Hi, Getting code p0303 on my 2009 Murano, cylinder 3 misfire. I replaced, coil, spark plug and fuel injector. Still get same code. Checked compression on number 3 and it is at 195. So don't think its a head gasket. I don't see and oil or antifreeze mixed. Any ideas on what to check next? I'm going to try intake manifold gasket but it does look ok.

That 195 is way high, standard is 185. Typical VQ's that old will come in around 170~180. So you may have a bad case of carbon on your piston crowns. That happens frequently on transverse VQ's if they aren't driven hard, especially on the back bank, which is where your problem is. Have you checked for spark with a known-good coil, and checked for power and ground to that coil connector? Have you checked for 12V at the injector and put a noid light on it to see if it's getting signal from the ECM?

I did check spark by just taking the plug and coil out and watched the arc on the plug while cranking the engine. So i was getting voltage. Never used a NOID light. Can I use a voltage tester?

Not as easily, but yes. When you turn the ignition on with the engine off and back-probe the injector connection, you should see 12V on both sides of the connector (possibly very slightly lower on the ECM side). That's because the ECM driver will be open-circuit and the injector coil is acting as a "pullup resistor" to the other side. If there's no voltage on either side then there's a problem with the 12V supply wire. If you only see 12V on one side and the other side is near zero then the injector is bad (open circuit in the coil). Then back-probe the ECM side of the connector with the engine cranking, you should see a lower voltage on the ECM side than the 12V side. If not, there's a problem with the trigger wire or the ECM itself. The best way to ascertain the voltages you should see are to measure a good cylinder and then compare to the misfiring one.

Thanks, I'll check

Check the airbox intake hose. Mine was dry rotted and caused my ‘09 to run terrible.

Murano2009 wrote: ↑

Tue Feb 27, 2024 3:12 pm

Check the airbox intake hose. Mine was dry rotted and caused my ‘09 to run terrible.

Yes and the lip on the Throttle Body is very narrow, so the rubber boots on older Muranos are infamous for falling off. However, you won't generally get a cylinder-specific misfire from that, P0300 and P0101 plus lean codes are usually what happens from a bad or dislocated boot.

Yeah, I already replaced the boot over the summer since it feel apart causing other errors.

Today final got to replaced all the plugs and intake gasket. I was only able to check that I had 12 volts going to one side of the fuel injector. I wasn't able to get into the back of the injector it was sealed so I just unplugged the connector and checked that one pin had the 12 volts with car on. I did spay starter fluid around but didn't get any change in idle. I also replaced number 3 coil for a second time, you never know.
Symptoms: Error code is misfire Cylinder 3. (Just to be clear I'm working on the firewall side middle plug)
The code doesn't set while idling, but is a little rough. It sets when I get up to 15 to 20 MPH.
Done so far:
1) Coil for number 3 & 1
2) All spark plugs
3) All fuel injectors
4) Intake manifold gasket
5) Have 12 volts on one side of fuel injector. (Wasn't able to check other side with volt meter)
6) Compression on number 3 is around 195.

What do you think? I guess the ECU is next.....

Can I drive the car like this or will it damage something.

Depends how serious the misfire is. Raw hydrocarbon overheats the catalyst as well as potentially washing down the cylinder wall and polluting the crankcase. None of those are good.

So you agree to replace ECM module? Are there any special steps I need to do with this replacement? I will most likely get one from a salvage yard or ebay used.

I think I'd spend a couple bucks on a 'noid light before condemning the ECM, and do continuity, insulation, and pin-fit checks on the injector wire.

The ECM won't be plug-and-play. At a minimum, it will need to have the keys reprogrammed and an IAVL/CTPL executed after installation. The VIN is also stored in it, so it should be reprogrammed for that (although you can get away without it if everything else is okay). The real problem is that the only part number on the ECM will be the Hitachi number, which doesn't tell you what software is inside. So unless you get the VIN from the donor vehicle and confirm that the donor had identical equipment to yours, there's a very good chance the software will be mismatched. On older vehicles there's often no utility in Consult3+ for a "new blank" program, so it's possible the dealer won't be able to remedy the mismatch and you'll need to send it out to a reprogramming service.

Ok, I'll pick up one of the kits to check, it will take me a few days to get the kit.. Does the car need to be running for an accurate test? Since I have to remove the intake, connect the light, put it back together and route the cable somewhere I can see the light? Or can I just crank the engine a bunch of times.

Cranking is fine, running isn't necessary.

Finally was able to back to the car. I did the test with the NIOD. It does flash, so the ECM is working. I'm at a loss of what to do next.
The car does run rough when driving so there is a misfire. I even ohmed out the wires back to the ECM and they are good.

The code on the car is P0303 $07E8 - Cylinder 3 misfire detected.

I re-did the compression test just to be sure and it was 180.

Please any other ideas?

The noid light won't lie, so you can pretty much rule out an ECM problem. The 180 compression is a lot more normal, your 195 must have been an artifact. So back to basics: What sort of components did you use when changing out the coil and injectors? What does the burn look like on #3 plug and piston crown compared with the other two on the back bank? Does the exhaust have any smell? Very rich will give you a black or even wet plug and might indicate a rolled o-ring on the injector, usually accompanied by an acrid odor in the exhaust from the cat being overworked. Very lean will give you a whitish plug burn and may indicate the new injector is sticky or the wrong volume.

PS - You can discriminate rich from lean pretty easily using a spray can of something combustible. Spray down the barrel past the air filter and see if the rough idle stabilizes momentarily. If it does, then you know #3 is fuel-starved.

I did check the spark again and the plug is dark but not wet I didn't compare against the other two. I will spray down the barrel, no smell or black smoke for sure. I would have thought the problem would have changed a little with new parts even if not top quality. Never know..

I never recommend aftermarket or reman injectors to anybody, and when I bought eBay spark coils for my '04 Altima daily, I bought 6 instead of 4 because I figured at least one would be bad out of the box. Turned out to be two. 'Nuff said.

Well I'm really at a loss, now.

Swapped injectors and coils to different cylinders.
I even replaced the connectors on injector 3 and coil 3.
I thought it was good when I started the car it sounded normal but once I drove the car the service engine light flashes and I get a pending code P0303 (Cylinder 3 Missfire) around 20 MPH. You can feel the miss-fire. I thought maybe the fuel rail had something stuck in it but the gas just pours out when you remove the injector.

What do you think?

Then I think we're down to a wiring or connector problem with the #3 coil or an actual problem with the cylinder, like a truncated cam lobe or a blockage at #3 in one of the manifolds. Normally checking the wiring is just a matter of back probing the suspect connector and looking for voltage differences with a good cylinder, but that's not practical on the back bank of a transverse VQ. So get an adjustable spark tester like this one and see if #3 is throwing as good a spark as the others in the bank. If it isn't then you know you have a connectivity issue, if it is then you know you're looking elsewhere.
https://www.autozone.com/test-scan-and- ... pps.s=2398

Hi Vstar, first off I wanted to thank you for all the information and troubleshooting steps. The issue is resolve. The new coil purchased from the local auto store was bad. I was passing on your steps to my son who didn't move the new coil after replacing it during the first step. I was able to physically work on the car today and did the spark test. I used cylinder 2 as the basis. Once I had the base line I decided to move plug and coil to 3 from two and had great spark. Put it back together and the problem moved to 2. Inspecting the coil we found the bottom had staffing on just above the rubber boot. So it was shorting out. Again thanks.