2015 5.3 Trans rebuild engine issue

Adam Ferguson · June 25, 2020

So I had my Trans rebuilt. When the builder test drove it after rebuild he left a o2 bank 2 sensor unplugged. He Drove it for a few miles before truck stared running bad, idling bad, smoking and threw p0300 misfire code. I think this was because it ran really rich because of the missing o2 on one side. We have changed the plugs they were wet as can be. It idles better but still smokes and low on power. Still has p0300.

Next steps are to change all four o2 sensors. I think I might have to replace the catalytic converters as well due to over fueling. I think this is the power issue.

Question is anyone ever experience this or feel like it could be something else?

CamGTP · June 25, 2020

An unplugged o2 sensor will not cause all these problems. Something else is going on here.

If an o2 sensor fails (or unplugged) the computer will just revert to in simple terms a pre-made air/fuel calibration that will be good enough to get you somewhere. The computer is not going to start dumping in extra fuel because a sensor died or didn't get plugged in. If a sensor was failing and started reporting incorrect readings while plugged in, then that could cause a problem with a lean or fuel mixture but if the sensor was not even there it can't get a reading off of that bank to do anything.

P0300 means multiple cylinders are having a misfire. A scan tool will let you pinpoint which cylinders to look at to help further figure out where to look. You can also use a scan tool to look at fuel trims to determine which bank of cylinders the issues might be on as well. And you can look at the o2 sensor operation before you possibly waste $200 on new sensors.

carnau · June 25, 2020

17 hours ago, CamGTP said:

An unplugged o2 sensor will not cause all these problems. Something else is going on here.

If an o2 sensor fails (or unplugged) the computer will just revert to in simple terms a pre-made air/fuel calibration that will be good enough to get you somewhere. The computer is not going to start dumping in extra fuel because a sensor died or didn't get plugged in. If a sensor was failing and started reporting incorrect readings while plugged in, then that could cause a problem with a lean or fuel mixture but if the sensor was not even there it can't get a reading off of that bank to do anything.

P0300 means multiple cylinders are having a misfire. A scan tool will let you pinpoint which cylinders to look at to help further figure out where to look. You can also use a scan tool to look at fuel trims to determine which bank of cylinders the issues might be on as well. And you can look at the o2 sensor operation before you possibly waste $200 on new sensors.

Exactly. You're not having an 02 sensor problem. I have an idea of what you have going on though. I have seen this several times when people get their trans replaced. They will bring them to the dealership after they have been replaced with exactly what you have going on.

The wiring harness to the High pressure fuel pump and the injectors are underneath the manifold and they run over the back of the engine. Sometimes when the transmission is reinstalled it will pinch the harness between the engine and the transmission. This will cause a P0300 and a reduced power concern.

It could have been disconnected by accident when the transmission was removed as well.

Start there IMO