bad exhaust smell

My modified 83 turbo wagon has a very strong and unusual exhaust smell on decel coming out of boost. If i'm pulling in 3rd gear and let off the throttle, I get a wave of stench directly in the cabin that's so bad it stings my eyes. The car has a homemade 2.5" stainless exhaust with Ebay cat, cherry bomb resonator, and slightly angled up tip coming out under the tailgate on the passenger side. This problem started after I installed this system with a 90+ mani and 15g. Before I installed the turbo and exhaust, I had the original exhaust and cat with the midpipe cut and the tip coming out the side, right before the rear passenger wheel with no smell. If I have all the windows closed, there is hardly any smell.

At first I thought it was paint or residue on the cherry bomb baking off, but the smell hasn't gone away. It doesn't just smell like rich exhaust, its much sharper and not a smell I'm familiar with. I just replaced my cracked manifold to eliminate that as a cause, but theres no change. I've smoke checked the exhaust and it has two very small leaks at the welds rear of where the rear seats would be, nothing major. I tried putting a turn down at the tip since the pipe was slightly angled up, without much noticeable change in the smell. It's not an exhaust smell I'm familiar with, and I've only had factory catted cars, so I'm thinking maybe its because of the cheap cat, but that's doesn't explain why the smell is so strong when the tip is at the back of the car, not close to the front windows. I can see I'm rich in decel (around 10 afr or so).

The car has no a/c, and I want to take it to the track in Willow Springs where its often 100*+, so windows closed is not an option. I'm thinking that the exhaust stinks because of the cheap cat, but I'm confused as to why the smell is so strong and coming into the cabin if I have any windows open when the exhaust tip is at the back of the car. Is exhaust smell getting sucked into the cabin with any window open normal? Any suggestions on how to proceed fixing this issue?

video to show tip angle

A sharp smell makes me think of coolant, did you up the boost with the 15g? Possibly your headgasket is on its way out, should smell like anti-freeze if it is making its way towards the tip.

Exhaust smell often makes its way into the car if there is a small leak somewhere underneath or on the downpipe, letting it run and going past all your joints with your hand should allow you to find the leak. You could also plug the end, if it still runs, you have a leak.

Possibly intercooler is filled with oil and big pulls suck that into the engine?

My car had a nasty smell on tip out occasionally which i'm pretty sure was oil/blowby hc from the pcv entering the intake and filter. A Mann pro-vent in line fixed that nicely.

Does it have a cat? Un-catted cars just stink.

Swedbrick said:

A sharp smell makes me think of coolant, did you up the boost with the 15g? Possibly your headgasket is on its way out, should smell like anti-freeze if it is making its way towards the tip.

Exhaust smell often makes its way into the car if there is a small leak somewhere underneath or on the downpipe, letting it run and going past all your joints with your hand should allow you to find the leak. You could also plug the end, if it still runs, you have a leak.

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Nah, it's not a burning coolant smell, although that does smell terrible as well. This is burns your eyes more.

esmth said:

Possibly intercooler is filled with oil and big pulls suck that into the engine?

My car had a nasty smell on tip out occasionally which i'm pretty sure was oil/blowby hc from the pcv entering the intake and filter. A Mann pro-vent in line fixed that nicely.

Click to expand...

I've considered crank case fumes as a source but it seems sharper than that. Intercooler has a bit of oil but nothing crazy. I'll double check anyway.

740atl said:

Does it have a cat? Un-catted cars just stink.

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It's got a very cheap Ebay cat. I have a better magnaflow on the way. I'm hoping this is the solution.

Today I smoke tested the exhaust cold and it's got more small leaks than I found last time I tested it hot. Looks like the dp flex pipe is leaking pretty bad, as well as the waste gate pivot which is annoying, I just had it off. When my new cat comes in I'm going to take it to a fab shop down the block and have them fix all the leaks and replace the flex pipe and cat.

Since it was pretty leak free when hot, I tried plugging up every hole I could find in the body including the fresh air vent by the tailgate, the buttcheek buttholes, and any other opening left from when I removed the interior and all fasteners. I even blocked off the heater core vent just to see. Its the same deal, any window cracked and it stinks on decel. Smells 100% normal with windows closed. Hoping it's just the cheap cat/leaky exhaust and it'll be better with a magnaflow and no leaks.

The BOV was the cause of going super rich in decel. I forgot to add that when describing my setup. But for anyone in the future, k-jet does not seem to tolerate BOVs. It might with a stronger spring, not sure. Removing the vac signal fixed the problem.

I use a bypass valve because with kjet I didn't want to lose the metered air to the engine. Just be sure to aim the bypass air into the turbo so you don't get air blowing back to the air flow sensor plate. On decel you may be sucking something in like oil past the turbo seals.

If it is an acrid smell that slightly burns / stings your nose and eyes (makes them water), I expect you have just experienced the wonderful effects of NOx. Without knowing your ECU arrangement / fuel maps I am not sure why you experience it most on trailing throttle.

A 3 way catalytic converter is part of NOX control. The other major component is usually EGR although EGR typically does not operate at high engine loads - OEM ECUs on port injected engines typically suspend EGR above about 70 - 80% engine load. Assuming most of your car is 1983 vintage and sort of California spec I would expect that the original cat would have been a later design 3 way cat (as opposed to early 3 way cats that required an air pump supply to provide O2 to the cat) or the really early 2 way cats that did not do NOx control. If your Ebay cat was a simple 2 way cat you are likely not getting any NOx control. In order for a modern 3 way cat to work the narrow band O2 sensors have to be functional because they assist in driving the AFR continuously above and below 14.7 to replenish O2 on the catalyst surface. 3 way cats only do their thing if the average AFR is sticking around 14.7. Under wide open throttle its okay to go below 14.7; but, if you have fiddled the fuel maps to run continuously below 14.7 the cats NOx control will be severely impaired / non existent.

Chances are that your eye watering exhaust stanch has existed for a while. When moving, station wagons have a real low pressure zone in the tail gate area that tends to suck stuff in (discovered that when carrying some really long 2x4s in my 745 T with the 2x4s propping open the tailgate a couple of inches). If your tailgate gasket is in poor condition or you have other body leaks in the tailgate area your relocation of the tailpipe to the back of the car has probably precipitated the stench getting sucked into the car.