Car is a 2006 4.2 V8 Supercharged with 130k miles, no LPG.

Developed a misfire on bank 1, GAP iid tool plugged in and codes below:
P0300 - random multiple misfire
P030X - misfire detected on cyl X, (X being 1, 3, 5 & 7 (all bank 1))
Bank 1 is offside, drivers side in RHD UK car.

Worst culprit when logging the misfire counters is cyl 5, for example this will count 200 misfires in the time cyls 1,3,7 have counted around 30 for example.

Things tried so far:
Changed coil packs
Changed spark plugs
Smoke tested - no leaks
Cleaned MAF sensor
Cleaned throttle body
Compression tested - all cyls ok
Monitored injector pulses with Picoscope - pulses fine and all the same
Checked grounding - all ok
Wiring to injectors ok
Fuel rail pressure ok
Full tank of super unleaded
Lambda sensors swapped
Camera in plug holes, cant see any issues with valves.

Observations/comments that may or may not be relevant:
Plugs are slightly wet/black on bank 1
Outside air temp sensor reading nonsense, cant find it in the front bumper where it should be still need to locate this.
Worth swapping cam sensors over on banks?
Possibly timing off on bank 1?
Gets worse under load when revved slightly, but can feel the car slightly shakes even on idle.
Not driving car at all since this issue began. No idea why it started, cant link it to any events etc. car didn't overheat or anything like that.

Looking for advice what to try next. All and any ideas gratefully received. Thanks

Last edited by Parallel on 13th Apr 2024 9:34am. Edited 1 time in total

It's your sc coupling going or the bearings and the nock sensor is picking it up and registering misfires when it's not. Here is my issue same engine

https://www.rrsport.co.uk/forum/topic59795.html

Thanks for the idea Dave, unfortunately don't think this is my issue. SC bearings all fine and checked for play when I removed it to do injectors. It's not just a detection issue, it's definitely misfiring. A bearing would get progressively worse over time, whereas this has been more of a step change. Appreciate the info and glad you got to the bottom of your fault.

Fingers crossed you get it sorted these are a for misfires, have you looked at the pcv yet ?? You can block.it off and see if anything changes I see you smoke tested it I did the same and found a small leak behind the throttle body where a plastic pipe pushes into the head the O ring there had failed also causing misfires. Common problem.
Good luck

Cam shaft sensor jumps out at me as being cause

I'd agree with the cam sensors as a possible place to check too. If the sensor is giving duff infomation to the ignition system, then it could lead to mis-fires.

Beyond that ... you've mentioned the plugs being wet / black. Black suggestive of carbon deposits from a rich mixture, and wet suggestive of fuel unburnt ... so if its throwing in too much fuel, it'll burn what it can, some will carbon deposit because of a poor burn, and the unburnt fuel will be wet. So it sounds like its running rich.

The system will inject fuel based on what the sensors are telling it. I'd need to look into the workshop manual as I never really had any issues with my old one to figure out what sensors there are.

I'd be sniffing around the sensors to ask myself:

- Is the MAF giving plausible readings? ( just cause its clean doesn't mean its sending out the right values ... maybe worth asking others to post their idle readings and 2000rpm readings when at standstill as a comparison )

- Are there left and right sensors for any parts of the system? and are they showing matching readings? ( cause they should I would have thought ) ( pressure, fuel line pressure, injector timings, O2 sensors on the down pipes ) Anything that may show any noticable reading difference between bank 1 and 2. V8 or else ...

Thanks for the replies chaps. I have looked at the PCV and had it off with engine running, didn't cure the misfire and appears to be working correctly.

With regards to sensors Fisha, I'm with you that cleaning MAF doesn't mean it's working correctly, however it's only 1 MAF sensor for both banks so don't see how it's fine on one bank but not the other? I agree that it seems like a sensor issue, as it's putting in fuel for a reason, which surely must be that the ECU is calculating it needs it due to an input which I assume is MAF readings only?

I also think it's running a bit rich on bank 1 due to the condition of the plugs, and the exhaust on that side smells like somethings not right too. Looking at lambda sensors they are working a bit harder bank 1, and this stayed true when I swapped the lambda sensors over also.

Fuel pressure is common for both banks as it's all one rail.

Good idea looking at MAF readings, I'll try that when I get time. May try and swap cam sensors over too just to rule them out, but think the SC has got to come off again for the third time to get to those.