Recently old exhaust on my 91' 3.4L mod. Trooper stared falling apart so I figured that improving gas flow would be the focus of the new system
I just got back from a muffler place with an estimate for whole new exhaust,turns out that for couple extra bucks they can put in a true dual exhaust no problem. I got thinking about it and realized that dual exhaust will isolate right exhaust bank air injection pump.
My question to all you gurus out there is how will this affect functioning of an O2 sensor which will have to stay on the other pipe now cut off from that extra flow of fresh air.

Overall project involves 2" pipes all the way back with the couple of high flow mufflers, no catalytic converters. ( yes I do live in a place where emission control checks are not mandatory just yet)

If there is only one sensor that monitors both exhaust manifolds together and then you cut one manifold off from it to where it is only reading the O2 in one manifold instead of both, you're going to have problems unless you make it where you have 2 O2 sensors (one for each side). Don't know how you would do this and make it work, but that is what you would have to do in order for the engine to work right. The only other solution is to leave the two pipes joining at an H pipe and have the O2 sensor there so that the sensor will be reading the right levels.

Richard

I kind of figured that putting simple H connection will be the only way to make this 02 sensor to work and still have the benefit of dual exhaust.
Thanks for the input though.

Any one else out there with some sugestions on exhaust modifications for Troopers ?

Some guys have run true dual exhausts with two O2 sensors wired to a switch (and using shielded cable) that lets them chose which sensor input seems to make it run better - If all the cylinders are burning the same, it's not a problem sampling the exhaust from only 3 holes. It's not a good idea to run a sensor in a cross pipe, since there will be lag time for the sensor to respond to the very fast changes in fuel trim; warm up time will be increased, and cool-down time (while the engine is idling) will be decreased, and it kinda defeats the dual exhaust purpose (while keeping in mind that going dual on a 6-cyl has less benefit than an V8 anyway). If you went this route, you'd want those sensors as close to the manifolds as possible.

I thought along the same way about dividing the flow of gases in two and so it dosen't really matter if 02 sensor is sensing flow from six or just three cylinders provided that burn is the same on all. But what about that pesky air ijection pump that must make a hell of a difference.
I'm also not sure how installing sensor in the H pipe would obstruct its proper functioning ?
Help me out guys with some of this exhaust theory <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

Don't worry about the air pump - once you're warmed up and the system is in "closed loop" the pump is completely diverted, for good reason: any extra oxygen would send a lean signal to the ECM and result in an over-rich injector command. The pump is only injecting when the engine is warming up. The non-heated O2 sensors located after the two exhausts collect has always been a bit of a problem, they run so cold that they often quit working when the engine idles for some time (like at a long stop light) and you're left with fixed commands (i.e. open loop and no fuel trim adjust) until the hot exhaust during acceleration heats it up and gets it moving again. Locating the sensor in an "H" pipe would not only make the sensor run cooler still, the whole system works better and responds to the constant fuel trim adjustments (up to maybe 16 times/second) faster if the sensor is kept hot and in a strong exhaust stream. This is why on in-line engines it's right on the manifold at the earliest collection point, not the pipe.

The o2 sensor senses percentages, not quantities. So it isn't looking for 6 cyl's worth of o2, it is looking for x% o2 in the exhaust. Several aftermarket headers (including one of the 2 for the Isuzu 4cyl) have the o2 sensor on one port, whereas the stock exhaust because it combined early and there was a convienent place for it after they combine.

I have a picture of one such header at: http://tad.grosvenor.org/gallery/display.cgi/72/DSC00007.jpg

I'd say if a dual exhaust is important to you, the o2 sensor shouldn't be a big concern. Just don't move it so far away that it isn't heated up properly.

-Tad

Thanks for all the feed back guys, this as usuall has been an educational experience, just like my old motto says: "learn from the mistakes of others, you won't live long enough to make all of them over your self"
I'll drop a note on the results once the new exhaust is in. <img border="0" title="" alt="[Smile]" src="images/icons/smile.gif" />

</font><blockquote><font size="1" face="Verdana, Tahoma, Arial, Helv, Helvetica, Sans">quote:</font><hr /><font size="2" face="Verdana, Tahoma, Arial, Helv, Helvetica, Sans">Originally posted by ElBarto:
<strong>I kind of figured that putting simple H connection will be the only way to make this 02 sensor to work and still have the benefit of dual exhaust.</strong></font><hr /></blockquote><font size="2" face="Verdana, Tahoma, Arial, Helv, Helvetica, Sans">In a true dual, performance exhaust, you would want some sort of X or H pipe, aside from the whole O2 sensor deal, its purpose is to equalize backpressure between left and right sides.

-Rob