MarPov95

Good evening, I apologize in advance for the rather long post.
I have a 2008 Lexus Ls460. The car was not running properly when I bought it. It would barely move out of the driveway. Was getting random misfire codes for several cylinders on bank 1. (DRIVER SIDE) I changed all 4 of the ignition coils on bank 1 with Denso coils and changed all 8 of the spark plugs as well. While I was doing that I noticed oil in the galleys so I changed all of the spark plug seals with new seals from Lexus as well.
The car drives great and goes down the highway wonderfully, it still however sputters under load & then throws codes for misfire 5&7.
I swapped the coil packs from cylinders 5&7 to cylinders 6&8 and the codes remain cylinders 5&7 misfire. No change.
This morning i decided to swap the injectors from 5&7 to 1&3 and drive it again. Still misfires 5&7.
I plan on doing a compression test, but as good as this car is driving, I cant help but feel i am missing something simple. Any advice would be appreciated.

Boykie

Use borescope to check 5&7 inside. If there's oil - that's your misfire. If not - I would check injection system (direct one).
Coils rarely fail on UR-FSE. What's the condition of plugs in 5&7?

MarPov95

All 8 of the plugs are brand new denso plugs, as stated above.

Boykie

I meant ones you took out first. Oily/rich/lean cylinders foul plugs.

MarPov95

Apologies, my misunderstanding. Pretty heavy carbon buildup on those.

Boykie

So, different from all other 6? Ok. Borescope is ideal to check 5 and 7 now. Is there oil inside the intake manifold (some is ok, lots is pcv is dead). Also suspected valve stem seals and/or sleeves failure. What oil is used? OCI? Mileage?

MarPov95

No they all appeared to be the same buildup. Originally the car would hardly move. Changing the coils solved that problem. Changed plugs just because and all 8 were essentially the same.
Driven the car around 1500 miles. Not smoking or using any oil. I forget what's in it right now but always changed routinely. 155k miles.

miket000

I'm curious what you find. I had the same cylinders misfire under load. I hooked up an air compressor into the cylinder 5 spark plug hole to pressurize the cylinder (80psi). At times the coolant tank got air bubbles during the test( head gasket leak). Cylinder 7 didn't push any air out. Misfires were not as bad on 7.

I picked up another LS recently it also shows initial signs of a misfire developing, same bank. I don't recall which cylinder. It's not bad enough to feel or throw a cel but I can see the Misfires in techstream. Only during start and while flooring it. I'm thinking head gasket on this one but it may be worn valve guides.

MarPov95

I went to the dealership today and paid them to do a full diag. They informed me that the catalytic converter on bank one had been cleaned out although not well. They said that the y pipe was clogged and needed to be changed to the tune of $6600.00
of course I didn't let them, but apparently I have a clogged catalytic converter and ypipe.

I'll be looking into this more.

Gerf

I don't think that would be the case if your exhaust was clogged, it might be worthwhile to remove the air filter housings and check the port injector connectors just in case there has been a previous engine repair and some locks were snapped. It's a quick check

swfla

iTrader: (1)

I've seen several mentions of lacquer thinner used to clean catalytic converters on YTube. I don't know much other than that. If it works and is safe, seems a cheap and easy way to improve your cat converter situation. As it goes into gas tank, it would also clean entire fuel system and the top and direct injectors.

MarPov95

I took the injectors off and swapped them around during diagnosis. code remained 5&7. Doesn't appear to be any issue with those injectors.

Boykie

Before believing that 'diag' please swap MAF sensors and see if misfire moves.
As to injectors - under load top ones are mostly off. Direct ones deliver all power.

swfla

iTrader: (1)

Excellent point about which injectors provide the fuel under throttle. The MAF swap is smart.

MarPov95

I have cleaned the MAF's but i havent swapped them out. I will try that. Simple enough. Would MAF cause only 5&7 to throw codes?