Bad exhaust smell. What to do?

[MinnesotaPower]

My 03 Nissan Pathfinder emits a strong odor when I start it cold, and it's gotten worse with time. If I roll down the windows or open the door, the fumes get trapped in the cab and it smells toxic (kind of like varnish). I've had two mechanics look at it: Mechanic A said he'd replace everything from the resonators back, but said not to worry about the sensors or the cats. Mechanic B said I need to replace everything from the resonators back and the rear O2 sensors, but he said "the catalytic converters are fine."

I'm puzzled, because it seems neither fix would actually eliminate the smell. Wouldn't it still just come out of the tailpipe? Wouldn't replacing the cats help filter the exhaust emissions? If I had a small child, I would be horrified to let them anywhere near my driveway because the smell is so bad. I want to fix the smell, not just the pipes. I asked Mechanic B what he thought about getting two cats from RockAuto, but he said he wouldn't change them at all. I'm at a loss. What should I do?

A. Replace everything from the resonators back with OEM parts.

B. Replace everything from the resonators back with OEM parts and the rear O2 sensors.

C. Buy an aftermarket exhaust kit like this, O2 sensors and cats from RockAuto, and find a guy willing to assemble it.

D. Sell the vehicle.

Here's a diagram of the exhaust system if it helps:

[Mike W.]

No no no, you've got it all wrong. Your cats look more like this.



More seriously I think there's a disconnect between you and the mechanics. They're focused, perhaps by past jobs, about the odor getting in the cabin. Replacing what are perhaps damaged and leaking exhaust system parts are a likely cure to that. You are concerned about the actual exhaust odor no matter where it's at.

This is a bit of a grey area because cold starts, for emissions testing when new, is at 68F, or not cold at all. They're probably also looking at it with a view on possibly passing smog, which they interpret as meaning the system is operating as well as could be expected, which often these days means no OBDII light on. But it's not like it once was? There's basic tune up like spark plugs, more in depth like O2 sensors, the front ones, which are a b***** to replace, but not a whole lot more unless there is some sort of an air pump that runs during cold starts, which I'm not aware of, but that's not saying much. Rear O2 sensors are a complete red herring, they are monitoring only and have no role at all in emissions, they just tell you if there might be a problem. Which leaves the cats, no matter what they look like. A high quality cat will last almost forever under good conditions. Good ones last 4-8 years. Cheap ones a year or two. But even cheap new cats test crazy clean and good or very good ones do that longer.

All of which is a long way of saying if the check engine light is off, change the plugs and O2 sensors, the front ones. If that doesn't so it you're looking at cats but if you're planning on keeping it buy OE or the stupid expensive California legal ones, they should last longer. Not that cheap ones won't fix it. Just not for long.

[yeldogt]

It's not uncommon to get some odor on a car of this vintage -- the question: is the odor you are getting normal and the only reason you are smelling it is because you have a leaking exhaust system?

The R50's exhaust system is a weak point. It leaks ...The twin resonators under the front seats .. split at the seams. Nissan had a service action to fix these ....actually not a fix. They applied some mastic and twin clamps to each of them .. did not hold up. The real fix for these is to remove them from the car -- weld the seams and put them back. They are SS .. and will last forever if fixed in this way. If the mastic has been applied -- they need to be replaced .. no fix possible.

The rest of the system eventually rusts out -- would be surprised if any of them can still have the original system .. if so it's leaking.

I have had three R50's and all developed the split front resonators. The first one was fixed by Nissan using the mastic ... so when they failed again I had to replace. The pipe around the rear axel at the joint is normally the first to go .... I had a local shop weld mine together (they all want to replace - naturally!) .. my third one leaked at another joint and I had that fixed also. It's the pipes and connections that fail -- the second resonator and muffler are typically long lived. As I said .. the muffler shops what to replace the whole thing.

As to replacement: found rockauto to be my best bet for these -- I have ordered the Bosal replacements .. the front resonators in the aftermarket are simply larger tubes w/ the O2 fitting. The back two sections just bolt on. I liked the Bosal setup because the middle part is one welded section .. the walker is three as in picture.

On the one I still have the rear section was damaged by a curb -- so I had to order a replacement and only walker was available at teh time. It bolted right onto the Bosal center. I actually liked the Walker rear a bit more.

The OE system is crazy expensive -- aftermarket cheap. You will not get the service life out of the replacements -- but if the rear rust out in 4 years ... it's $120 bucks.

If you are having any O2 sensor codes -- now is the time to replace the rears. Find and get the OE number and get the OEM replacement ... don't use a universal. The wires are long and a pain to replace w/o a lift.

I got the parts and my independent installed -- it's an hour job. All the heat shields that have not rusted aways have to go as well. There is no way reasonable way to replace.

[rgk]

Thanks for this yeldogt, very informative.