I drove the car back home from the dealer (about a 45-minute drive) and then checked for excessive pressure in the coolant tank. To my surprise, I was able to open it easily - there was almost no pressure at all. On my previous BMWs, it always took some effort because the hot coolant created pressure.

Next, I used the head gasket tester. Let the car idle for a good 10 minutes while pumping the tester, and the liquid stayed blue the entire time.

At this point, I’m not sure what to check next. I’m thinking about removing the bank 2 catalytic converter to see if it makes any difference, and also inspect the inside of the cat.

 

You got a vaccum leak if it only misfires on coldstarts monitor the long and short term fuel trims

 

Another update:
I unscrewed the exhaust bolts and moved it on side so the exhaust gases went straight into the air. All sensors stayed plugged in. No improvement at all - in fact, it felt even worse. The misfire counter showed 200+ misfires for cylinders 5 and 6. Normally, it’s in the 17–60 range, so maybe just a coincidence, who knows. I put everything back together. Added some pictures of the catalytic converter - not the best quality; I definitely need a better camera.

I also swapped injectors from Bank 1 to Bank 2. When I started the car, no misfires were registered, but the RPMs were fluctuating. Turned out I had forgotten to plug in the throttle connector. Once I plugged it back in, RPMs stabilized and still almost no misfires.

I left the car overnight and released the pressure from the coolant tank just in case. Next morning, I started it and got 50+ misfires on cylinders 5 and 6. No CEL this time.



I took the car to an independent mechanic. He sent me a video showing that cylinder 5’s compression builds up slower than cylinder, 6- sec vs 4 sec to build up 125 psi. He suggests it might be piston rings. But how could it be the rings if the leak-down test showed only about 5% leakage? Now he’s suggesting a BG service.

 

check the exhaust buckets see if they haven’t punched through, stupid common on these engines. if you have an in-cylinder pressure transducer you can find it that way too and it’ll save you a ton of teardown time

it’ll pass a leakdown test because the cam isn’t acting on the valvetrain. running compression on a scope never lies

 

That’s a great point. I don’t have an in-cylinder pressure transducer right now, but investing in one seems like a smarter move than tearing the engine apart. Do you have a specific model or brand you’d recommend, and what’s the usual price range ? Also, I’ll need an oscilloscope that works with a laptop, any suggestions on that as well?
.

 

i have a wps500 and a 4 channel pico but it's not DIY budget friendly. a pico 2204 will be enough for this and it used to cost peanuts, check on the used market you might find some good deals

rotkee transducers are apparently good you just need to set it up with the right hoses and adapters that they sell, 5.0 uses m12 spark plugs so get the flexible hose and the m12 adapter

 

Thanks everyone for your replies.

Here are the pictures of the cylinder walls. I’m pretty sure these scratches shouldn’t be there. Is this considered normal wear, or does it mean the engine is done?

Cylinder 1, which never misfires, looks about the same as cylinder 5. I checked other cylinders and they looks similar too.
Cyl 1




Cyl 5

 

Typical lubrication fail. The horisontal honing is lost and that will increase temp of piston and piston ring. (by increased friction)
Lubrication fail can be caused by wrong type of oil, too long oil change intervals, too low oil, coolant wash, fuel wash by leaking injector or issues on ignition system.
All is not lost, but pushing engine hard can cause piston or ring seize. This is still fixable by honing work if the cylinder bore roundness are still in tolerances.
I would recommend to check the coating of piston shirt and replace the rings while in there.
If cylinder roundness exeeds its boring work with oversize pistons.

 

I don't think that is your problem, looks normal wear to me.
Leak down test would have shown up a significant problem.
Piston is very clean, how come ?

 

The car has 67k miles. There’s some deposit on the pistons, but it’s probably not visible in the photo because of the lighting. All pistons look about the same condition.

I soaked the cylinders with Orval oil and Berryman B-12 Chemtool(1/4), just in case it’s a stuck ring. I’ll check tomorrow to see if there’s any improvement.

 

Absolute not normal wear. At least not at 67t miles. Seen engines over 300t miles (500t km) still having cross hatch honing grooves well present all around cylinder walls.
When honing grooves is lost there are no pockets for oil to stay and keep parts separated.

 

Absolute not normal wear. At least not at 67t miles. Seen engines over 300t miles (500t km) still having cross hatch honing grooves well present all around cylinder walls.
When honing grooves is lost there are no pockets for oil to stay and keep parts separated.

