I've been getting a recurring check engine light on my '06 V8V for about a year now. Always the same to cylinders (4 & 7) )(P0300, P0304, P0307).

At first I thought it was the plugs or coils. I troubleshooted those to no avail.

Then I thought maybe just due to infrequent use, i increased my driving cycle quite a bit for about a month with no change.

Most recently I decided to take a look at my O2 sensor readings. 3 of the 4 all look fine, but S2B2 is running rich (indicated by a fluctuating, but steadily high voltage level). I did troubleshoot the sensor and that doesn't appear to be the issue. So far this is the only thing outside of the misfire that looks like a potential culprit. I'm not seeing any obvious leak paths in the hoses. I verified that the fuel rail pressure is good.

Any thoughts suggestions on a next step? Any help would be greatly appreciated.

 

if there are multiple o2 sensors, i think i would switch positions of the o2 sensors (i don't even know if this is possible) and see if the readings point to a different o2 sensor. this is just a guess. i don't even know what a S2B2 (sensor 2, bank 2?) is. good luck.

 

Thanks for the suggestion. S2B2 = Sensor 2 Bank 2. It is the same as Sensor 2 Bank 1, but I've already done troubleshooting on the sensor. It is giving an accurate reading.

 

i would still try swapping it out (assuming it's worth the effort if successful and the problem is intermittent) with one that appears to be healthy. my reason being that, as an insufferable pundit might say, the utility of bench testing is inversely proportional to the intermittency of failure.

 

I'd probably replace one of the O2 sensors, they are only about $80, if you buy genuine NTG / NGK sensors, not AM branded ones. In the UK they are readily available on ebay.

Its usually the ones closest to the engine that go first, but with an '06 your front ones may have been replaced?

If you're having a problem with cylinders 4 and 7, that won't be your o2 sensors, most likely its plugs or coils

 

Thanks, the plugs/coils were the first thing that came to mind. They and their gasket seals were replaced a little over 2 years ago. That said, I still swapped the coils/plugs with other positions and the misfire did not follow them (i.e. the original cylinders still misfired).

The B2S1 O2 sensor was replaced in a Jan '18 right before I purchased the car. It was actually throwing an O2 sensor fault (P0153) at that time.

My current suspension is that whatever is causing the misfire is happens to also be driving the rich reading.

That said, i still need to find some time to swap the S2 sensors to verify that the abnormal reading doesn't follow the sensor.

 

Question, did you disconnect the battery and re-learn the misfire corrections when you originally replaced coils/plugs? Does it actually feel like it's running on 6 cylinders? If it is an actual misfire you are going to have rich condition on that bank because of the unburned fuel.

 

Yea, I've gone through the misfire correction routine a couple times over the past year (verified via a Foxwell reader). When the misfire occurs under moderate to high acceleration the engine does run rough and at reduced power. I've gotten new misfire cautions when just cruising or low acceleration as well, in those cases there wasn't an obvious performance difference, presumably because i was already so far down in the power band.

 

Update. I did finally swap the O2 sensors from B1 to B2 as a double check on the sensor. The reading did NOT follow sensor, so the rich reading seems valid.

 

Did you swap both upstream and downstream sensors? How old is your air filter? Check the MAF? Could be wiring related too. It could actually be running rich, which might be injectors, but probably not.

 

I know it feels very old-school, but how do the plugs look? Are they sooty on the bad cylinders? or a nice brown colour?

 

I only swapped the downstream sensors sense the S2 was the only one that appeared to be giving anomalous readings. That seemed pertinent as it also decoupled the pair.

The air filter was about 5 years old. It only had about 10k mi on it, and was visually about 60% through its life. That said, i went ahead and replaced them, to no avail.

I did check the MAF, I don't have a good way validate the value, but it is generally responding appropriately.

Any thoughts on how to double check the injectors? For whats worth, below are a few fuel system related values that i pulled from my scanner:
Throttle Position 22%
Engine RPM 3417
Short Term Fuel Trim Bank 1 - 13.3%
Long Term Fuel Trim Bank 1 - 5.5%
Short Term Fuel Trim Bank 2 - 21.9%
Long Term Fuel Trim Bank 2 - 5.5%
Intake Manifold Pressure - 7.7 psi
Ignition Timing Advance #1 Cyl - 25deg
Fuel Rail Pressure Rel - 55psi



The plugs looked used, but still good. I also swapped the coils and plugs with all of them going to different cylinders which didn't change anything.

 

Thanks, I'll take a look through those.

 

After putting the first few hundred miles on my BRAND NEW motor I got an emission system service required light too. Took it back to the dealer and it's reading the same codes with a misfire on cyl 8. They're starting with plugs but of course the master tech had a covid scare so service dept got shut down for a week. Luckily everything should be covered under warranty but I'll keep you posted on what they find.

 

The new motors are completely different from my '06. That said it is a bit disconcerting that they still continue to have similar issues in this area.