P0300 Code

Hey so I’ve got a 2006 Nissan 350Z with a regular low milage DE engine swapped into it. Currently having a P0300 code and I’ve done coil packs spark plugs valve covers and gaskets. Absolutely clueless at this point. Only code is the p0300 so idk what to do. Dokt have access to any real good scan tools. Just the one at oreilys. Anything helps. Email @kaleb402211@icloud.com thank you!

Kaleb, can you feel a misfire with the engine idling? Or, while driving down the road?

If it's a misfire at idle, you can start with a power balance test to narrow down which cylinder is misfiring.

If you're depending on the folks at Slow'Reillys for your scanning tasks, you probably better off getting BlueDriver or the like. Save you trips, plus more/better diagnostic data.

Hey Tyler, so I feel a misfire pretty much everywhere. Can hear and feel at idle aswell as when driving. Almost feels like the car is “stalling” as certain rpm’s or trying to do a really bad two step lmao. Only time it doesn’t feel like it’s misfire is when I’m getting on it but I can feel that theirs not as much power as before.

Injector stuck open, pull the plugs and look for a wet one. The fuel from the stuck injector will back-flow into the other cylinders in the intake plenum. You may be able to tap all the injectors to see if you can get it to close but the real solution will be to replace. Mileage?

35-45 k. Imported from Japan so coulda been sitting a while

Kaleb wrote:

Hey Tyler, so I feel a misfire pretty much everywhere. Can hear and feel at idle aswell as when driving. Almost feels like the car is “stalling” as certain rpm’s or trying to do a really bad two step lmao. Only time it doesn’t feel like it’s misfire is when I’m getting on it but I can feel that theirs not as much power as before.

That sounds pretty much like a constant misfire. Which, as far as diagnostics go, makes you job easier. 

Start with a power balance test. With the engine idling, disconnect one ignition coil at a time. If you disconnect a coil and the engine runs worse, that cylinder is contributing. Move on down the line. If you disconnect a coil and the way the engine runs doesn't change, you've found a misfiring cylinder.

Do this test on all six cylinders. If you're uncertain about the results, don't hesitate to it a few times. Just don't leave one unplugged and create more misfires!

Once you know which cylinder is misfiring, you can decide on your next test.

So basically one at a time disconnect each coil until I find one that doesn’t change the way the engine runs? What if they all make it change or what if none of them change?

Kaleb wrote:

So basically one at a time disconnect each coil until I find one that doesn’t change the way the engine runs? What if they all make it change or what if none of them change?

That's the idea!

If they all change, then it's possible the misfire wasn't happening when you did the test. Not a big deal, just means we'd go on to another test.

If none change, then we'd have to wonder how the engine is running at all.   It's possible that all cylinders wouldn't have very much change, which might indicate something common to all cylinders. 

When I did valve covers I took a look at the intake valves and the rockers and everything and it seemed like a really healthy engine (atleast top end) so fingers crossed theirs nothing seriously wrong. Any way to test injectors if just disconnecting coil packs doesn’t bring results?

Kaleb wrote:

When I did valve covers I took a look at the intake valves and the rockers and everything and it seemed like a really healthy engine (atleast top end) so fingers crossed theirs nothing seriously wrong. Any way to test injectors if just disconnecting coil packs doesn’t bring results?

There are several ways to test injectors, but I don't want to jump ahead just yet. Lets ID the cylinder that's misfiring first.

To be clear about the power balance test: The only thing it tells you is if a cylinder isn't contributing (misfiring). It does not tell you why. For example, if you disconnected the #1 coil and found no change to the way the engine ran, that'd indicate #1 is misfiring. That would still leave injector, ignition or mechanical on the table.

Gotcha. Well tomorrow I’ll get right on that. I did coil packs spark plugs gaskets and valve covers so I think all that would remain would be injectors but I’ll see what I can figure out. Thank you! Let you know asap

So I unplugged each one one at a time and it sounded worse each time. Idk what the rly means.

If you can hear a change in how the engine runs when you disconnect each injector, it means that each injector is working to some extent. Have you checked compression? Try doing a clear flood mode crank and listen to the cadence of the engine as it rotates. It should sound even. If it doesn't, I could indicate a compression problem.

Kaleb wrote:

So I unplugged each one one at a time and it sounded worse each time. Idk what the rly means.

That just means the misfire wasn't happening at idle.

It doesn't help us ID the cylinder that's misfiring, but it does give us a couple hints. One, you don't have an injector stuck open or stuck shut. Otherwise, you'd have found a weak cylinder. Doesn't mean you don't have a restricted injector or contaminated fuel, but we can chase that later.

Two, it would also suggest the ignition coil and injector circuits are working correctly. A broken wire somewhere would have caused a weak cylinder. Again, it doesn't mean there isn't high resistance or a short somewhere.

Going forward, a scan tool is going to be really beneficial. Nothing fancy is needed. BlueDriver would be a solid choice. But even something like an ELM 327 adapter and OBD Auto Doctor/OBD Fusion/Torque would work. The scan tool will give you access to the fuel trim values (which will help you ID which bank has the misfire), but also access to Mode $06 data (which will show you misfire counts).

