1990 xj40 dual exhausts?

I've been under the car a few times this past week, patching a small exhaust leak and doing other repairs, and I'm sort of wondering about the design of the exhaust system.

One would think from the two pipes out the back that this car has a "dual" exhaust system. It does have a split manifold - three cylinders each into two manifold exits, but then I guess it y's into a single pipe because from below there is a single pipe with the oxygen sensor mounted on top.

Then it splits into two again with a real noisy - read power-losing - y-pipe with a couple of larger chambers under the passenger compartment, then pipes past the rear axle to larger mufflers just in front of therear bumper. This y-connection was a tad noisier thanstock, as I have just cemented up a small hole right where a shroud mounting bracket was welded on to the pipe just behind the y. If I ever take the exhaust right off I'll weld it up, but for now the "bubblegum" repair works just fine.

There are two layers of shrouding on my vehicle, both laid on top of the middle section. I suppose whoever worked on this car in the past couldn't, or didn't for some reason, bolt these together one above and one below the middle section.

Those larger chambers in the middle - are they the catalytic converters, or is that the single pipe with the o2 sensor on top, and the offset chambersare merely part of the noise suppression apparatus?

I'm wondering at some future point, when this vehicle is old enough to be acceptable where I live as a "classic" aged vehicle, and no longer requires an emission test, if I can re-plumb it as a proper twin exhaust vehicle again, or will this just be too hard to do? Are there parts available for this? Would I have room for 2 pipesat the section where the o2 sensor is mounted? Will I have to make up some pipes of my own?

Another thing - some where I read (the manual?) that this car has a stainless exhaust system, but the middle section is rusty old plain steel. Is this a replacement that is not up to original factory spec, or is it only the rear section of the exhaust system that is stainless?

Comments welcome.

- Tom

 

Not stainless from the factory. You would have to make your own exhaust system. It is illegal to remove or disable any factory mounted emissions system.

Sorry about all the bad news.

 

From another forum I have learned that the catalytic converter is the rear-most of the frontal, single-pipe sections, so replacing this and the 2-into-1 pre-converter section in front of it with a dual setup back to the mufflers shouldn't be too difficult for a good Midas Muffler pipe-bender. The mufflers are plain steel in a dual pipe system, and everything back of that is stainless - pipes, resonators clamps and brackets.

Perhaps in your country, Ken, replacing anything is illegal, but further north anything over 20 years old is a "classic", and in some provinces no longer subject to emission controls. I'm not sure if this means you are still not supposed to replace them with something different, but I'll find out.

What I am more concerned about is what effect this might have on the function of the oxygen sensor, and whether this sensor's output is used solely for the ECU to control mixture at the injectors, or if it figures into other controls also.

Thanks,and your news was not all that bad, hahaha.

- Tom

 

No real effect to the 02. It is solely to adjust mixture.

 

There are four catalyst on your car first 2 small ones on the downpipe and then 2 Bigger ones under the car. not the ones right before the axel but the ones before them

And you should always let the exhaust cross att some point to get the same amount of backpressure for all the cylinders