Cold start missed fire on EZ36

[oakleyyu]

Hi everyone! Just wonder how would I be able to deal with a cold stater missed fire on EZ36 travelled around 100k?
Have changed to new plugs already no clear signed of leak from head or failure in gasket, a little missing fire in one cylinder (closest to passenger side, cylinder6 I think) when cold start but return normal after running hot. Check the compression ratio and unsurprisingly its lower than standard (8.25bar for the missed fire cylinder and 9bars around others, 10.5bar is the standard sepc) Is this a typical subaru thing or I should do something now, cheers!

FYI, I've got a 2015 Subaru Liberty 3.6R, the car has been serviced regularly with quality fuel and suitable grade, I've also suspect it might be a ignition coil problem so I swap two coil when changing the plug but the problem stayed with the cylinder. The over all condition of the ignition coil does not look bad though.

The problem is not even noticed a problem as I thought the rattling and noise is normal for this car when cold start, and never had I got a light in dash, until I bring it to mechanic, plug in a obd, it can have numbers showing missed fire in cylinder 6.

[bigBADbenny]

How did you go with the issue, any progress?

You can try a real life automotive diagnostic technician, ask for a misfire diagnostic *quote* after discussing the symptoms.

That’s to prevent a mechanics parts cannon solution which can be expensive and ultimately frustrating if the issue isn’t found through a non diagnostic approach.

That’s once you’ve done the basic afr, fuel, spark, cam & avcs timing & injection related misfire DTC or evidence/interview troubleshooting & diagnostics you can find in your FSM workshop manual available free or paid online.

A competent auto technician might run through those ^ basics, before using an oscilloscope and a variety of sensors and tests to get to the exact issue with less assumption.

A ‘scope enables an extremely thorough yet fairly non intrusive view of eg relative compression and in-cylinder pressures during a single engine cycle, the latter generally during forced crank no start.

This is essentially similar to doing a cylinder compression and leakdown test, but with the added advantage that the specific mode of the fault causing the misfire code and other symptoms can be isolated to individual valves in the affected cylinder, should the evidence lead to that prognosis.