Cats were replaced!

I just changed out my spark plugs, PCV valve, and air filter for a tuneup. Now I'm getting a P0300 code. Anyone have any additional troubleshooting ideas?

Here's the sequence of events:
1) Removed intake
2) cleaned TB
3) Removed spark plugs and changed PCV valve
4) Did a compression check #4 was lowest at 130 #1 highest at 160, rest were ~140-145, all at three strokes
5) Installed plugs
+) Wired up #4 and 6 backwards (did not find out till later)
6) installed intake
7) started up and ran like shart immediately
8) removed intake, found and fixed #4+6
9) installed intake, started up and ran noticeably better but with a louder exhaust noise then normal
10) took a quick drive and got the P0300 code with noticeable power loss
11) disconnected intake and tweaked the gap on the plugs
12) Cleaned the MAF and installed old PCV
13) reconnected everything
14) Started it up and still had louder exhaust noise
+) Checked for vacuum leaks - OK
15) took a drive and same P0300

Every time I take it for a drive I reset the codes. Shortly down the road the check engine light blinks but then disappears when I idle. The FSM says this is caused by excessive fuel going to the CAT. Also, if I reset the codes and just let it idle for about 10 minutes no new codes will come up.

Today so far I've done the following.

-) Let car sit with battery unplugged over night
-) Check ignition coils resistance - OK
-) Took out new plugs - #2, 4, & 6 now have carbon buildup

The carbon buildup on the drivers side bank disturbs me. I looked at the old plugs and they don't have this. Could I have f-ed up the whole bank somehow (versus just injectors 4 and 6)? Or does this just happen when sitting at an idle for a while?

The old plugs were in okay shape. They all look like they've been run hot with a little wear on all of them. I'm going to slap them back in but I'm not going to expect this to fix anything.

I've ZERO engine mods to speak of.

 

Don’t know if this will help but here is some additional information and ideas on what to check. Based on what you have already re-done:

Items to check:
* check for intake air leak and PCV hose leak -(most likely since a lean condition will result in a different sounding exhaust note)
* system clogging - visually check exhaust tube, three way catalyst and muffler for dents. (not likely since you didn't do anything here)
* check function of ignition coils (not likely that more than one is damaged and the 0300 code indicates issues with multiple cylinders)

Possible causes:
- Improper spark plug
- Insufficient compression
- Incorrect fuel pressure
- The fuel injector circuit is open or shorted
- Fuel injector
- Intake air leak
- The ignition signal circuit is open or shorted
- Lack of fuel
- Signal plate
- Air fuel ratio (A/F) sensor
- Incorrect PCV hose connection

Good luck. It’s really frustrating when you perform maintenance to improve things you get bad results.

 

i am having the same problem with the p0300 code and exhaust sounding funky. I haven't had time to diagnose it yet, but from my reading it seems there are four somewhat common causes for this on the Z.
1) ignition coil pack
2) spark plug
3) maf sensor
4) fuel injector

I also believe I had read that even if there is a single cylinder misfire, the code won't always be specific to that cylinder. So just because your car is throwing the P0300 instead of a cylinder specific code, doesn't mean you have a multiple cylinder misfire. I would start (will start on my car) by checking the MAF, then coil packs and injectors, and last the fuel injectors. I see this path as the easiest route for testing.

And let us know what you find to solve your problem.

 

I haven't been pulling a MAF code and I did clean it. But I'll go ahead and check resistance on it because it's not that hard. I honestly think I messed up the injectors somehow. I really didn't want to take the plenum off but it's not that hard I guess.

I wish I has a cypher to diagnose all this crap easier.

 

- Ignition coil pack - Checked OK
- Spark plug - Checked OK
- MAF sensor - Checked OK
- Fuel injector - Working on Checking
- Insufficient compression - Checked OK
- Incorrect fuel pressure -
- The fuel injector circuit is open or shorted -
- Intake air leak - Checked OK
- The ignition signal circuit is open or shorted
- Lack of fuel - Checked OK
- Signal plate - ???
- Air fuel ratio (A/F) sensor -
- Incorrect PCV hose connection - Checked OK

I checked all the injectors for functionality and resistance, they were all okay. Is there a way to tell if one or more is dirt/clogged?

