E90 320i (N46) Misfire

[DarrylvanNiekerk]

Good evening,

I have been battling with a persistent misfire which I just cannot nail down.

If I start the car and spray a jet of water onto the exhaust as the branches are heating I can see the misfire is on cylinder 3.

I have swapped coil packs, checked spark plug gaps, swapped injectors and the misfire stays on cylinder 3. I have cleared faults and there are no codes present.

I can't see any damage to the coil plug or wires and the brown plug wire is grounded.

The only thing seemingly left is that signal isn't being sent by the DME or is there something else I am possibly missing?

When I pulled the plug it was wet with fuel. There are no compression issues.

I have been trying to figure out the issue for the last few days and now the half orange check engine light has come on.

Any advice would be greatly appreciated.

 

[DarrylvanNiekerk]

Update on the issue above.

I pulled the DME out and checked continuity of signal wires to coils which there is, continuity also exists on the ground wires. Power wires send 12v to each coil plug. All spark gaps are 1.1mm.

I pulled out the plug and coil pack for cylinder 3, grounded it and turned the car over, there is spark.

I pulled the fuel rail with injectors out and all 4 injectors spray nicely in the correct order.

I did a compression test and all cylinders have around 13bar pressure after 7 cranks.

I have taken the tappet cover off and there are no obvious signs of hydraulic lifter issues. Timing is still correct.

Is there anything else I can check or do I just send the DME for testing?

 

[evnmopwr]

Did you scan the car for codes?
That would be the first thing to check

Maybe its a past code that's causing this.

a Scanner with live data option could also maybe help

 

[DarrylvanNiekerk]

After a huge amount of back and forth trying to figure out what the issue was it seems I may have resolved it with a number of fixes.

I found a bit of damage to the wiring of the plug for injector number 4. Luckily I was able to source a second hand plug and wired that in place. This did make a bit of a difference but nothing major.

After a little more research I discovered the downstream O2 sensors had their wires cut. I bought two second hand sensors and fitted them. This made quite a big difference but the car was still running rough.

I borrowed a launch, cleared codes and then looked at the live data for the Lambdas. I noticed the readings were way out so I swapped the plugs for the upstream O2 sensors.

Suddenly the car was running a lot better, almost completely clean. After idling for a bit and then a short drive and things are looking pretty normal.

The last step will be to get the software back to stock and drive it a bit to see how things go.