1990 6 spd Coupe
Had a problem Thursday night on the ride home. Took a hard left turn and hit the gas and she bogged down and bucked. Read a few articles on similar occurances and started with the fuel filter as I had run out of gas a couple of tankfulls ago. I had about 1/4 tank left so I filled up with fresh gas and added a bottle of V Tec. Replaced the fuel filter but she bogged right down when she warmed up. We're going to replace the precats (maybe) and catalytic converter. The codes it threw were showing a rich mixture.A physical inspection led to the conclusion they needed to be replaced. Can the elimination of the pre cats throw off the readings from the front 02 sensor or will it function fine without them?

Looks like I'm about to join the cats for cars club.

the precats are a joke. All they do is restrict the exhaust and kill performance... oh, and they help a little with cold start.

removing them will do nothing for anything.

Read This Thread about my idea for a perfect early C4 exhaust.

Are there O2 sensors before the precats?

I have a hard time seeing how an O2 sensor AFTER a cat can ever be used for feedback to control the air/fuel ratio since the cat has already messed with the available oxygen in the pipes by burning more of it off.

In my experience, these sensors after a cat are only used to compare with the pre-sensor to determine if the cat is bad, they do nothing to effect drivability. And just the same, removing a pre-cat shouldn't affect it either, except for throwing codes.

The O2 sensor is before the precat. no issue at all.

So yeah, if your front O2 is reading rich, it has absolutely nothing to do with any of the cats. Replacing any of them would be a waste of time and money.

It's running rich because the computer is dumping too much fuel for some reason, or because one O2 sensor is off, and the computer can't keep both happy?

^^So as cheap and easy as it is to replace, should He just get an O2 sensor an pop it in to check your theory?? I would guess yes, but I'd like to hear the answer from elsewhere as I am not sure.

Some cars have seperate codes for each O2 and they can be checked by simply swapping them out. Or if it has front rear O2s of the same p/n, swap those and see if the code changes.


I think that "Check Engine" light should actually say "Check Sensor" because the engine is usually fine (until a sensor starts feeding it bad information)

the L98 has only 1 O2 sensor.

did you ever find your problem? If so what was the solution?