Help sought with diagnosing high right bank O2 sensor voltages.

[seven30]

I could use some input on tracking down an brand new O2 issue.

Truck starts fine but as soon as it warms up and goes closed loop it runs poorly and eventually sets mil light.

I thought I got hit with the oily downstream right side O2 sensor issue. Code P0137 and 0300. B2/S2 was very oily so cleaned it well with contact cleaner and shop air and cleared codes.

But now graphing all four O2 voltages, the left side looks normal hunting low/high but both B2 S1/S2 right side are high ~0.82-0.88. However if I punch it, on decell, all four sensors briefly go to 0.0V as they should suggesting they are all working.

Another data point: under load right bank O2 hardly changes.

I do have a permanent P0171 however I disconnected both right bank sensors at one point just to see if it affected voltages which it did with both registering 1.275V while disconnected.

What could effect just the right bank and make O2 sensors read high/rich? EGR? VVT? EVAP?

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[Hootbro]

What could effect just the right bank and make O2 sensors read high/rich?

Intake manifold leak on just that side letting unmetered air in.

 

[Greg_L]

Intake manifold leak on just that side letting unmetered air in.

Possible. Are Jeep intakes a common plenum or individual runners? It would have to be a leak at a specific Bank2 cylinder most likely.

 

[Hootbro]

Possible. Are Jeep intakes a common plenum or individual runners? It would have to be a leak at a specific Bank2 cylinder most likely.

It is two piece upper and lower intake design. Unsure of the plenum design.

 

[Greg_L]

It is two piece upper and lower intake design. Unsure of the plenum design.

Ok so to me, without ever having been inside one, it looks like a vacuum leak would probably have to be isolated to the lower half of the intake for it to affect one whole bank..

OP....with the engine running, spray carb cleaner around the base of the lower intake and the joint where the upper and lower intake halves meet. Listen for the idle to change as you spray the sealing areas. If you hear a change, that area is where a leak is happening.

 

[seven30]

Intake leak was one of my initial thoughts however, it idles fine when cold until the closed loop mode is enabled. Also at high throttle when an intake leak contribution is minimal the sensor is still logging .840 to .860. Keep in mind a high voltage indicates rich plus, when coasting with no throttle and fuel cutoff all the sensors register 0V. Why is it logging a P0171 lean when O2 voltage indicates a over rich exhaust. The oil soaked downstream sensor connector has been cleaned several times.

 

[Greg_L]

Intake leak was one of my initial thoughts however, it idles fine when cold until the closed loop mode is enabled. Also at high throttle when an intake leak contribution is minimal the sensor is still logging .840 to .860. Keep in mind a high voltage indicates rich plus, when coasting with no throttle and fuel cutoff all the sensors register 0V. Why is it logging a P0171 lean when O2 voltage indicates a over rich exhaust. The oil soaked downstream sensor connector has been cleaned several times.

That's not over-rich at high throttle. The O2 sensor reads after the fact. Other sensors also aid in determining the mix. Maybe the O2 is showing rich only because the CPU is dumping fuel due to other factors. If the O2 is performing normally you gotta keep looking upstream. There's about a dozen other things that can create a lean condition.

 

[seven30]

That's not over-rich at high throttle. The O2 sensor reads after the fact. Other sensors also aid in determining the mix. Maybe the O2 is showing rich only because the CPU is dumping fuel due to other factors. If the O2 is performing normally you gotta keep looking upstream. There's about a dozen other things that can create a lean condition.

At full throttle all four are around .84V and at decell all four are at 0V. But idle or cruise right side is still at .84V. Making it even stranger is the P0171 lean code. The O2 is reporting rich but PCM is thinking lean so its trying to enrich the right side. AFAIK the O2 sensors are all the PCM has to determine mixture ratio so its an intriguing problem. I wonder if the PCM has gone bonkers.

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