Ok, occasionally when I'm driving with the windows down at around 55 mph or so, an intense ammonia smell engulfs the cabin. No, it's not a sulfur smell, I know what that smells like; this is like breathing deep a thing of Windex.
This problem only occurs when the windows are down so my guess is it's from somewhere in the engine compartment, but it is definitely not the same smell as a bad cat converter. It's almost as if someone left a Windex bottle in there and it heats up occasionally but that's not the case. At least pretty sure.
Has anyone else experienced a similar smell? And for clarification, 2003 V8. Thanks

It comes from the exhaust just like the sulfur smell. I have experienced this a few times with the rear window down and me gunning the accelerator, even worse when I am going up a steep hill. I have never experienced any smells if my rear window is up. Somehow it is a product of the combustion process and/or the attempt at "cleaning" it from the cat converter.

Sulfur, amonia are somehow byproducts of the combustion process and I'm sure you could find a very technical/chemical explanation if you searched hard enough.

Sulfur should only be present in very small amounts in gasoline, but unfortunately our noses can detect sulfur compounds in the parts per billion range. Ammonia, on the other hand is much different and its disconcerting to hear this. The engine produces oxides of nitrogen from the combustion process. Heat causes mostly inert nitrogen in the air (79% of air is nitrogen) to burn in the combustion chambers producing NOx (x could be 1,2,3). The catalyst is supposed to take NOx's and change them back to N2 and O2. Ammonia is NH3 so somehow the catalyst is taking NOx and reacting it with hydrocarbons (unburned gas), CxHy (x and y could be almost any number).
You saw my nerdy side, sorry. Have the catalyst looked at if you smell ammonia, although its less toxic than either hydrocarbons or NOx's.

So if the cat is reacting hydrocarbons with NOx to produce NH3 (ammonia) and ammonia is less toxic that NOx and hydrocarbons isn't that a good thing (relatively speaking)?

Ok, thanks. I'm taking it into the shop in a few days so I'll be sure to mention it.

I've been trying to work out the same problem on mine as well. V6 engine and same year. Replaced sensors, cleaned everything, checked vacuum and hoses, used higher octane low sulpher gas, etc etc. No resolve.

Last oil changed I noticed the rubber seal in the oil filler cap was hard and compressed and didn't seem to be sealing the crankcase. That coincided with a bit of soot build up, over time, on the inside of the tail pipe. Still had a ton of power and gas consumption wasn't too bad. I wasn't worried about piston rings or valve seat wear. Wasn't burning oil or blowing smoke.

I pick up a new oil filler cap, that had an improved rubber seal, fitted it and went for a half day drive testing the motor under load at speed and hill climbing. This sort of driving would normally bring out the ugly odours I had also cleaned the soot off the tailpipe.

At no time on that trip did I get the odour back and checking the tailpipe I found it was as clean as whistle and no soot.

I'd been analysing this smell for 60k, spent a lot of time and reasonable $$$$ trying to resolve it. For a small amount of time and money, hopefully, I've solved the dilemma for good. Over time I've found that we tend over analyse stuff like this and usually its a simple solution like this was.

Hey Flips did this prove to be a solution that held up over time? Getting an ammonia smell from my 05’ 6cyl when accelerating hard up hill.

I years ago posted the same question (for my 2009 V6 Ltd). Same situation, it only happens when engine is temporarily stressed like accelerating / going up hill. It doesn't happen frequently, and it maybe occurs once and then no repeat of the issue during the day.

No one here could answer (it's not related to sulfur). I asked at my dealer (they have the best price for synthetic oil change - never go there for serious service but I have only 80k miles and have needed none) and no one in the service department could answer, none owning T4Rs has had the issue.


So, 10 years later, with 80k miles, nothing has changed. T4R is running great, love it, but the issue does happen a couple times a month - no answer, I guess it's no issue.