 

not to insult your intelligence but look at the wiring to the coils. It's VERY common for people to hook the wrong wires to the wrong coils causing misfire.

also, mine had one of the wires to one of the injectors loose in the connector which was causing a poor connection. This can also happen on the coil pack connectors. Check each individual wire on each coil and injector to make sure none of them have come loose.

 

From 1st post.
But thanks for the reply.

And I checked to make sure the connections are tight. The coils are working properly. I think crossing them is what started this shat.

 

Platinum or Iridium plugs? Intake manifold torqued to spec and sequence?

 

I purchased the exact NGK's as recommended by the FSM. They are the Platinum ones. At first I didn't check the gap because the FSM says not to, but the next time I took them out I gaped them to spec without change to the p0300 code.

And I never took off the manifold until I removed the injectors, so I can't comment on the torque. But once it goes back on It'll get the proper torque, I have a 3/8" torque wrench.

I'm going to get the injectors cleaned and tested this week. Sucks I have to wait 'till next Friday to do it because I'm too busy at work during the week. Unless I start feeling sick...

Edit:

If the injectors don't fix it the G is going to Infiniti, and I'll receive some good rape-age in the wallet.

 

I get the same code from time to time and went through everything as well. Came down to being bad gas ::shrug::

 

You could buy a scanner that reads your datastream and does power balance testing for what the dealership will charge you in diagnostics.

With the engine running start unplugging the coilpacks in sequence and see if any cylinder is weak compared to others. Make sure and run the engine normal a bit between tests to keeps the cats from saturation.

I really doubt you messed up your injectors, I've broken lots of things and seen them broken working on cars but never injectors. Plus ECM is pretty good at seeing injector fault.

 

you checked each individual wire inside the connector? my connectors were all snapped perfectly tight but i had 1 wire that backed out of the connector itself. Took me a month of re-checking and unhooking connectors and rehooking them before finally on accident i grabbed one and the wire pulled out. Adjusted the tab on the metal connector, pressed it back in, problem solved instantly.

Those are on the injector harness but i guess the same thing could happen on the coil plugs. Since it's a whole bank that is having issues (carbon) i would look further up the wiring harness chain to see if something might have come loose on accident up there.

 

I checked the connections. The coils were all tight. And I function tested the injectors at the harness behind the engine so they are also good.

I didn't see this before I took the manifold off but the hose that runs from the Rocker Cover to just upstream of the TB has oil on and around it at the connection to the rocker cover. So this could be 60000 miles of build up or a weeks worth of troubleshooting. I just wiped it off so the picture doesn't show the buildup. It wasn't very much but it was still liquid.

Edit: Now that I think about it there was oil buildup on the TB the very first time I took the intake off. So I'd guess that was 60000 miles worth of buildup.

 

Is cranking time still normal? And does your scan tool show freeze frames for the codes? Starting to sound like CMP problem.

 

I don't know what CMP is and No I have a cheep-o OBD-II Scanner.

 

Camshaft position sensor, back of head, looks like you have it unplugged in that pic. Will cause hard starting, stalling and it is how the ECM would determine which cylinder would be misfiring.

 

Oh that was deliberate. That Gray/Orange plug in the bottom left of the photo is the fuel injector harness. The gray plug in the center is for the TB. Everything else is plugged in tight in the photo. Perhaps it's just the angle of the shot.

 

Was just to give reference point. When mine went bad the car first randomly stalled with no one in it(on Autox grid; confusing!), then took 2x cranking time with louder exhaust and misfire codes; eventually set CMP related code.

It's very common, there's a thread or two every week that is probably caused by one going bad.

 

I just had the plenum removed, checked for flow from the injectors and hung each ignition coil with a grounded plug to make sure everything is firing. Everything I check is okay.

I only ever get the p0300 code, no indication of a CPS code or a specific cylinder.

The last thing I think I'm going to try this weekend is pull each ignition coil harness while the car is running and see if i can narrow it down, even though I know they all work.

This is likely going into the stealership next week, unless someone's got some other suggestions I can try.

I don't suppose something like this is covered under the powertrain warranty? I'm going to have to do some reading.

 

Some additional info. When driving under mid or low throttle you can easily tell from the exhaust note something is wrong. Under WOT I can notice individual misfires and occasional step changes in power.