I've used this adapter with Torque and OBD Auto Doctor in the past:

www.amazon.com/Scanner-Vehicle-Adapter-W...ostic/dp/B076FRK5BT/

  So with the help of a buddy we ran some tests with a really nice scanner. Was watching some of the maps (as shown in pics attached) and noticed that bank 2s readings were way different from bank one so figured we’d narrowed it down to a problem in bank 2. Ended up plugging a seperate scanner into it and the oddest thing happened. Was messing around with some menus and found out I could mess with fuel injection. As soon as I selected it the misfire stopped (mind you I had not messed with the fuel inject but had just started the test) went for a few drives and it drive smooth as ever. So I think we’ve ruled out everything exept for the tune. I ran this revision of my tune for about a month before the misfire started but I’ve heard of a tune “going bad” or the rom file “getting scrambled” let me know what you think. Will be talking to my tuner tomarrow to see what they think aswell as getting another revision. Also we pulled the plugs and non were wet and all looked to be perfectly fine. Attached are screenshots of some data captured. Some at idle and some under load. The ones under load have engine speed as one of the graphs. Thank again!

It looks to me like the bank two air/fuel sensor is struggling. Bank one is spending most of its time around 1.5V like it should. Values less than 1.5V are rich, which causes the Alpha values to take fuel away.

The fact that the engine ran better during the functional test would suggest that it's actually a false rich condition. In other words, the ECM is taking fuel away from bank two when it shouldn't, causing a misfire.

I don't squat about Nissan tuning, but it's my suspicion that you're seeing a feedback problem and not a tune problem. Either the bank two upstream is lying, or the bank two downstream is stuck rich.

So I never mentioned but I have long tube headers on the car and I was told I only needed primary O2 sensors so I have no secondaries. Aswell as I didn’t know I need extended O2s so each side has two regular O2s spliced together. You are talking about the O2 sensors correct? Also uploaded a new tune last night and it didn’t help but running the actuation test still makes the car run fine. Thank you.

Well, We performed a few more tests and came to the same conclusion so we purchased a new Bank 1 upstream A/F sensor and that solved the problem (we replaced Bank 2 first but that did not change anything so we moved it over to Bank 1 and that did the trick).  My only guess relating to the behaviour of intiating the "Fuel Injection Actuator" test is that once you enter that mode the system must ignore the A/F sensor so you can make manual adjustments.  Anyway, I have seen a ton of web inquiries about a random mis-fires so this is one of those examples of an upstream sensor that is working enough to give you bad data.  I was not able to test the wiring becuase this sensor had the wires extended to reach the long tube headers but we could see a ton of black soot on it so it was obvious something was going on with that side.

Thanks again for the feedback and help.  I have looked through a multitude of videos relating to testing wide band sensors and I was unable to make an sense other than to induce an artificial rich/lean condition to see what the computer did with it so does can anyone link a good video on the best way to conclusively test a wideband A/F sensor?

At least the car is back to normal and I am sure he is thrilled considering he has been battling this for the last 3 months (I know the feeling; my Q60 RS was down with a problem nobody could fix for months as well and it sucks).  He was getting all types of feedback to change plugs, coil packs, injectors, etc...  I'm glad he has his car back.

Well, We performed a few more tests and came to the same conclusion so we purchased a new Bank 1 upstream A/F sensor and that solved the problem.  My only guess with the Fuel Injections Actuator test is that once you enter that mode the system must ignore the A/F sensor so you can make manual adjustments.  Anyway, I have seen a ton of web inquiries about a random mis-fires so this is one of those examples of an upstream sensor that is working enough to give you bad data.  I was not able to test the wiring becuase this sensor had the wires extended to reach the long tube headers but we could see a ton of black soot on it so it was obvious something was going on with that side.

Thanks again for the feedback and help.  I have looked through a multitude of videos relating to testing wide band sensors and I was unable to make an sense other than to induce an artificial rich/lean condition to see what the computer did with it so does can anyone link a good video on the best way to conclusively test a wideband A/F sensor?

At least the car is back to normal and I am sure he is thrilled considering he has been battling this for the last 3 months (I know the feeling; my Q60 RS was down with a problem nobody could fix for months as well and it sucks).  He was getting all types of feedback to change plugs, coil packs, injectors, etc...  I'm glad he has his car back.

Well, We performed a few more tests and came to the same conclusion so we purchased a new Bank 1 upstream A/F sensor and that solved the problem.  My only guess with the Fuel Injections Actuator test is that once you enter that mode the system must ignore the A/F sensor so you can make manual adjustments.  Anyway, I have seen a ton of web inquiries about a random mis-fires so this is one of those examples of an upstream sensor that is working enough to give you bad data.  I was not able to test the wiring becuase this sensor had the wires extended to reach the long tube headers but we could see a ton of black soot on it so it was obvious something was going on with that side.

Thanks again for the feedback and help.  I have looked through a multitude of videos relating to testing wide band sensors and I was unable to make an sense other than to induce an artificial rich/lean condition to see what the computer did with it so does can anyone link a good video on the best way to conclusively test a wideband A/F sensor?

At least the car is back to normal and I am sure he is thrilled considering he has been battling this for the last 3 months (I know the feeling; my Q60 RS was down with a problem nobody could fix for months as well and it sucks).  He was getting all types of feedback to change plugs, coil packs, injectors, etc...  I'm glad he has his car back.