 

You are entitled to your opinion. They all look very shallow marks to me. You really think there is enough 'damage' to cause misfiring even though the leak down test was good ?

 

No, the losing the Cross-hatch finish honing do not cause misfiring, also no effect to the leak test at all. Its not for sealing, its for lubrication. In high propablity its one cause generated by the issue itself. Good on this are that this could lead you for the actual fault.
My penny:
* Since you are not loosing coolant and there are no exhaust remains on coolant - Coolant wash can be ruled out.
* I do think that you have been changed the oils and used good quality oils, so in high propality we can rule engine oil out as well.

I put my bet on fuel wash:
- Maybe your ignition don´t ignite the mixture every time : Spark plugs / coils. OEM? (counterfeights in market)
- Maybe your injectors leak or make droplets? (forget the correct english term) Again: LOT of counterfeights
- Sticking or leaking valves, lifters or rings? Low combustion pressure make poor burning and unburned fuel wash the cylinder liner everytime piston goes back up after "bang" cycle. (hardest to find, but if moving coils, sparks, injectors around and issue stays on same cylinders, then this is something what is left...)

I have done "few" engines myself (for racing) and blown up as many for my own mistages or just .. Well, we call it Motorsport when everything goes bust and you swore it was last time you do this sh*t, but then next weekend you have tools on your hands again...
After moving coils, sparks and injectors around and if the issue still staying on same cylinder(s) i would suspect something on these cylinders itself.

 

The thread is long, so here’s a quick summary of what I’ve done so far:

• Replaced all spark plugs and swapped them around
• Replaced all Bank 2 injectors, then swapped Bank 1 injectors to Bank 2
• Swapped coils multiple times
• Performed a leak-down test and block test
• Flushed the engine with BG 44
• Did a piston soak using Mystery Oil + B12

Regarding coolant loss: I’ve driven about 200 miles since topping it up, and the level might have dropped about 1 cm, but it’s still at max. If there’s a loss, it’s extremely slow—possibly just minor leaks from plastic connectors.

The only thing that really stands out right now is the compression:

• Cylinder 1: 127 psi, took ~4 sec to build up
• Cylinder 5: 115 psi, took ~8 sec to build up

After about 50 psi, it builds up much slower.


With all that said, here are the misfire patterns:

• Cold start: Cylinder 5 misfire is always present.
• 3 out of 4 times, Cylinder 6 also misfires.
• Cylinders 7 and 8 misfire occasionally.

When the car warms up (1–2 minutes), the computer barely detects any misfires, but I can still feel a slight vibration. After driving ~20 miles, I get a catalytic efficiency code. Bank 2 O₂ Sensor 2 readings fluctuate between 0.2–0.7 V, even after adding a small spacer.

 

Are you aware of this cylinder numbering?

 

That is a very interesting point. The 2015 Range Rover actually uses the DIN cylinder numbering system and is different to the earlier AJ133 engines which follow ISO numbering. (I think the change happened in 2014).

DIN Numbering

Bank 1 (right hand) is 1,2,3,4.
Bank 2 (left hand) is 5,6,7,8.

So if one is troubleshooting while following the ISO numbering system as quoted by Kansanbrit, the results will be very confusing.

 

The numbering is clear, confirmed by unplugging coils while checking live data.

 

Hi everyone,

Sorry it’s been a while!

I still haven’t given up on the car - it’s become a personal battle at this point 😄

The misfire is still there. I’ve pulled the engine out and plan to do a full rebuild, assuming the block and heads are still in good shape. It’s going to be a long road ahead with disassembly, and I’ll probably start a new thread later once I dive deeper.

Current observations:

• It’s pretty clear someone’s been in this engine before - a few brackets are missing.
• There’s one broken bolt on the bank 2 valve cover (not a big deal).
• More concerning: one of the bolts that secures the supercharger to the head came out with the partially thread still on it. That’s the bolt between cylinders 5 and 6 - the same area where I’m getting the cold-start misfire. Not sure if it’s related yet, but I’ll find out as I tear it down further.
• Some areas look slightly rusty, not sure if that’s normal.
• Also noticing some wear marks on the camshaft lobes - could someone please let me know if that’s typical or something to worry about?
• Lastly, I’m not sure if I need to replace the timing chain. Mine looks to be in pretty good shape, but I’m not sure how to properly check it. I just don’t want to replace it unnecessarily if it was already done by the previous owner.

Rust on camshaft

Please observe the spots on the tip of the lobe

 

I think this cam lobe is totally gone. Looks like someone grinded it down with sand paper
for whatever reason.