Engine Maintenance and Repair of Lexus LS 600h

And hello again!

Late on a weekend evening I'm driving from my parents' place (Smolensk region) to Moscow. Near Podolsk, the body starts vibrating severely. Thinking it's over, my front driveshafts must have failed because I forgot to replace the boots since purchasing them. I stop and turn off the engine. Checking the front wheels manually, everything seems fine; no play or movement. Very interesting... Checked again for any possible movement but found nothing wrong. Back in the car and starting the engine, the violent shaking starts. The check light and orange triangle come on. Here we go. Fortunately, I had an ELM327 to diagnose the issue immediately. Errors seen were: P0300, P0303, P0304. Misfires in cylinders 3 and 4. Fun.
At this moment, I felt like a BMW owner from long ago. Bolts on wheels are 5x120 instead of the usual 5x114.3, check light is on - a full set of issues. Managed to drive home myself with about 20km left.

The next morning, I went through the same process to get to work and start diagnosing the problem.
Rediagnosed it — all the same:

In the evening, I started looking for the cause. Removed all the decorative plastic from the engine, unscrewed the ignition coils, checked for spark - there was one in all cylinders, though the coil for cylinder 4 went into oil.

Cleaned the spark plug hole, put the coil back. Started the engine again — nothing changed except that the error on cylinder 4 disappeared. Began measuring compression. Cylinder 3 showed zero pressure. Well, here we go again. Time to remove the sump and look for rings (knock wood).

Used an endoscope to look inside the cylinders.

Carbon deposits are present in all cylinders with no signs of wear. Very interesting. Proceeding further, I noticed that valve number 6 is halfway up in cylinder 3.

Ah yes, very interesting indeed. Looking at the piston revealed no signs of contact. Thank God... Began googling and contacting acquaintances. Learned there was a recall on early LS600hl models for replacing valve springs because they were breaking. Called the dealership to find out if a recall had been done on my car. They said yes, two recalls in fact: one for spring replacement, another for polishing the fuel rail (I couldn't find any info on this - if anyone knows please share). A friend who used to work at a dealership told me that even if it's noted that service was performed under recall, there's no guarantee the work was actually done.

There’s nothing else to do but disassemble the motor — despite how scary that is.
Reached out to an auto-dock and began purchasing all the necessary parts: gaskets, valve spring kits, VVT-i filter. Just got a call from them saying I would need to wait more than a month for delivery from the Emirates since there are currently serious supply issues with spare parts. And my car is needed right now… Decided to also buy a spring that was available in Russia and replace it first, then later on change all others.

During repairs, my friend sas-darm lent me his car while he was on vacation - huge thanks! I moved around with BMW but without the check light on.

Started disassembly. Removed all ignition coils, disconnected the battery and VVB fuse. Unscrewed the expansion tank of the inverter.

Unscrewed some electronic block that got in the way (didn't want to know what it was at that time).

Correspondingly detached all plugs that blocked disassembly.

Decided first to check the right cylinder head for broken springs - not much more work and I'd feel safer.
Disconnected the wires of the inverter:

To prevent dust from getting inside, taped up all openings on the inverter with painter's tape. Cleaned out the engine as well as possible and disconnected fuel lines from the right injector pump, removing it.
Removed the right valve cover.

Checked all springs - everything was fine. Dismantled the valve cover to examine the VVT-i valve filter. As it turned out, not in vain.

Cleaned it to the maximum degree of cleanliness and installed back since new filters will be arriving very soon…
Reassembled everything again. Moved on to the left side.
For safety took photos of tubes arrangement on the left injector pump.

Analogously with the right one, removed the left valve cover.

Immediately found the culprit:

Checked other springs - all good. Disassembled valve support — piston + air.

Broken spring of a valve:

Original part number 90501- 35046. Part number for the problematic spring was 90501-33022.

I reassemble the valve back on.

Next, I check the VVT-i valve filter under the left valve cover in the same manner as I did with the right one.

It's hidden behind this insert:

The condition is similar to that of the right filter. I clean it and put everything back together.

I didn't see any point in taking photos here since I was reassembling things in reverse order.

And there's the first start-up after assembly, at five in the morning.

Turns out I hadn't tightened the fuel lines for the left side of the pump properly. Tightened them up and everything is fine now.
In my excitement, I decided to clean the engine from years of grime:

With decorative covers as well:

Now the engine runs as it should. Still considering replacing all springs and rubber parts on a holiday or something similar. The hardest part will be changing the springs for cylinders 7 and 8 since they're very hard to reach without wanting to remove the entire engine.