My 2007 RX is throwing a cylinder 6 misfire code. CEL came on for a few days, turned off, and then came back on. Car runs fine, no shuddering/sputtering under accel/decel. All 6 spark plugs were replaced 12 months ago and the cylinder 6 ignition coil was replaced 9 months ago. Mechanic took a look and it's not a faulty plug/coil, but the compression in cylinder 6 is low (~120).

He noted that I could replace the fuel injector in that cylinder, but that he doesn't believe that is the culprit of the misfire/CEL, due to the low compression hovering right around the range where it would throw a code.

Off the top of my head I could do the following:
- Replace fuel injector and see if that takes care of the issue. I debated having him swap injectors with another cylinder to see if the code travels with it, but at that point, I'd just pay to have him replace it with a new one since the labor costs would effectively be the same amount.
- Valve adjustment - Is the cylinder 6 in the front or back bank of the V6?
- Headgasket replacement - Mechanic friend thinks it could be an overhead cam, but is just spitballing based on what I've told him. Mechanic quoted ~$4K for the job, would rather not spend that much money upfront right now. If necessary, could eat the cost, but would look at purchasing a newer car at that point.

I'm going to take the car home, clear the code and see if the situation gets worse over the next few weeks, but wanted to see if anyone had run into something similar before and could share some insight.

Thanks

 

Good news, cylinder 6 is next to trans and the radiator (front right when looking under the hood from front of car), easy to pull plug, and get a borescope in there.

There is no way to adjust valves, they use mini hydraulic lifters with rocker arms, but they can get stuck but seems very rare.

While waiting for your car check this: https://www.clublexus.com/forums/rx-...oking-for.html

 

Thank you sir. Mechanic did mention that we could potentially adjust the valves, but that he doesn't think it's the issue since I'd be getting multiple cylinder misfire codes if the valves were off. He did check it out with a borescope and mentioned that cylinder 6 wasn't a perfect circle and that's most likely what's causing the low compression/CEL.

 

Mechanic is wrong, valves are not adjustable. Piston not round? Don't believe it, get another mechanic.

Is this the 3.5L 2GR-FE engine?

 

Not a perfect circle? Peculiar statement from a mechanic. Scored? Yes Oil? maybe – not round? kind of odd