strong exhaust smell
#1
07-23-2019, 08:52 AM
strong exhaust smell
Last Friday my 2008 MCS started smelling strongly of engine exhaust. I usually don't smell it if all the windows are closed, but if the windows or sunroof are open I often get a good whiff as I'm taking off from a stop and occasionally when driving around at slower speeds in town, and by the time I get home from work my wife can smell it on my clothes. The odd thing is the smell reminds me of an old car from before cats, or a motorcycle - not a modern car exhaust smell.
I bought the car with 99k miles in March of '19, and it's had a P0420 catalyst efficiency code every time I've run codes and comes back shortly after being reset. I had decided not to mess with it because I've already spent enough doing walnut blast, thermostat housing and crossover pipe, and vacuum pump replacement, and oddly, the code can be present but not illuminate the CEL when there aren't any other codes active. But now, with the smell, I'm wondering if the cat has continued to get worse and finally crossed a threshold.
I reset the codes yesterday morning and have driven about 150 miles in 3 start/stop cycles since then, and the code hasn't returned yet. I also looked at live data and saw that the catalyst temp ran around 712°C while I cruised down the highway at 83mph. Readings from O2 sensor 2 don't look wildly wrong, and the short term and long term fuel trim values all look reasonable, though I don't really know what to watch for.
Please help...with as much as I've had to do with this car in only 4 months of ownership I'm seriously considering selling it and buying something boring for my commute, which is a sad thought given how excited I was about buying it. Losing the ability to drive with the windows down, or possibly spending several hundred more on cats without knowing for sure that's the problem may be the last straw.
I bought the car with 99k miles in March of '19, and it's had a P0420 catalyst efficiency code every time I've run codes and comes back shortly after being reset. I had decided not to mess with it because I've already spent enough doing walnut blast, thermostat housing and crossover pipe, and vacuum pump replacement, and oddly, the code can be present but not illuminate the CEL when there aren't any other codes active. But now, with the smell, I'm wondering if the cat has continued to get worse and finally crossed a threshold.
I reset the codes yesterday morning and have driven about 150 miles in 3 start/stop cycles since then, and the code hasn't returned yet. I also looked at live data and saw that the catalyst temp ran around 712°C while I cruised down the highway at 83mph. Readings from O2 sensor 2 don't look wildly wrong, and the short term and long term fuel trim values all look reasonable, though I don't really know what to watch for.
Please help...with as much as I've had to do with this car in only 4 months of ownership I'm seriously considering selling it and buying something boring for my commute, which is a sad thought given how excited I was about buying it. Losing the ability to drive with the windows down, or possibly spending several hundred more on cats without knowing for sure that's the problem may be the last straw.
#2
07-28-2019, 11:28 AM
3rd Gear
do you have an after market exhaust?
when i put a catless downpipe on and cut out the midmuffler i was getting a BAD exhaust smell even after the douwnpipe had burnt in.
turned out to be an exhasut leak i couldnt really hear but was there, coming from the downpipe connection to the exhaust.
if you are getting CAT codes you need to replace it dude. or the upper and lower O2 sensors. if you remove the downpipe you might just find out the guts of it are all lose inside. but chances are its clogged.
i got this for the lower even though i could have left he bung plug in it since mario tunes out the lower o2.
might work for the upper too.
might as well grab this too
if the cat isnt doing its job there is an insane difference in the smell of your exhaust from CAT to no CAT.. smells like your engine is dumping fuel down the exhaust.
but if you get a rotten egg/sulfer smell that can be a CAT too a clogged CAT can do that, or a coil, but if it smells like that you would know if it was a Coil pack.. the car would literally only be firing on 3 cylinders.
when i put a catless downpipe on and cut out the midmuffler i was getting a BAD exhaust smell even after the douwnpipe had burnt in.
turned out to be an exhasut leak i couldnt really hear but was there, coming from the downpipe connection to the exhaust.
if you are getting CAT codes you need to replace it dude. or the upper and lower O2 sensors. if you remove the downpipe you might just find out the guts of it are all lose inside. but chances are its clogged.
i got this for the lower even though i could have left he bung plug in it since mario tunes out the lower o2.
might work for the upper too.
might as well grab this too
if the cat isnt doing its job there is an insane difference in the smell of your exhaust from CAT to no CAT.. smells like your engine is dumping fuel down the exhaust.
but if you get a rotten egg/sulfer smell that can be a CAT too a clogged CAT can do that, or a coil, but if it smells like that you would know if it was a Coil pack.. the car would literally only be firing on 3 cylinders.
