What would make the exhaust smell. I don't even know how to describe it. It's not like the rotten egg smell some Cats produce. It smells even if there is no cat and a straight pipe.

It has always smelled since I have owned it and is nothing new.

Have some time and thought I would try and track it down.

I was thinking carb, but it runs and idles great.

It does not smoke out the exhaust. Although the car is white with a white bumper and sometimes
will have a yelowish stain i scrub iff from time to time.

any ideas

 

does it smell like unburnt fuel maybe its an aquired smell

 

Pat, that's normal, rotaries have a certain aroma. You use this to get your tuning right.

This is normal:

"Although the car is white with a white bumper and sometimes
will have a yelowish stain i scrub iff from time to time"

Got pics?

 

It's the smell of the burning tears of Prius drivers.

 

I'm thinking maybe un-burnt fuel ?
Although I would think it would run rough if that were the case?

If it were un-burnt fuel would that be the float bowls sticking ?

 

Rotaries run rich. The extra unburnt fuel, along with the air pump helps the cat system do it's work. Yellowish stain is a new one on me. What brands of fuel, coolant and oil do you use?

 

Thanks for the replies,
I use typically Shell or Mobil super 91 or higher. Prestone antifreeze and Castrol GTX oil.

 

i wouldnt use premium on a n/a pointless unless youve done porting

 

Most likely this is the cause!

Actually it sounds normal, as all of mine have had an off exhaust smell.

 

To minimize the emissions be sure the car is well tuned. You might want to check the idle mixture to be sure it's set right.

Isopropyl alcohol and a soft cloth does a great job of removing that yellow tarnish over the tail pipe from lighter colored cars.

I had my biggest problems with the yellow tail pipe syndrome when I was premixing gas by adding some MMO to the tank, in addition to the normal OMP. When I quit doing that most of the yellow over the tail pipe went away.

 

Thanks for the replies. I will try 87 Octane on my next fill up. It has new plugs and air filter.

I have played with the idle mixture but did not seem to make a difference regarding the smell.
I have the air pump installed and I think it's working but to be honest I have not check that air is actually comming out the pipe into the Cat.

One thing I know that is not right is several years ago I plugged the big vacum hose due to a honking noise at idle, I think this is a bad Shutter Valve?
The car seems to run fine with this plugged but I realy don't know if this is causing any of this smell.

Its running so well I hate to to anything drastic.

 

i dont mean to thread jack... but do you really need to run premium unleaded in a ported engine? i have been running regular on my street port for a while. i dont think its detonating, at least i dont think it has. what does detonation sound like?

 

I dont think you need premium on a ported engine, Octane requirements are a result of compression, porting the engine does not increase compression. I have a street port, been running regular in it for fourteen years with no problems.

 

You won't need to run anything higher than 87 on any NA, porting or not.

Mazda back in the IMSA days ran 82!

 

Do you or don't you have the cats? My impression was you didn't. If you still have them, then yours might be past their useful life.

Honking = shutter valve.

We could run lower than 87 octane, if it was available.

 

If you were premixing while still using omp I would think your stain would more likely be from the burning oil rather than a rich a/f mixture imo.in most cases i see Stained bumpers on our cars from all the poping and flames because of the rich mixtures but also from cars with bad oil control seals or that burn to much oil but you can clearly smell the differenc from runing rich and burning oil

I actualy enjoy the smell of exhaust fumes our cars give off just make you think Race car while getting you high dnt take to much tho... And dnt worry you wnt die till after the burning sensation in your eyes go away

Look at most 90-00 hondas with vtec(usualy loud enuff/Ricey to notice) if white and not cleaned constanly should have a disgustingly black rear bumper from always driving in Vtec(Burns Lots of Oil about as much as Bp spilled) you can even
see black puffs of smoke when they shift

 

Yes, it was the oil making the stain on my white car, not the gas or idle mixture. It went away when I stopped adding the extra MMO to the tank.

It's not something you might think about if you are premixing, but it fits with Pat's symptoms (foul smell, yellow stain over the pipe) so Pat you might want to take a good look at your oil delivery, both intentional (OMP and/or premix) and unintentional (oil control rings, etc).

The "extra" oil might not show a lot of obvious smoke at the exhaust but still be enough to cause the smell and stains.

 

Thanks very much for all the help with this.
Originally the car several years ago, had the stock Cats and stunk of this same odor. I then went to mind train headers with a single free flow cat from them as well and a racing beat muffler. This was also several years ago. The car sounded better after that but I still noticed the smell. Again the smell is anoying but something I have lived with but would like to resolve if I could.

I have a replacement pipe I also had put in last year. I didn't notice any difference in performance or smell, so I put the cat back into place.

So I get this smell regardlaesss if the cat is there or not.

"Bad oil control seals" Sorry I probalby should know this, but what / where are these.
sounds like this would be internal to the engine ??

 

I'll let someone who knows the engine better explain the oil control rings, but the idea is that your engine is burning more oil than it needs to.

If you still are using your original Oil Metering Pump (OMP) you might want to check the OMP output - this is a good thing to do every year or so just to be sure it is putting out enough oil. In your case, it might be putting out too much. It is easy to check and adjust, see the FSM for the methods.

If you are premixing your oil buy adding two cycle oil or MMO (Magical Mystery Oil) be sure the ratio is right, you might just be using more oil than you need (like I was).

Most likely though is that your engine is 25 years old and leaking a bit of oil here and there into the combustion chambers, like most old rotaries do. My 85 GSL does this, even though the engine runs great and has good compression and power. Not a big deal, I just need to check on the oil and add some a little more often than I did with my previous 12As. And I figure it might be a bonus (other than the smell and stain) because a little extra oil in the combustion chamber helps with lubrication of my 125,000 mile apex seals.

On a totally different note, it is strange that the cat doesn't have an effect on the odor, usually a functioning cat will reduce the exhaust smell noticeably. So maybe it's not the exhaust but some other source, most likely something cooking under the hood.

Possibilities are an O ring leak that is spilling oil on the outside of the engine - when the oil heats up it might be giving the odor. Another would be a leak in your intake manifold coolant seals, which might slowly drip coolant onto the hot exhaust - this would most likely produce a sweet steamy smell. Do you ever need to add coolant? Or brake fluid? Small leaks in these systems could be adding to the smell.

 

Thanks Ray.

Now that I think of it, When I purchased car many years ago, the metering pump linkage was off and the pump was frozen. I oiled it up and put the linkage back on.

Maybe I need to look at it a little closer. Maybe it's not on correct and allowing too much oil or maybe the pump is allowing too much oil.

I have looked down the carb and see oil dripping in at an idle? maybe too much?

Maybe not fuel problem at all.

Thanks

 

if you let gas sit for a while, it will rotten and that smell results from it