killerbyte

I have been having some P0306 errors (misfire cylinder 6) over the last few weeks. It only happens around idle. I did not realize what a pain this whole process has been to change this out. This is what I have done so far:

1) Clear the codes. Of course it came back wih P0306
2) Swapped cylinder 6 coil pack with cylinder 5 (much easier to get to). I noticed a strange brown residue on the coil pack for cylinder 6. Cleaned the coil pack connectors and terminals. Cleared the codes and it still came back with P0306.
3) Replaced the spark plug (thinking that there maybe something wrong with it). Cleaned the fuel injector terminal. Cleared the codes and it still came back with P0306 but engine is running smoother.
4) Used an ohm meter to test for fuel injector 6; reading was 13.9 ohm. Read fuel injector 8 and it was 14.1 ohm.

Is the fuel injector resistance within specification? Should I swap it?
Do you guys believe cleaning the throttle body will help (I don't know if that affects misfires)?

Any insights appreciated.


Thanks.

VVTiBob

Per the 02 FSM the ohm range with car the car at air temp of about 68 degrees is 13.4 - 14.2 Ohms
Fuel pressure should range between 44 and 50 psi at idle. After stopping the motor for five minute pressure should be about 21 psi. If you can check the volume flow it should be 3.7 to 4.5 cubic inches in 15 seconds.

The FSM also suggest these trouble areas: (I'll list them all even though you've already inspected some)

For the MAF measure the resistance between terminals ETHA and THA at the following temperatures:
68 degrees: 2.21 - 2.69 ohms
140 degrees: 0.49 - 0.67 ohms

For the engine coolant sensor ...well there's a large graph based on temperatures range here are a few:
68 about 2 ohms
140 about 0.3 to 0.5
212 about 0.2 to 0.3
These are +/- 1% or so.

Oh and cleaning the throttle body, in place, won't hurt if you follow the directions on can. I did mine last year and did see an improvement in both mileage and motor idle.

killerbyte

Thank you very much! I will go through the other optioons and also see if cleaning helps, and check the MAS and coolant sensor (the issue seems to arise after the car has warmed up and at idle).

Another question:

The enginecode is consistent with a cylinder 6 misfire. Do you (or others) feel this is a red herring? In other words, could this be just a general failure in the overall system rather than specific to cylinder 6? The strange soot on the coilpack of 6 vs. cylinder 5 had me conclude it was specific to 6 but this might be a huge assumption on my part.

Thanks again.

VVTiBob

If it was system wide or multiple cylinder misfires you should be getting multiple error code of p0300. Not one of the 01 to 08 errors.

killerbyte

OK, thank you. I hope this will resolve.

killerbyte

First of all, thank you for providing help in diagnosing my car.

After my weekend mechanic stint and having reality set in (i.e. I cannot play as mechanic for extend periods of time), I decided it was time to visit my Lexus dealer to address this for me.

The problem was far more serious then I had imagined. The dealer had to strip the head off of the engine, call the North America Lexus HQ to help diagnose the issue. Long story short, there was a mechanical failure which the dealer said they have never seen or heard before. The car was out of warranty by 5 thousand miles and about one year, but I am happy to report that Lexus has decided to cover the cost of repair in full -- not a penny out of my pocket. Fortunately they gave me a 2011 IS 250 loaner which I have to admit is impressive (reminiscent of my 2005 BMW 330CiC which I owned before). Though I suppose this engine failure should never had happened, Lexus' assistance proved to me that this truly was an exception and that they would accept fully responsibility. I am a bit nervous that my engine will not be the same as factory new. After all, if this truly is a rare event, I doubt the mechanics have had much practice at this work.

I will seek a certified preowned status on the car to insure its long term functionality. Or maybe it is time for a new car. I will solicit interests.

VVTiBob

Glad to hear Lexus stepped up and covered the bill. But you can't just leave us with a "mechanical failure" that no ones ever seen before. I'm really curious what mechanical part of the head failed or misaligned that led to the throwing of a code for one cylinder and no other pointers.
Can you give us any more details?

jasone36

I'm with VVTiBob on this, more details would be quite interesting to know, in case anyone else has this issue.

killerbyte

I did not mean to keep everyone in suspense Things have been quite busy for me.

The dealer claimed a burnt exhaust valve. I had the opportunity to examine the valve and it was not what I had expected a burnt valve to look like. What I saw was a "clean" break, EXACTLY one half around the top circumference where the valve would seat at the head, and with no other signs of damage.

I asked if I could take the valve and they would not let me (as a policy of waranty work). My guess it was sent back to Lexus/Toyota HQ to have it examined in detail.

It was a defect and Lexus owned up to it. I would guess other manufactures would have made me go through the letter writing process to management, or the legal process, but with Lexus they did not and they took full care of me.

VVTiBob

Interesting!

coupdabill

Very interesting,