O2 Voltage

[Ramz2015]

First of all I must say thank you for all the valuable information on this site.

2015 Ram 5.7, 8 speed Transmission 33k miles

During cold start the tach show a rough start but go away after idol came down. Some time later I noticed the tach jumping around slightly at highway speeds. Then I noticed it was also jumping around in the parking lot at any RPM between 1200 and 1800. Rough run can be heard in the exhaust. No codes have been generated.

Took to dealer and flashed PCM. No change
Changed plugs and ignition coils. No change
Installed Diablo Sport T2 Platinum with new PCM. (Best choice ever) Started watching all 4 of the O2 voltages. Bank 2 upstream and down would warm up nice and evenly. On Bank 1 upstream and downstream the voltage is jumping all over the place! 35 mv then 820 back down to 300 and so on. When they drop the engine runs rough.

So I replace driver side upstream and swap the downstream with passenger. No change. Still no code!

What connects both the O2 sensors on Bank 1? Does anyone know where they are grounded? Maybe a relay?

Thanks for any advice

 

[CVX20]

Vacuum leak maybe?

 

[Fast69Mopar]

Upstream oxygen sensors are not steady. They switch from low to high, lean to rich and back and forth. That is how they control the fuel. The Downstream oxygen sensors are supposed to be as stable as possible. They monitor the catalyst efficiency and aid in long term fuel correction hence the Long Term Fuel Trims.

If the upstream sensors are not switching lean to rich fast enough it can cause the engine to run rough. If they stay lean too long it starves the engine of fuel on that bank. If they stay rich too long it will over-fuel that bank.

Does the 1/1 and 1/2 sensors switch low to high pretty evenly or is one slower than the other?

 

[Ramz2015]

Thank you Fast69Mopar.

I reached out to Diablo Sport to verify I am reading the gauges correctly to develop your theory. According to Diablo Sports these are the sensor identification for each O2 sensor

O2S11 driver upstream
O2S21 driver downstream
O2S12 passenger upstream
O2S22 passenger downstream

Both the passenger sensors stay with each other. The driver side are all over the place. I will try to upload a video I took this morning. Also, this weekend I am going to purchase a temperature gun and take temperature of the CAT’s to see if there is a difference.

Also, when de accelerating all gauges go to 0.

 

[Ramz2015]

Can’t upload a video so here are two different pictures. O2 gauges are located in the bottom right corner. Engine temperature is 199 truck had been running for a good 25 minutes before these pictures were taken

 

[Tach_tech]

According to your 2 pictures both the pre cat o2 sensors are switching normally and the post cat are remaining fairly stable, so based on those 2 pictures there’s nothing really wrong.

It’s really best to graph them over awhile though and monitor for any irregularities.