P0303 Code - Cylinder 3 misfire

[Chomperr]

Hello, I have a 2018 GT automatic, 16.3k miles, basically stock except for a Catback exhaust.

CEL popped P0303 code for cylinder 3 misfire at around 15.5k miles. I changed the spark plugs on Cylinders 1-3-5-7 and tested all the coil packs for voltage with a tester everything good. I thought maybe I got some bad gas so I threw in some octane booster, I always fill up with 91 (no 93 in my region) Cleared the code.

Drove to LA this weekend about 800 miles round trip, fun drive but CEL popped up again at about the 600 mile mark on my way back home. The odd thing is I don’t notice the car behaving or performing any different than normal, it drives great imo but I’m afraid to keep driving with a CEL on. This car is my daily so I don’t drive like a maniac besides the occasional pull on open road.

Anyone else ever have this issue? With the performance seeming unaffected I’m wondering if the issue is somewhat benign? I don’t know what else it could be. My warranty is expired.

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[WCRookie99]

Double check that your O2 sensors on that side are tight. Same with plugs. Would be the quick fix.

 

[Chomperr]

Double check that your O2 sensors on that side are tight. Same with plugs. Would be the quick fix.

I’m not the most mechanically inclined but why would the O2 sensor affect that cylinder specifically?

The first time the code popped, the night before, I hit a dip too fast and it scraped a little. Maybe something got knocked loose? I’m lowered on springs.

 

[WCRookie99]

I’m not the most mechanically inclined but why would the O2 sensor affect that cylinder specifically?

The first time the code popped, the night before, I hit a dip too fast and it scraped a little. Maybe something got knocked loose? I’m lowered on springs.

All I know is, my O2 sensor actually backed out from being trailer 8,000 miles (obviously not ever fully tight when Headers were installed). Poped that code plus the O2 code, I put the O2 back in and never happened again.

 

[Chomperr]

Update: checked code and now it’s P0304- cyl4 misfire. Before it was only cylinder 3. All we did was changed the plugs. No clue what’s going on.

 

[Chomperr]

Decided to replace the entire intake manifold and cleared code. If it comes back after this then I’m at a loss.

 

[Cobra Jet]

Next time it happens and if it is a specific cylinder code, swap the adjacent coil pack, clear the code and see if the code “follows” the coil pack. If it did, culprit is a failing coil pack.

Also do wiggle test and make sure all connectors to coil packs are 100% secure as well as any other Eire harnesses in the vicinity.

 

[Chomperr]

Next time it happens and if it is a specific cylinder code, swap the adjacent coil pack, clear the code and see if the code “follows” the coil pack. If it did, culprit is a failing coil pack.

Also do wiggle test and make sure all connectors to coil packs are 100% secure as well as any other Eire harnesses in the vicinity.

Will try that next time as we overlooked it after we tested each one. We also changed all the injectors just to be safe. New manifold on and everything was checked and tightened. I feel like accelleration is a lot smoother after the mani swap but it could be all in my head.

I don’t understand how it went from throwing a code for #3 (misfire) to #4 on the second occurrence after driving several hundred miles. Both on the passenger side bay.

 

[NGOT8R]

I had P0300, 0303, 0304 and 0307 pop up on my car (manual tranny). Did a crank relearn and so far, they haven’t returned.

 

[Chomperr]

I had P0300, 0303, 0304 and 0307 pop up on my car (manual tranny). Did a crank relearn and so far, they haven’t returned.

Yeah my digging around in old threads with similar issues seemed to be either manuals or Ecoboosts or 15-17’s. I remember their being a crank re-learn option on my old tuner for my previous Mustang. What exactly does it do?

 

[NGOT8R]

Yeah my digging around in old threads with similar issues seemed to be either manuals or Ecoboosts or 15-17’s. I remember their being a crank re-learn option on my old tuner for my previous Mustang. What exactly does it do?

I did mine using my nGauge after receiving misfire codes following a clutch install.

Have a look here for more information:

https://ngksparkplugs.com/wp-conten...sSmarts-Position-Sensor-Cam-Crank-Relearn.pdf

 

[NGOT8R]

I should also mention that while my clutch was out of the car, I installed a new crank sensor and trigger wheel. I wasn’t having trouble out of the original ones, but I figured that since I was right there and had easy access to them, it made sense to change them.

I would probably follow this same train of thought whenever I have to replace a clutch In the future

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