#3
07-29-2019, 10:03 PM
do you have an after market exhaust?
when i put a catless downpipe on and cut out the midmuffler i was getting a BAD exhaust smell even after the douwnpipe had burnt in.
turned out to be an exhasut leak i couldnt really hear but was there, coming from the downpipe connection to the exhaust.
when i put a catless downpipe on and cut out the midmuffler i was getting a BAD exhaust smell even after the douwnpipe had burnt in.
turned out to be an exhasut leak i couldnt really hear but was there, coming from the downpipe connection to the exhaust.
I did however, find that the flex connector between the first and second converters has corroded to the point that the ribbed outer sleeve is completely separated at the downstream end (so I can grab it and compress it toward the front of the vehicle) and has visible cracking around the upstream end. I started looking down there after I opened the hood and was greeted with the odor, which makes sense why I smell it strongest after taking off after a light - I'm filling the engine compartment with exhaust and then it comes out and into any opening it can once I start moving.
I can't feel or hear any leaking there, but if it's leaking through the segmented inner portion of the flex connector and out around from inside the ribbed sleeve, I can imagine it being slow enough to not generate any noise or be perceptible by hand. I'm taking it in to a muffler shop tomorrow morning to get the flex connector replaced.
if you are getting CAT codes you need to replace it dude. or the upper and lower O2 sensors. if you remove the downpipe you might just find out the guts of it are all lose inside. but chances are its clogged.
i got this for the lower even though i could have left he bung plug in it since mario tunes out the lower o2.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
might work for the upper too.
might as well grab this too https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
if the cat isnt doing its job there is an insane difference in the smell of your exhaust from CAT to no CAT.. smells like your engine is dumping fuel down the exhaust.
but if you get a rotten egg/sulfer smell that can be a CAT too a clogged CAT can do that, or a coil, but if it smells like that you would know if it was a Coil pack.. the car would literally only be firing on 3 cylinders.
i got this for the lower even though i could have left he bung plug in it since mario tunes out the lower o2.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
might work for the upper too.
might as well grab this too https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
if the cat isnt doing its job there is an insane difference in the smell of your exhaust from CAT to no CAT.. smells like your engine is dumping fuel down the exhaust.
but if you get a rotten egg/sulfer smell that can be a CAT too a clogged CAT can do that, or a coil, but if it smells like that you would know if it was a Coil pack.. the car would literally only be firing on 3 cylinders.
I'm not one to throw parts at a problem so I' intend to do exactly zero before I can nail the code down to either a bad catalyst or a bad sensor. I lean toward catalyst today because of the smell, but I haven't been able to find enough info about what the O2 sensors should be to condemn them OR the converter. Either way I've got it all saved and ready to order once I figure it out.
#4
07-31-2019, 10:04 AM
so I got the flex connector replaced yesterday and things are better, but I do occasionally still get the odor if the windows are open and I take off from a light after sitting idle for a bit. I can also smell exhaust from the turbo/cat area under the hood when the engine is running. So it seems the flex pipe wasn't the only leak, and I guess buying a new cat/downpipe will probably fix the leak AND the code. Can't pinpoint it without taking off the heat shielding. I don't like a disassembly project without my backup vehicle, so it'll probably be a couple of weeks before I get to it. Of course this would happen while I have the axles out of my Jeep to install new gears and locking diff.
#5
07-31-2019, 04:43 PM
so I got the flex connector replaced yesterday and things are better, but I do occasionally still get the odor if the windows are open and I take off from a light after sitting idle for a bit. I can also smell exhaust from the turbo/cat area under the hood when the engine is running. So it seems the flex pipe wasn't the only leak, and I guess buying a new cat/downpipe will probably fix the leak AND the code. Can't pinpoint it without taking off the heat shielding. I don't like a disassembly project without my backup vehicle, so it'll probably be a couple of weeks before I get to it. Of course this would happen while I have the axles out of my Jeep to install new gears and locking diff.
In my car's case the problem was a loose brick that sometimes got out of position. I finally got tired of the knocking when cold and the buzzing when hot and I bought 2 exhaust manifolds/converters from a salvage business and had them installed. Ah peace and quiet again and no more P0430.
In the case of your car I suspect there is an exhaust leak ahead of the converter or the converter has developed a leak. Be sure all exhaust pipe joints if any use a "gasket" or some kind of a seal (my Porsche Turbo used metal o-rings one per side to seal the turbo to the exhaust and these o-rings were not reusable) the seal/o-ring/gasket is present and in good condition.
You'll also have to carefully inspect the converter. The converter can have a heat shield around it and you will probably have to remove the converter to get the shield off and thus be able to look for any leak. A small leak might be weldable. You will have to run it by a highly regarded car exhaust shop which may or not not want to touch the converter due to emissions laws/regulations.
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