general misfire at idle - need help in diagnosing

[cfauvel]

Ok so my car (2005 nissan 350z) started misfiring at idle and now whilst running too.

When it happened the Service Engine Soon light started blinking.

Unfortunately the misfire is not throwing any other code other than p0300 which is a just a generic misfire. Would BE super helpful if the computer had a more specific cylinder being reported.

All I have is a couple of cheap scanner and an Autel MD806 Pro

Using the cheap scanner I was able to capture live data and noticed some weird values for Short Fuel Trim on bank 2 when it misfired, so I believe I have at least narrowed down to which side of the motor is the issue. Bank2 seems to be the left side of the motor (looking down onto the motor with front of motor pointing up )

when it was not missing the short term fuel trim were about
shrtft1 -2.3
shrtft2 -3.1

when it started missing the numbers were
shrtft1 -2.3 to -3.1
shrtft2 12.5 - 15 (positive)

So what is my next steps to diagnose? I don't have a picoscope (I did always wanted one. ) to attach to see if the coils are firing or if the injectors are firing. Could be the cam position sensor.

I'll run the Autel MD806Pro today to see if picks up more information....it usually does.

[VStar650CL]

Not sure what you mean about "looking up" at the motor, but bank2 is the driver's side of the engine. I'd start with a power balance test to see which cylinders are weak or misfiring. If the whole bank is affected, the cam sensor is a likely suspect. The ECM's aren't very good at detecting malfunctioning sensors, only flatlined ones. So when they start missing teeth on the reluctor, it often doesn't cause codes, but it screws up the injector timing and the ECM compensates rich.

[cfauvel]

"Not sure what you mean about "looking up" at the motor," Taking a picture of the motor as a bird is flying over head...then rotating the picture so the front of the engine is pointing up.
the distinction about driver's v passenger can be misleading as there are countries where the driver's position is on the right....japan, UK, AUS, come to mind....but being the USA yeah it is the driver's side/left side

"I'd start with a power balance test to see which cylinders are weak or misfiring" great tip, how do I do that? What additional tools would I need to do that?

I put my Autel MD806 on there and didn't give me much more info than P0300 ...and didn't have any freeze frame data.

Put my cheap scanner on there again and it DID have a freeze frame stored for the p0300 and basically showed the same short term fuel trim on bank 2 being out of whack.

Someone on another forum suggested using the scanners to see the misfire counts per cylinder, but have been unable to find that screen on the Autel MD 806

NOTE: as I started the car, it was misfiring right off the bat. after several minutes I got about 10 seconds of it running right before going back to misfiring.

I suspect you're right that it is a cam position sensor (of course the harder one to get to), but without a definitive code to point to a particular cylinder I'd hate to throw parts at it.

[VStar650CL]

The list of stuff that can cause a one-bank-only malfunction affecting more than one cylinder is pretty short. Your engine doesn't have twin power valves, and the way the plenum is arranged makes a vacuum leak affecting one side unlikely. You don't have separate subharnesses for the banks like some other models, only the two right-front coils are on their own sub.

If your scanner doesn't have work support for power balance, you can do a poor man's balance test by simply yanking coil connectors one by one and watching how much the RPM's drop for each cylinder. Weak cylinders will give you less drop than healthy ones.

[cfauvel]

"If your scanner doesn't have work support for power balance, you can do a poor man's balance test by simply yanking coil connectors one by one and watching how much the RPM's drop for each cylinder. Weak cylinders will give you less drop than healthy ones."

Ahh yes the "good ol' pull the plug wire off " and see test....in this case coil wire... thanks yeah I'll do that.

[VStar650CL]

Or injectors, but on most rides that's harder.

[cfauvel]

Or injectors, but on most rides that's harder.

Way harder on the 350z....grrr

[cfauvel]

UPDATE: I think I fixed it..... I guessed it was the left side bank 2 camshaft sensor.

I luckily had a used spare one from my wife's G35 of the same year.

of course the driver's side is a little tougher to get to , and the connection type is a bear. You have to push in on a lock and continue to push in while trying to disconnect the two. I find it easier to remove the sensor with the wire connector still on and then wiggle the whole thing up and out to better see it and use both hands. (if there is an easier way to disconnect the camshaft sensor connectors PLEASE let me know.....THAT was the hardest part )

Started it up and it is no longer misfiring.....I went ahead and bought a new Hitachi sensor and will replace it again so I have a new one on and a working spare for future diagnosis.

[cfauvel]

T you can do a poor man's balance test by simply yanking coil connectors one by one and watching how much the RPM's drop for each cylinder. Weak cylinders will give you less drop than healthy ones.

I tried to get to the coils on the left side but they're buried under the plenum intake tube ....right side wouldn't have been a problem.

Seems to have been the camshaft sensor, I had a spare to test it out.

[VStar650CL]

Your best friend with those connectors is WD40. Flush and lube the plastic shell before you try take them loose, they'll usually require a fraction of the effort. People only think of WD for rusty bolts, but it works great on cruddy release pawls too.