O2 Sensor Plugs

[kevin bellmore]

Hey everybody,

First Post.

I was hoping someone would have a picture of the after cat O2 sensor plug from a 1998 GMT 400.  According to the pictures on Rock Auto, it is a square 4 pin, but mine is a flat 4 pin and the connector is under a cover on the inside frame rail.  All the after cat plugs look square but mine is not.  Also, how many O2 sensors came stock, and were there two cats and two mufflers and two pipes?  I haven't seen a stock example of one.

[CamGTP]

A 1998 truck is OBD2, there will be two cat converters and 4 o2 sensors on a truck like that. A stock exhaust system should have a Y-pipe that goes into a single muffler with a single tail pipe.

 

Possible that it could have single exhaust pipes back to a single muffler as well with a single exit tailpipe section.

 

Everything I'm seeing is that the upstream sensors are flat and the downstream sensors are square. If your rear sensor is a flat, makes me wonder what someone screwed up doing the exhaust work.

[kevin bellmore]

I will have to get under it again and have a better look.  Whoever cut the cats off left a sensor with the square plug unhooked, but still in the pipe.  I bought a Flowmaster cat that has 4 places for O2 sensors, and it uses one cat with a y pipe and sensors on the left and right pipes, and before and after the cat.  I just need to find where the square plug goes.  

Edited June 30, 2022 by kevin bellmore

[richard wysong]

on my 98 4x4 2500hd,5.7 the front pipe has 1 cat but 2 pipes at the intermediate then another cat in the intermediate and 2 pipes going into the muffler, 1 tailpipe but dual t pipes may have been oe. I have run into the connector problem you are having before and Napa was able to come up with the correct sensor

[kevin bellmore]

I must have been on glue.  The plug on the downstream is indeed a square 4 pin.  But my truck only has 3 sensors.  Left and right upstream and one downstream.  The upstream are 4 pins in a row.

My new cat from Flowmaster has left and right upstream, then one after both of those, a combined upstream, then one after cat.  

Edited July 1, 2022 by kevin bellmore