IS200 turbo - AFR issue, misfires/knocking, advice needed !

[Alex787B]

Hi mates, this message will be a long one as I'll try to be accurate and provide all the details related to my issues.
Thanks in advance for reading, and here's a small summary to begin :

Summary : I have the car for 1 year approx. Stock IS200, coming from the UK. 120 000 miles on the clock.
Encountered some issues with my ignition system last summer. Replaced coils 2 times and the issue disappeared.
The car was running OK for weeks, and I decided to get it turbocharged using the eBay turbo kit. Low boost pressure (0.2/0.3 bar), first cat has been replaced by a custom downpipe, other parts of the exhaust are stock (2nd cat still in place). The car is running on stock mapping.
Now I have AFR problems - as RPMs go higher, AFR goes from 12/13 to 15.9. Above 4500 RPMs, I'm starting getting knocking. Check Engine light comes even on idle, and OBDII reader says "Misfires detected on cylinder 1, 2, 3", "Random misfires detected", "System too lean". As the car is totally stock except the turbo, I'm looking for the weak point(s) causing this.
More details below !

So I'll start with troubles I had with my ignition last year, as it may be related to the issues I have now.
Last summer I started experimenting power loss above 4000 RPMs. No vibrations, no Check Engine Light, only power loss.
I replaced the coil packs with 6 new coils coming from eBay. I got it running OK for about 1 week, then the issue appeared again.
I thought it was related to cheap coils, so I bought new Magneti Marelli coils and fitted them. I got the car running fine for 1 month approx. Then I got a dead cylinder's symptoms - vibrations, check engine light saying "misfire on cylinder 5", constant power loss. So I took away that coil on cylinder 5, and put back one of the eBay ones - the car was running fine again and the problems never reappeared since.
Strange.

Then I got my turbo kit installed in the beginning of this week. The kit includes the following : turbo, manifold, intercooler + piping, air filter, oil returns and hand welded downpipe. I still have the stock exhaust, with 2nd cat still on. First cat has been removed to be replaced by the downpipe. So, my boost pressure is somewhere between 0.2 and 0.3 bar. All of that runs on stock map, there is no standalone nor piggyback, only a small black box with no reference on it hooked to the ECU (4 wires, +, ground, green and yellow).
I also added an AFR gauge to the install... and it was worth it.

Got the car back, and then I started to test it step by step on my way back to London where I was spending the night, before I get home to Luxembourg.
Cruising, the AFR is between 14 and 15. Nothing to worry about I presume. When the boost comes up, at around 3000/3500 RPMs, AFR drops to 12.
But as I go higher on RPMs, the AFR goes higher and higher too. And that is not normal to me.
Moreover, starting at 4500 RPMs, AFR is above 15, and I'm starting getting knocking.
So I stopped immediately pulling on it, and after 30 mins I started getting a Check Engine Light. I was in traffic inside London at this moment.
The next day, I got the car back home from the UK (a trip that was about 700 km), all the way below 3000 RPMs to avoid the boost kicking in.

Once back home I immediately checked the error codes with my OBDII device :



In english :
"System is running lean (group 2)"
"Random misfires detected"
"Misfire on cylinder 1/2/3"

I removed all the error codes, as I thought they were logged the previous day, when I tested the car.
Then I moved the car from my home to its parking place where it usually stands, in my office, located about 40km away.
All the way below 3000 RPMs, no error code during the whole drive, then I got to the parking place... Then I got the light again, as the car was idling.
Idle was a bit instable, small vibrations, but nothing compared to the one I had with my dead coil last year.
So I checked the error codes again ...



Basically, the same codes I had the previous day.

I immediately spoke about that to the guy who made the installation. He told me I have most likely issues with my coils as the only ones that would really do it are Lexus OEM ones. He also told me not to worry about the AFR going higher with RPMs, and that this is normal as the engine needs more fuel to operate. I do believe that in good conditions, AFR never goes above 12. Moreover, the error codes are just confirming that my system IS running too lean...

First question, can someone confirm that the OEM mapping actually CAN compensate such a difference in the air intake pressure ? Apart from this, if the OEM mapping is supposed to compensate it right, I have several ideas about what can cause this - I do believe I must have an issue with my fuel system. Most likely my fuel pump or my injectors dying. It seems there is no fuel filter on the IS200 except the small one located on the fuel pump. So I presume the first step would be to replace the pump. Then have a look on the injectors.
I also think I'd have better upgrading my spark plugs for colder ones. As I'm getting into a consequent setup adding a turbo, it's normal that I need to upgrade the main elements - plugs, fuel pump, injectors.

What are your thoughts regarding these issues ?
Has someone experimented such trouble like the ones I have ?

Thanks a lot in advance,
Alex