P0138
 

About a week ago I noticed that my 96 1500 with 5.2 kinda stumbled as I took off on a hill. Didn't think much of it because it ran fine afterwards. Then I noticed it was blowing black smoke out of the tailpipe. It wasn't just a little smoke either. So I do some digging and come to the conclusion it's either the coolant temp sensor or o2 sensor. It's not the coolant temp sensor, so I check codes. Come up with p0138 bank 1 sensor 2 high voltage. Would the rear o2 sensor cause it to smoke like that? Always thought it was just for catalytic converter efficiency.

Just swap them both with new NTK jobbers and call it good!

There was a recall on the cats in 96, They break up inside. If it wasn't replaced get a magnaflow cat with NTK 02's then you will be good. It's what's in mine and no issues.

So the rear o2 can cause it to smoke?

Not really. The rear O2 is basically just to monitor the cat. It has some small effect on mixture, but, not much.

Ok. That's kinda what I thought. So now to figure out what's causing it.

How much should o2 voltage swing? The front goes from .05v up to 1v. It does the sweep in about a second I would say. Rear stays at 1v.

Generally from 0 (.05 is close enough....) to 1 volt. .5 is a perfect mixture.

I think you have issues with the rear O2..... Would be interesting to check the signal return voltage, and see what it really is.

It has an exhaust leak right after the cat and has had for a while. If I delete the cat what do I need to do for the rear o2?

O2 fouler? Fooler? Something like that. It's a bung extension that moves the sensor further out the pipe so it still reads a different mixture. Enough anyway.