Misfire above 2000 RPM

[MartinS]

Hi, new problem with my engine: fixed Trigger 2 ground issue noted in previous post.  This morning started and ran perfectly.  Took it out for a drive and all good until around 2000 RPM when it begins to misfire.  

I have looked at the log and there are no Trigger errors (thank goodness!). The only thing I can see is the mixture goes lean during the misfire which is expected.  I tested the ignition and injection channels using the capability in the ECU and all test ok.

My problem is: I have just rebuilt the engine with new bearings and rings.  It has less than 5km on it.  Everything I'm reading about breaking in an engine says do not let it idle for long or run it at increased RPM without a load.  I'm very reluctant to test the spark and injectors running the engine above 2000 RPM in the garage.

Is there a way I've not found to see what is happening in the log? I have attached a link below to the log of the drive today. Does anyone have any ideas how I can investigate this without running the engine up in the garage with no load to find the issue?  Or am I being to cautious and should just go ahead and run it?

Thanks in advance.

https://drive.google.com/file/d/1jXmhRmyqrauGkaNZ5Yu1JZhLRzuiN0vT/view?usp=share_link

[MartinS]

Ok, on further examination I found a crack in one of my ignition plugs (at the coil).  Replaced this and went for a drive.  Better but still some hesitation/missing.  Fairly subtle though which I found confusing. 

Had turned my knock sensors back on (I keep forgetting the routine to keep them on) hoping I could tell something by looking at the individual cylinder channels to see which cylinder was missing.  Didn't seem to help as they all look the same. 

Then I noticed my RH Intake cam sensor is not working so that cam isn't being advanced.  Now I'm wondering if the power imbalance between LH and RH cylinder banks is the source of the unevenness here.  The cam advance makes a huge difference to engine torque at the RPMs I am noticing the problem so there would be a significant imbalance.  

Fingers crossed, I'll fix the sensor output and see if that fixes it.  I'll report back...

[MartinS]

Hi, fixed RH Cam position sensor and cam advance working well.  Went through wiring to make sure no issues and didn't find any.  Still have misfire(?) starting around 2000 rpm.  

Anyone have info on whether G4 Xtreme can analyze and identify which cylinder is causing problem? Online info says many ECUs can analyze trigger signal and figure out which cylinder is the problem but I'm not seeing if that can be done with Link ECU...

[MartinS]

I forgot to mention I did run with knock control on and this led me to investigate cyl 4 more closely.  Good spark and injector clicking when tested (all are).  All other cylinders equal knock levels. I tried unplugging each coil while running to see if the irregular running didn't get worse with one cylinder.  

With any of the cylinders unplugged, the running became much rougher with none seeming to make more or less difference over the others.  While only on 5 cylinders (didn't matter which), the engine continued to have the rough running/hesitation I'm investigating overlayed on the rough running from 1 cyl off.  The roughness from one cylinder off was very regular, the roughness I'm noticing is much more irregular and of higher frequency.

Only thing unusual is the engine seems to run fine for the first 30-60 seconds after started weather hot or cold (maybe a little longer when cold?).  As noted, all wiring seems correct and in order, no errors or problems noted.

Because of all this, I'm beginning to think this is not single cylinder 'misfire' but something affecting all cylinders.  When running and driving I've looked at all the runtime values and there is nothing unusual (ie no trigger errors).  

Have included 2 logs of the engine running and having this issue (since correcting the RH cam position sensor).  Apologies for the second file, I forgot to stop recording after getting in garage so long period of dead air.

https://drive.google.com/file/d/1_JfHXP9O0hnnoXFyZUFvf9R2QGpMLdze/view?usp=share_link

https://drive.google.com/file/d/1r_zC3WCuxcOnBOpGhBUvKSObNdjOZuVf/view?usp=share_link

[neil brown]

Have you done a compression test on the engine as low compression will give you a misfire 

 

And what engine are you running as well 

[MartinS]

Subaru EZ36, new rebuild.

[MartinS]

Fuel pressure >35psi.  Spark plugs carbon on rim with whitish deposit on electrodes.  No single plug is different colour.  I've tried richening the mixture but then it runs rough with a richer mixture.

When removed from the engine prior to bottom end rebuild, plugs had minimal pinkish deposit of good mixture.  At that time the engine was running pretty much perfectly until my first rebuild spun a rod bearing...just plain old bad luck according to my machine shop.

Same plugs, same coils, same injectors and wiring, same ECU and tune, same top end.  Spent the weekend hardwiring the engine wiring loom to the ECU (was using the Subaru engine plug and socket original to the engine, some of the 32ish small sockets were beginning to cause fail as they don't like being unplugged and plugged in more than a few times it seems...this was the cause of the intake cam position sensor signal failure as well lost oil temp signal).  I was hoping this was the source of the issue.

Obviously I've reached the limit of my diagnostic abilities on this.  Any help would be greatly appreciated.