Hello everyone, let me preface this by saying yes, I already searched. Lots of people making threads with this but never posed their resolution or identified what the problem was. I'm stumped and need help. I will make this post and sleep on it, hoping to come back at it with a clear head tomorrow with fresh ideas from you all.

2006 sedan 5at, 103.5k on the clock. Drove car up onto ramps (tried jack/stands, freaked me out. That's for a different thread), changed oil, filled up with 5 qts, engine fired up immediately and ran smooth (Mobil 1 0-40 euro spec with Mobil 1 M1-110 filter as recommended per this site). I let it run for about a minute to make sure oil was circulating and no oil was leaking from the drain plug/filter. Shut everything down and started working on the plugs.

Did driver side first, front to back, using the OEM factory recommended replacement plugs with anti-seize. No major issues there as I followed the DYI posted on this site (thanks). Then I started working on the passenger side, back to front. Back passenger side has the telltale signs of oil starting to seep but isn't bad enough to drench the plug, yet. So I figured it was OK to continue on while I figured out my options. Passenger center plug removal went well. After I replaced the passenger center plug and reinstalled the coil, I grabbed the wrong torque wrench (set for 20 ft. lbs for spark plug) and cranked down on the coil bolt, wondering why it was taking so much. Caught my mistake when I looked at the torque wrench and attempted to back out bolt, which proceeded to snap off. Used an extractor and got the bolt out easily as it was loose. I figured I could use a bolt that held one of the wire harness brackets to hold the coil in place while I waited for a replacement. Torqued it down correctly. Did passenger front without issues and reconnected everything, or so I thought.

Attempted to start the car and there was a pop sound so I stopped. Looked around and noticed that I forgot to reconnect 2 hoses that led to the plenum, 1 on the side and 1 on the front to the side. I tried to get the front one back on and the hose split (really short, it was rock hard). I super glued it and then put electrical tape on it to give it a temporary seal while I sourced a replacement. Put it back on and went to fire it up. Car fired up but took a couple of attempts, and then ran really rough and idled horribly. I shut it down and checked the coils, found that the passenger front coil plug was not securely connected so I corrected that. Tried again and car fired right up, idled better but still rough, then got the CEL. Shut everything down and pulled the code, it was the dreaded P0300 code. Checked everything again, searched the forums, checked the car again, discovered that the middle passenger coil had come lose due to the replacement bolt being too short. Fixed it, cleared ECU, cleared code and fired up the engine again. No change, still got CEL, P0300. I've checked all the coils and connectors to make sure everything was secure, no wires broken, etc. I'm seriously stumped!

What do I do now? How do I tell if a coil is bad and which one? My understanding is that the OBD would give you a code that's specific to the cylinder but I only get the P0300. If I let the engine run after the CEL appears, the CEL starts flashing. A sidenote: While cleaning off the coils (dust, etc), I noticed that the stalks had some movement compared to the base, but none of the rubber was cracked or broken. Are the coils and stalks 1 piece or two piece?

Any ideas, suggestions, or advice? I'm pretty tech-savvy and can troubleshoot my way through most common problems. But I'm stuck. Any help would be greatly appreciated. Thanks!

 

my guess is you broke the coil you tried to over tighten and possibly it is arcing.

 

I thought of that possibility but ruled it out as I'm not getting a specific cylinder code. Swapping coils also doesn't seem to make any difference or give a specific cylinder misfire code.

Here's an update: I combed through the FSM and spotted on page EM-20 under Intake Manifold Collector, part number 11 is the PCV hose that goes directly to the PCV valve. This was the hose that I split. Went ahead and replaced this, still no dice. However the situation has improved somewhat.

While I'm still getting the rough idle and the P0300 code along with loss of power and hesitation, the CEL will come on, blink, and then go off, then repeats after a small period of time. This is different from before where it would come on, blink, and then stay on while remaining solid. I'm not sure what this means, if anything.

Local autozone guys are adamant that it's a leak in the intake hoses somewhere. I cleaned out the OEM filter and resued it but it was pretty bad. Could this be part of the problem? If you think I should replace the airfilter, I'll go ahead and do so. I just wanted to wait for my z-tube to arrive.

Should I reset the ECU? I'll put the intake back together and test it for leaks but I'm running out of ideas. Should I safely assume that the coils/plugs are fine since I'm not getting a cylinder specific misfire code?

Edit: Another possibility is I could have swapped one of the coil connectors to the wrong plugs. Could this be part of the P0300 problem or would that throw a specific cylinder misfire code? The identification tags have all fallen off. How do I verify which connector goes to which plug/coil?

