Lexus gs450h engine misfiring - p0390 code help

jeepass · December 25, 2022

Hi,

Im wondering if someone had a similar problem knows what could be the reason for the sudden misfiring of the engine in lexus gs450h. The failure occurred suddenly at a speed of about 50mph the engine suddenly lost power and began to work unevenly as if was misfiring. It sounds like a diesel now...

The car was towed to a mechanic, hooked up techstream and error P3090 Camshaft Position Sensor 'B' Circuit Bank 2 popped up. The mechanic said that maybe it was the spark plugs and not the sensor and replaced all the plugs, but the problem remained.

The sensor will arrive after Christmas and will also be replaced, but I do not know what to do next? The mechanic said that it could be a pulled timing chain or jumped one tooth and he doesn't know really lol

Has anyone of you had a similar problem ? the car starts engine without eny problem but it seems as if it is not running on all cylinders. Mileage is 168k.

What else should be checked to try to remove this fault ? Anyone knows any good Lexus mechanics in Hertfordshire ?

I am attaching a video of the engine running

IS300FSPORT · December 25, 2022

Could be Carbon build up use full tank of V power & get it upto temperature & rev it out old italian tune up may help.

If not see this link below just the wiring came loose from the plug.

https://forum.ih8mud.com/threads/gx460-p0390-code-on-2011-build.1266722/

m4rkw · December 25, 2022

A competent mechanic would never say "dunno" and replace parts on a guess without diagnosing the problem. If you carry on with that approach you'll likely run out of money before running out of guesses. You may well have wasted money on both plugs and a sensor without fixing the original problem.

Take it to a competent technician for diagnosis and go from there.

I always recommend Toyotec in Redhill but probably a bit far for you, I believe @royoftherovers maintains a list of known good Lexus technicians

royoftherovers · December 26, 2022

20 hours ago, m4rkw said:

A competent mechanic would never say "dunno" and replace parts on a guess without diagnosing the problem. If you carry on with that approach you'll likely run out of money before running out of guesses. You may well have wasted money on both plugs and a sensor without fixing the original problem.

Take it to a competent technician for diagnosis and go from there.

I always recommend Toyotec in Redhill but probably a bit far for you, I believe @royoftherovers maintains a list of known good Lexus technicians

Lexus Indie Garages (1).docxLexus Indie Garages (1).docxLexus Indie Garages (1).docxLexus Indie Garages (1).docxLexus Indie Garages (1).docx

Steven Lockey · December 27, 2022

Sounds like that guy completely ignored the error code and tried to treat it as a misfire. I believe there
is a different error code if its just misfiring. May have just been attempting a quick fix without researching
it as I can't see how a camshaft position error could ever happen due to faulty spark plugs.

The other suggestions seem sensible, I think replacing the sensor is a sensible first step as the other possibilities
are expensive.

jeepass · December 30, 2022

Hi all,
many thanks for you replies.
Camshaft position sensor B has been replaced with no good results, also tested all ignition coils and they work good.

Checked all connectors and they were ok as well.

I know good mechanic would just replace parts one buy one a do a guessing game but I even called Japex who do repair loads of japanese cars and they said if its timing chain they dont want to do it an sent me back to lexus but they say to repair all timing kit will cost as much as this car is worth so no worth doing it.

Steven it was just this code as i used techstream to see any other codes.

May call Toyotec and see what he says.
Used my endoscope and suspect stretch/worn timing chain on VVT sprocket as it looks very loose or tensioner went bad
The place where i use my endoscope is highligthed in yellow on one of the pictures.

Really dont know what to do, may sell is as it is or do breaking and sell parts only

got also a video when engine is running so if any of you is good with diagnostics you can see the stats while the engine is running.
its visible on video that misfire count is rising while im reving up engine.