the laundry list.

 

No modifications to the intake. Factory.

 

That square flat thing held into the top of your intake by 2 little screws? That's the back of the MAF sensor. Gently unscrew the screws, disconnect the electrical connector, pop it out by pulling up. Hose it down with a can of MAF cleaner from an autoparts store. Don't touch it, it's very sensitive to contamination. When replacing, screw it back in gently, since the screws can easily strip the intake threads.

If your ODB2 tool can see live data, fire up the car and let it come to a full warm steady state and watch the MAF and Short Term Fuel Trim (STFT). The MAF g/s should be around 5g/s at idle, and the STFT should be sitting at 0%, plus or minus 1%. If you have a vacuum leak, it means the engine is pulling are that the MAF isn't seeing, so the MAF data will drop (how much will be based on how big the leak is, it won't be more than ~1-1.5g/s) and the ECU won't be adding fuel automatically. However, the O2 sensor will see it running leaner than target, so the ECU will be trimming the fuel with STFT. A very slight leak can easily put the STFT into the +5-6% range, with a larger leak growing quickly more.

 

Ah I would just like to add -- becareful with the oring as well.

It's easy to get it pinched when reinstalling the Maf sensor.
More so with the metal after market intakes where it might actually get cut.

 

ok this is my cituation...put a re manufactured engine from mazda in my 05 RX8, mechanics got it running, but engine light pops on, apv motor bad replce apv motor no engine light...got it from mechanics drove for like 4 days engine light pops up code for front o2 sensor ok no big deal drove for a couple of days, went to start it to warm up, started up like normal idle fine then when i went to go get in it it was bogging out bad, thought maybe if i took it for a drive it would get better nope no power come to a stop it act likes it wants to die...car feeling up with smoke passenger side floor board really hot...have it towed to mechanic 2 codes pop up the 138 and 302...138 is for rear 02 sensor and 302 misfire...this is the kicker so what happen to the code for the front 02 sensor? lol....but when i test drove it the engine light was flashing instead of staying on...mechanic think that the cat converter is bad and that is probably causing misfire...went to go pick it up today but wouldnt start...they said they were driving it in and out of the shop so it was running...u think that the fuel pump could of went out also? but they said it ran out of gas at one point and had to put more in it...tell me what you think...thanks any advice could be helpful...

 

what was the outcome of your issue. I have the same problems with my car right now