Rotten Egg Smell

[Murman25]

I have a 1976 911 Carrera 3.0. After the car warms up for about 20-30 minutes, a rotten egg smell fills the car. Does anyone have any ideas what might be causing this? I have great digestive health, so I know it's not me

[Tippy]

Possibly your voltage regulator is cooking your battery by overcharging.

[Steve@Rennsport]

Another possibility if your car has a cat would be a horrible rich fuel mixture and an overheated catalytic converter.

[motofoto]

I experienced this with my voltage regulator going south as well.

[S4hounddog]

I experience the exact same thing in my 1984 Carrera 3.2, but not all the time. At first, I thought it was a dead rodent stuck somewhere under the 911 but nothing was found.
The smell only occurs after being parked outdoors and on a slight hill. It happens immediately after start up and only lasts a few minutes. It never occurs when I'm parked in the garage. I've installed a CAT by-pass but the smell still occurs, so it's not the catalytic converter. I suspect it's condensate that collects after exhaust system cool down. The condensate may be reacting with some of the fuel's residual by-product ( small amounts of sulphur?). Just my theory of course.....sometimes I just open the windows.
If the smell fills your car after 20 or 30 minutes of running as you describe, I'd check for exhaust leaks entering the cabin, you may have a leak after your CAT.

[Bill Douglas]

Originally Posted by Tippy

is cooking your battery

My thoughts too.

I'd check the battery as an easy first step.

[timmy2]

Check the voltage at the battery when the car is running and post your result.
Do it in a well ventilated area and try not to create any sparks.!!!'

[sky1jord]

+1 on Voltage Regulator.
With the engine running, the voltage at the battery needs to be watched for a couple of minutes and at various RPM's, as a failed/failing regulator may cause surging between normal and abnormal charging levels. As I recall 14 Volts @ 2500 rpm is normal charging voltage.

[wwest]

Amazingly enough a FAILED alternator can boil the battery electrolyte..!

Shorted or open a stator segment, the VR "pumps up" the output in order to have the average voltage output be in the correct range.

The VR does not "see" the (remote, "filtered") battery voltage, only the high ripple content alternator output.

CDI often fails due to the "local" over-voltage.

[JV911SYDNEY]

Originally Posted by Tippy

Possibly your voltage regulator is cooking your battery by overcharging.

+1

Been there, done that

Although it would probably only happen once and the next time you went to start your car the battery would be dead

Originally Posted by S4hounddog

I've installed a CAT by-pass but the smell still occurs,

aren't you more likely to get a smell with no cat?

[strikee]

Voltage regulator cooking battery BTDT.

[JJ 911SC]

Originally Posted by strikee

Voltage regulator cooking battery BTDT.

Me too and you don't want to breath that for too long.

Cheap way to monitor you battery short of having a permanent voltmeter instal.

Amazon.com: INNOVA 3721 Battery and Charging System Monitor: Automotive

[S4hounddog]

Originally Posted by JV911SYDNEY

+1

Been there, done that

Although it would probably only happen once and the next time you went to start your car the battery would be dead





aren't you more likely to get a smell with no cat?

Nope, the CAT delete odour is very different. As mentioned, it's happend with and without the CAT, it's a rotten smell that lasts only a few minutes......still haven't found any dead rodents???
The other possibility may be that I bought the 911 with a bad CAT and the odour is same with or without?