2005 SR5 V6, Misfire CYL 6, P0306 and P0420

[Texas4run]

Hello everyone,

My 2005 4Runner SR5 V6 started misfiring on Cylinder 6 with two fault codes, P0306 Cyl 6 miisfire detected and P0420 Cat sys efficiency below threshold Bank 1.

I don't really understand how the codes can be related. Isn't bank 1 passenger side?

I replaced the spark plugs and swapped the ignition coil with the same outcome.

Any ideas?

Fuel injector maybe?

 

[Texas4run]

Update!

Ran a compression test, here are the results:

CYL1 200
CYL2 180
CYL3 200
CYL4 180
CYL5 200
CYL6 175

2005 4runner 262K miles. I used a tester from Autozone and had a battery charger connected.

At this point I am leaning towards a fuel issue?

Any input welcome!

 

[OopsIBrokeIt]

Update!

Ran a compression test, here are the results:

CYL1 200
CYL2 180
CYL3 200
CYL4 180
CYL5 200
CYL6 175

2005 4runner 262K miles. I used a tester from Autozone and had a battery charger connected.

At this point I am leaning towards a fuel issue?

Any input welcome!

The 2003-2005 V6 specifically has a flawed head gasket design and the common failure mode isn't the traditional oil/coolant mix or significant compression loss, it's exhaust gas pressurizing the coolant system.

Check if your overflow tank is weirdly full or even overflowing. I'd also pop the radiator cap while things are cold and see if you're full or not. Testing the coolant for exhaust gases is also an option.

I had a vague result on the exhaust gases but clearly had coolant being pushed out of the system when mine went. Replace with the 06+ HG and you'll be good for another couple hundred thousand miles.

 

[Texas4run]

The 2003-2005 V6 specifically has a flawed head gasket design and the common failure mode isn't the traditional oil/coolant mix or significant compression loss, it's exhaust gas pressurizing the coolant system.

Check if your overflow tank is weirdly full or even overflowing. I'd also pop the radiator cap while things are cold and see if you're full or not. Testing the coolant for exhaust gases is also an option.

I had a vague result on the exhaust gases but clearly had coolant being pushed out of the system when mine went. Replace with the 06+ HG and you'll be good for another couple hundred thousand miles.

Thanks for the tip. I didn't see anything abnormal in the overflow tank or the radiator. fluid looks normal and no weird smell. Engine oil looks normal too.

I will try to get a cooling system pressure tester to be 100%.

Thanks

 

[Dave4RCR]

Hey, I’m also chasing a P0306 for a few weeks, no radiator leaks, good compression, changed coils and spark plugs look ok. I found this document that may be helpful for you since you are also having another code along with the missfire.

 

[Texas4run]

Well, I was shooting from the hip and decided to replace all the coils even though it didn't make sense. Maybe they were all about to go bad.

Problem solved! No misfire and no O2 sensor fault code! Car runs perfect again. I am not sure how the P0420 went away but at this point I am just happy the car runs without any issues.