PTYIS2

Im using Techstream to gather live data list of the engine ECU. There is a set of parameters for misfires. while accelerating those parameters are clear, but when decelerating the "Cylinder 7 Misfire Count" and "Cylinder 8 Misfire Count" start adding up maybe up to 2 or 3, then it clears and if i repeat the process it will do it again. At the same time you can hear little backfires coming from the exhaust only when decelerating .

The strange thing is that tech stream is not sending a DTC at all, additional the CEL is off too. Is this normal? maybe the misfires are so small, for now, that its not triggering the ECU to throw a DTC. For now the plan is to check spark plugs, although just got changed 3 month ago, and switch coil with ones from other cylinders to see if misfires go to those cylinders and then if thats the case, ill need to replace the coils. I was wondering if it might be carbon buildup.

Thoughts?

JP

lorenr

iTrader: (1)

Run some engine cleaner through the fuel tank. Chevron makes a good one.

Check the coil connections on seven and eight. I used a tiny bit of "bulb grease" or contact cleaner when I reconnect coils. Be sure the plugs are not coated in oil from a valve cover spark plug seal leak. I would check the firing order, but believe those cylinders are at the rear of each cylinder head. If you have a lot of miles on the car, you could be losing valve cover seals.

I would then start switching coils. By the way only replace the two coils in question, not all eight.

Loren

PTYIS2

Update: I talked to the services manager at the dealership yesterday. He said since its not showing CEL or throwing a DTC i should not worry, They dont believe theres a problem with plugs (were replaced on december) nor the coils since the car just have 10,000 miles. They think is carbon buildup. Told me to stop by and they will run the techstream test themselves.

Jp

93MSB

iTrader: (8)

Has anyone else experienced these symptoms?

I've been monitoring via techstream for a couple days looking at these misfires that do not trigger a CEL. I've seen individual misfires at random times on cyl 2,5,7,8. I don't have any firm observations of any trends yet, but they do seem to be more common after deceleration and after the car has warmed up.

My car has 145k
original coils
DENSO 4705 spark plugs ~20k miles of use (denso compatible plugs with smaller gap and larger center electrode)
i have run bg44k through the tank within the last 10kmiles
valve cover gaskets were replaced in late 2020

Dattaboi

This was what RR Racing discovered with my car:

https://www.clublexus.com/forums/is-...ar-thread.html

93MSB

iTrader: (8)

We're you getting misfires on random cylinders? and how frequent were your misfires on cyl 8?

I dont think my valve is damaged at this point. The guy from russia who said he saw several valve failures mentioned the misfire would be very persistent on the effected cylinder. My last two drive cycles I had no misfires, only difference is a lower ambient air temp.

Dattaboi

I don't think your valves are damaged either. I think this is more of a prompt to get all your services up to date, particularly the valve adjustments. I was getting misfires specifically in cyl-8. When I first noticed the misfires, I had finished repairing valley plate leak. This didn't trip a code but it was noticeable at idle and wot. Later down the road, I replaced all coil-packs and spark plugs - noticing spark plugs 8 and 6 were fouled. This prompted a compression test where we noticed cyl 8 was down to 90psi. The car was then sent to Rafi to rebuild the bottom end - where his discovered the valve as it sat.

The vehicle was serviced with Lexus its whole life - and looking back at the infostream service history, no valve adjustment services were ever completed on the vehicle.

Not sure if this helps any, hopefully in narrowing down/eliminating causes.