Hello, Any input is welcome. Mileage is 116K miles. I installed new spark plugs (Denso FXE24HR11) 2K miles ago as routine maintenance along with air filters.
Recently the car started up a little rough in the morning but within a minute it smoothed out. This cycle continued for a few days so I plugged in a scanner and it came up with two codes P0300 and P0301. I replaced the coil and plug on the # 1 cylinder with a Hitachi 22448EY00A coil and Denso FXE24HR11. I'm not sure that made much of a difference in the symptom other than I now ONLY get a P0300 code. The P0301 code has not resurfaced. I'm inclined to replace the remaining coils (5) with new Hitachi coils and see if that solves the rough start and multiple misfires. If I clear the code using the scanner it resurfaces quickly P0300). Thoughts, suggestions, thanks!

If one coil was bad for sure, then the first thing you should do is a voltage-drop test on your block ground and the individual coil grounds. Bad grounding heats up the N-channel transistors inside COP coils and causes "warts" and eventual failures. When a whole rack of coils fail one after another, it's almost always a ground fault causing the issue. See this post for how to do voltage-drop (and why it's a good thing to know):

Keep your engine on the ground, not just the wheels!

If your grounds are healthy, on an '11, you may be able to read a misfire history out of the ECM with a good scanner. That will reveal if the remaining misfires are limited to a few cylinders or one bank, or are a generic issue like a vacuum leak.

VStar650CL, Thank you! Clear and concise. I hope to get to it this coming weekend. Also thanks for the excellent link about voltage drops.
Patrick

You're most welcome, keep us apprised.

I'm having the same issue the difference is I found what my problem is but don't know how to fix it, manual don't really specify or might of missed what I needed but I'm having a voltage drop at the injectors connector F10 and when I plug connector F102, I get the same voltage 9.5 but I believe it should be 12v. I've checked resistance on injectors getting ohms there at 13.5 can someone shine the lights and share with me what I'm missing or overlooking or what to do?

Voltage drop on the high side of the injector circuit can only come from the IPDM or the wiring. Note that the car must be running for all these tests, the circuit has to be loaded for voltage checks to mean anything:
1) Check both sides of F10:F120, if the F10 side is higher then you have a pin-fit or corrosion problem in the connector. If it's 9.5V on both sides...
2) Try disconnecting the Condenser at F8 and see if that makes a difference. If so replace the Condenser. If that makes no difference...
3) Check voltage at fuse #44 in the IPDM and pin 51 where the circuit comes out of the IPDM...
3a) If it's 9.5V at the fuse then you have a supply problem, probably a bad Ignition Relay or a problem on the IPDM circuit board, or...
3b) If it's 12V at the fuse but 9.5V at pin 51, pin 51 has a pin-fit problem or else the IPDM is definitely bad, or...
3c) If it's 12V at pin 51 then the wire between the IPDM and F10 is bad (high resistance)

VStar650CL thanks for your reply you seem pretty knowledgeable I read many post from you and I'm delighted with someone like you around. Do you know what should be the continuity of a good ignition coil as well as injectors? I believe I do have 12v to the harness when I plug the multimeter red to the green wire to connector and the black on ground. I appreciate your help whatever you can give. By the way all the pointers you threw out I have already checked out but I appreciate the help.

Danbam wrote: ↑

Sun Jul 10, 2022 9:51 pm

VStar650CL thanks for your reply you seem pretty knowledgeable I read many post from you and I'm delighted with someone like you around. Do you know what should be the continuity of a good ignition coil as well as injectors?

You're most welcome, happy to help. Checking Nissan COP coils with an ohmmeter is pretty much a useless exercise, because you can only check the secondary coil and it tells you nothing about the condition of the primary or the driver FET. The latter are what usually fail and not the coil windings. For misses on individual coils, the best test is to swap cylinders and see if the P030x moves along with the coil. For a general check, use a spark tester and make sure it's throwing a healthy purple spark at least 3/4" or so.

Danbam wrote: ↑

Sun Jul 10, 2022 9:51 pm

I believe I do have 12v to the harness when I plug the multimeter red to the green wire to connector and the black on ground.

If there's 12V at the pin on F10 but 9.5V at the same pin on F120, that's a smoking gun, the connector pins are bad. It's either corrosion or a bad pin-fit. If it isn't corroded, then the female pin may have a broken spring or a spring that's simply too weak to maintain good contact. Either way, the fix is to replace the female pin (or the whole female connector) with a pigtail.

Ok, I'll definitely will check that out. Thank you for your help.

Hey, any updates? having same problem had P0300 and P0304, changed ignition coils, P0304 turned off and just P0300 comes on, it starts fine so I don’t think it’s the injectors, there was a little oil in the 1st cylinder spark plug and ignition coil, took a rag and cleaned the oil out, but still not sure what the problem could be