My car has been acting unusual lately and I am at a loss.

I have a IX GSR and have been having a recent issue with the P0300 code and multiple random misfires. The car will run fine, then drop and run on two cylinders. I have set the periphery bits to deactivate the code but am still having drivability issues so I know that it is a real misfire issue. It will self-correct and return to normal as it feels so appropriate but that doesn’t make diagnosing the issue easy.

I am running a COP and have swapped coils, changed plugs and that has not resolved the issue. The problem stays with cylinders 2-3 from what I can tell. I can recreate the engine condition by pulling the plug on the passenger coil connector.

Has anyone else encountered a similar issue? I will probably be pulling apart my COP wiring to make sure I don’t have an issue there but I am stumped as to what else it could be?

My only other thought is low battery voltage maybe?

 

I would bet heavy money on COP wiring. I had a very similar issue and found issues with the harness I had.
Made a new harness and all my issues went away.

 

If you're having a misfire on coils 2 & 3, it's likely the wire harness has some loose pins since those two coils are powered by the same gray connector that plugs into your factory harness. Check the pins inside the connector and make sure all three are solid and not loose when you push them in. If you do find a loose pin, you may be able to pull it back into place unless the pin lock is broken.

 

I just spent a lot of time diagnosing my no-start issue, so now I will always recommend to check the timing belt. check if it skipped

 

Just pulled the harness off of the car. I confirmed continuity and acceptable resistance for both plugs (2-3).

I agree that it is likely an electrical issue with the plug, but everything appears in order. I’m half tempted to put a tiny bit of dielectric grease on the pins.

Is there a good (read easy) way to test the car side of the harness?

 

Using dielectric grease is never a bad idea to reduce corrosion and increase continuity with the pins. The only way I could think to test the car's factory harness is to use a multimeter on the pins and see if you get the correct power reading while the car is being started. I've never heard of a car's factory ignition harness going bad and there's only one fuse that powers both of the factory connectors. If the fuse blows, you won't have any power to the ignition system at all. If you can replicate the issue by pulling the connector off the passenger side, it leads me to think it may be a pin not making a steady connection. If you have one of our JDC cop kits, our wire harnesses come with a lifetime warranty. If it's another brand you may be able to reach out for a replacement under warranty.

 

For mine, I found issues when flexing the wiring, it had broke inside the coating but generally measured in spec when left alone.

Might be worth doing a more through(read rough lol) test of the harness. That thing sees a fair bit of vibration and stuff that can cause issues like this to be hard to diagnose.

 

Points to Schuhie! Grounding pin on the harness plug was pushed back a bit off the plug and wasn’t making solid contact. Gave it a good tug and added some dielectric grease and she runs like a monster again.

I’ll order a new plug since it appears the retainers aren’t holding the pins in place, but I may just zip tie the wires and make a strap to hold them forward. All is well in the world now!

Thank you everyone!

 

I put some glue on one of my terminals. after a red wire broke i had to redo the crimp but it wont lock in anymore