JaVq35hr

So my 2k2 6speed with a 2nd gen VQ has p0300 with no supporting codes. I've changed all coils and plugs, ran through my connections, added a second ground, and even tried unplugging each coil to see if i can target any specific cylinders and I've gotten no closer to resolving the issue. At this point besides doing a compression test and trying out new injectors I'm completely lost. I can't pass inspection without getting this fixed, does anyone have any ideas on what it could be???

Slamrod

iTrader: (11)

Is it running rough, or are you just getting the code? What brand of coils did you use for replacement? Are you using any sort of datalogging/diagnostic software? Any other symptoms other than the code itself? Did you do the swap yourself - are you sure all the correct parts were used and correct procedures done? When if ever was your MAF replaced?

Probably the most annoying code there is, lol.

JaVq35hr

Yes i did do the swap myself. Coils and plugs were just bought in a pack from Walmart in an effort to save money and simply diagnose the issue. Upon changing them there had been no changes from what was originally in the car prior. The car isn't running particularly rough but it definitely could be slightly better. There's no hesitation, struggle or heavy stumbling, she definitely pulls. Maf has been replaced in the past before about a year and a half or so by now. And my only insight to what's happening on the inside is the Torque bluetooth OBDII scanner

Child_uv_KoRn

iTrader: (7)

There's probably no way the coils that came with the engine (assuming OEM) were bad. And cheap aftermarket stuff will throw P0300 regardless of how it runs. I would put the original coils back and check the branding.

I assume you looked at everything close for vac leak, so I would be checking O2 sensor if so. In the case they're working fine, look at fuel trims, especially at idle. If it's adding fuel, then there must be a vac leak (technically could be bad injector...but if they're the new green ones, then I doubt it).

And is this a brand new swap or has it been fine for a while?

Slamrod

iTrader: (11)

I would suggest putting in OEM (Hitachi) coils. Aftermarket tends to have problems exactly like you are describing although its possible there are additional factors at play.

Could be a knock sensor issue? Possible for that to be it even without a specific knock sensor code. If youre willing to mess with your harness a little, you can wire in a resistor (550ohm IIRC, search the forums for “knock sensor bypass” or something like that to make sure) and that will rule out if that is part of the problem. I drove around for a long while with the resistor instead of a knock sensor but I would strongly recommend not doing that in case you get a bad tank of gas, or in my case, have some idiot at the gas station give you 87 octane instead of 93 like I asked for.

I promise it is not the electrical condenser on the harness either. It never is lol.

JaVq35hr

So i took up the advice soldered up a 550ohm resistor to a couple of leads and put that right into the knock sensor harness and no change (Lack of knock sensor code leads me to assume the bypass was successful). But at least it allowed me to narrow down the issue further.

I've been driving the car around attempting to clear some o2 codes but I believe that these problems are unrelated. after testing out the bypass i decided to finally get around to doing a compression test on the engine the values are

1- 150 psi
2- 180 psi
3- 150 psi
4- 185 psi
5- 130 psi***
6- 180 psi

Based on this I'm assuming cylinder 5 is the main issue. New rings might solve you think? Based on a wet test on the same cylinder it brought compression up to 150. The real kicker is that when doing the same test on cylinder 3 the value for that shot up to 180. So with that being said, is it time to pull out the engine AGAIN and get right to it? (cannot stress how many pulls I've done already) Or is there another quick fix I might be able to try just so I can pass inspection for the year?

Child_uv_KoRn

iTrader: (7)

Gap the plugs down and throw in some Restore. Those values are awful. I wonder what happened to that bank? That whole side is ****ed.

Unplug IVT solenoids and cam timing. Maybe that bank is off somehow, although I would expect a code for that, but maybe it's borderline.

JaVq35hr

I got the engine from an 09 maxima at a local junkyard, I guess the thing could've been through anything tbh. What exactly is restore? And what would I need to do? Just pull the plug and pour a bit in as if I was doing a wet compression test?

Child_uv_KoRn

iTrader: (7)

If the cylinders are ate up (very odd being one bank), then restore ups compression by filling in scratches. It goes in the oil.

But since that seems so odd, I would check timing first.

JaVq35hr

Okay so i figured I'd give that Engine Restore additive a try because of how inexpensive it is and i could already tell that the idle is much smoother it really feels like it's almost there. Casual driving feels okay and there's much less engine vibration by far. So i have a feeling that it helped a lot with whatever compression issues were there prior(will do a follow up compression test very soon).

The new problem:
P0300 is still here but followed up by a brand spanking new P0021 (is it wrong that I'm relieved to actually get another code?). The car has actually lost power from before, and it is very noticeable, doesn't nearly have the same pickup as before. With that being said I'm hoping that this means i can narrow it down to a sensor or 2 and run through the wiring with a multimeter. Any ideas of which sensor it could specifically be? Or if not any other fixes (taking a journey into romraider is an option as well perhaps?)

Child_uv_KoRn

iTrader: (7)

It'll clog the solenoid. I forgot to tell you to pour it in while the engine is running LOL. Spray it out.

You're going to have to check cam timing after cleaning the solenoid.

JaVq35hr

Oh wow... So you think the current fault is just because the solenoids are gummed up by this stuff now? When i spray it out you mean pull the solenoid and spray it with brake cleaner? And when i do this should i flush out the oil system to make sure this stuff is completely out and put in some fresh oil??

Child_uv_KoRn

iTrader: (7)

Just spray out the solenoid. It takes hundreds of miles for Restore to start working effectively (if there is indeed damage).

But that's why I said check the cam timing first...in the first place, ha.

JaVq35hr

Fair enough, you did say that 😅. I'll give it a try, hopefully i do just need to spray it down

JaVq35hr

Update: Pulled the bank 2 solenoid sprayed it down and moved the pin in and out by applying power through tiny alligator clips and a charged battery. P0021 is gone but p0300 is still here. I just pulled a p0430 code because my drive cycle has just been completed.
Current outlook: I'm gonna pull the plenum AGAIN and do another compression test to see if that fixed compression at all, if it did then I'll do a fuel pressure test since the tester finally came in the mail. If not then i guess I'm gonna have to pull the engine 😬

Questions: Would an exhaust leak cause or be related to p0300? If not would a bad precat do it and cause it to throw p0430 ontop of that? Also when looking at the fuel trims what should i be looking for in those values?

JaVq35hr

Side question: I've been looking for the exhaust manifold outlet bolts by the radiator side. Right on the flange that hooks up to the Cat. There's 6, including the front 2 threaded studs. Does anyone know where i can find these???