Test Pipe and Oxygen Sensor Install on QV

I had a good experience with my '84 QV this weekend. I'm planning my trip to the 2018 International Meet and was concerned about how my car was going to hold up a long drive plus what sounds like quite a bit of track time. I have had the "Slow Down" light (SDL) come on once before, although at fairly high speed. I was worried that a few laps on track was going to lead to the same result.

My car is registered vintage and is thus emissions exempt in my state. So I decided to try a "test pipe" set up rather than chase down a high-flow cat. I ended up buying this unit from Top Speed Auto in Texas for $170. It's not a work of art, but it was certainly solid enough. I have seen better welds, but this is really not a factor given that you can't see the thing from above or below. Basically, nobody cares. It has proper fittings for the temp sensor and the O2 sensor. It came with bolts and gaskets.

I also bought a new oxygen sensor. I got the NGK on Amazon. It came with anti-seize already on the threads. The fittings were a perfect replacement on both ends.

To get to the cat, you have to remove the rear bumper, the splash shield underneath, and the diaper that covers the exhaust. The cat is held in place with three bolts on each flange for a total of six. The top bolts are a bit hard to access, but by no means impossible. You can remove the cat with the muffler in place.

I swapped in the new test pipe, fitted the temp sensor with a bit of anti-seize, and fitted the O2 sensor. Remove the upper and lower halves of the airbox and you can see the electrical connectors. I separated them, and taped a piece of scrap wire to the connections and then pulled the wire down through the bottom. The O2 sensor wire is clipped in behind metal tabs in two places, so you need reach around and feel your way to get the wire out. When you pull the old sensor out, tape the connector end of the new sensor to the piece of scrap wire and pull it back up to the top. Dielectric grease the connectors and replace the airbox. The new O2 sensor has a smaller diameter body and the original heat shield that clips to the sensor will not hold on the new, smaller sensor. Since I am anticipating lower temperatures with the cat gone, I decided not to sweat this.

Reassemble everything, and now for the results:

The exhaust note may be a slight bit more pronounced, but it's not crazy--at least not with the stock muffler. What I did notice was that power delivery seems much smoother and drivability was significantly better. I don't know if this was just a new (after 34 years) O2 sensor delivering the improvement, but the result was pretty solid for an investment of $170 plus $60 for the sensor.

As always, I saved all of the old parts. The cat was in pretty good shape.

 

Maybe I didn't need to pull the bumper, but my recollection was that the four screws that hold the diaper at the top are behind the bumper. I could be mistaken, but that was my take on it.

The exhaust smelled pretty rich with the cat. It's certainly no worse now and may even be improved by the new oxygen sensor.