 

Upon further searching, inspection, and combing through the forums, I found this: https://g35driver.com/forums/engine-...ml#post5053164

More specifically, I had plug wires #4 and #6 switched as noted via the red tracer wire. Other than that, they are literally identical, right down to how the wires curve to the connection from the factory.

Switched #4 and #6 according to the red tracer wire for #6. Fired up the car and it immediately fired and idled smooth. No CEL, no idle stumble, etc. Took it out for a cautionary brief drive, no CEL, no loss of power, etc. Shut everything down and checked codes, still had the P0300 code (pending), cleared it and fired it up again. After confirming that Idle was correct, smooth, and no CEL popped, I took it out and drove it hard. Car didn't miss a beat and gave renewed power due to the new plugs. After about 5 minutes of hard driving, I pulled over and checked for codes again. Everything came back clear!

I can safely assume that the culprit was the #4 and #6 coil connectors being switched. This solved my P0300 code.

 

I love happy endings

 

I was just about to suggest that the wires were switched. IIRC they come out of the same tape-out on the harness. Very easy to mix these up so I always recommend anyone doing plugs or coils to do them one at a time to avoid this issue.

 

You can on the passenger side, even though there's less room to work with. On the driver's side, you have to disconnect the #4 and #6 in order to move the harness out of the way enough to clear the coil as you remove it. Plus I had to be extra careful due the Arizona heat drying everything out and things disintegrating at my mere touch.

I agree though, extremely easy to mix up. I wonder how many P0300 codes reported here after spark plug changes were due to #4 and #6 being replaced.

If nothing else, I hope that this helps someone else later on down the road

 

Quite a few. I remember a few years ago when a ton of cars were around 100K miles there were plenty of threads resulting from the mixing up of the coil wiring. Was common enough that that's what I instantly thought of

 

Good to know. Hopefully it helps in the future.

Another update: had a P0430 code thrown this morning. UGH. Pulled it and it's related to bank #2, cyl 2, 4, and 6. I wonder if it has to do with the coil mix-up and resulting unbunt gas through the system. Although it's been a day now. I didn't reset the ecu after discovering my mistake so I'm going to clear the code, reset the ECU, and then have my wife continue to drive it and see if it pops up again.

 

Hmmm, I updated this once before but it didn't hold for whatever reason.

I reset the ECU and cleared the code yesterday (01/07/2016). Code came back again today. Not sure what to do about it and there really isn't any answer on the forums, atleast not one that I've seen. Gonna keep clearing it over the next few days and see if it eventually goes away. If not, I'll have to take it do the dealership and let them go through the diagnostic procedures.

 

According to AllDataDIY the P0430 is related to the catalytic A/F sensor or catalytic converter.

Could be caused by exhaust leaks, intake air leaks, fuel injectors, spark plugs, or ignition coils 1-3. I'd start with intake leaks, since you had those parts off.

 

It's actually coils 2, 4, 6. That's bank 2.

I honestly thought the intake could have been possible, but wouldn't that then also throw the P0420 for bank 1 as well?

 

http://www.nicoclub.com/FSM/G35/Seda...5_Sedan/ec.pdf

Page 395-400 gives you some things to check.


P0420 is bank 1
P0430 is bank 2

 

You guys are right, I was just summarizing what I saw on AllData and it had the ignition coils I listed.

Not necessarily, I kept getting a lean code that I could not track down for the life of me. It was also occurring only on bank 1. It ended up being the o-ring behind the brake booster causing the problem. So, even though extra air was getting in the system only one side was affected.

I only tracked down that vacuum leak after building a DIY smoke machine.

I used SeaFoam to check for exhaust leaks.

I have read on a few sites though that usually when you get a P0430 or P0420 code it means that actual CAT is fubared.

I'd double check your work on that side also. Take the spark plugs back out, reseat connections, etc..

 

This P0430 code is driving me crazy!

Fixing to take it to a dealer and pay through the nose to have them officially "diagnose" the problem. I doubt they'll actually do the cats/O2 sensor testing. How do I verify that they actually do?

Gonna wait for some feedback and look it over again before I take it in. When I clear the code, it takes 1-2 days for it to come back. Anywhere from 25-60 miles. I KNOW it's not the cat.

One thing I've noticed is that sometimes the idle will slow down while at a stop and it'll drop to 650ish and hold there.I can feel the weird idle change, almost like a misfire, and then it drops and idles smoothly again. Not sure if it's related or what that could be.

Will post more as soon as I have any new developments. Meanwhile, looking for a Z-tube. I wonder if I might have broken the G tube. I've gotten a bit rough with putting it in/taking it out in frustration a few times.