Exhaust pipe colour

skyestuart

Junior Member
Messages
33
Just wondering if my engine is running a bit rich? as the exhaust pipes at the back are very dark coloured sooty looking. Back in the days when I did my own maintenance checking here was a good way of seeing that the mixture was correct and it should be a light brown colour.

Advice very welcome :)
 

Zep

Moderator
Messages
2,767
Due to catalysts cars tend to run a bit richer than you could before (a very slightly lean mixture was the norm) where as these days it has to be stochiometric as much as possible. Add to that maps that are probably erring on the rich side when pushing on in performance engines (not closed loop operation using the oxygen sensors), I wouldn’t be too concerned about a bit of soot.
 

77GR

Junior Member
Messages
43
An MoT emissions test immediately reveals any rich running, even if it's not excessively so.

If you had an MoT recently or the exhaust looked the same at the last one then you are fine, if the Mot's due soon then that'll do. If you are really worried (and as Zep suggested, you probably shouldn't be) then get a friendly MoT station to do a quick emissions test it only takes a few minutes.
 

skyestuart

Junior Member
Messages
33
Thanks Zep and 77GR I'm reassured I got the MOT done in April no issues then, I guess owning a Maserati is making me a bit hyper paranoid :)
 

Boomerang_GT

Junior Member
Messages
136
Interesting that this issue is coming up right now.
I just noticed black dust on my friends 3200 GT like form an old Diesel.
Mine are shining inside. His car is also lacking power in the upper gears.
Might be an issue.
 

alfatwo

Member
Messages
4,271
So are mine with just a hint of brown water vapour staining
But I've been told from people following in the dark there's blue like flames coming out of the exhaust on the overrun, what's all that about?

I've seen similar on Top Gear track tests!

Dave
 

CatmanV2

Member
Messages
29,504
It's unburnt fuel igniting in the hot exhaust. What makes the bangs and crackles on overrun. Well done!

C
 

FIFTY

Member
Messages
1,661
It's unburnt fuel igniting in the hot exhaust. What makes the bangs and crackles on overrun. Well done!

C
More typical for turbo cars though surely?

My 4200 bangs and pops on the overrun a lot but I doubt it's kicking out any flames
 

Ebenezer

Member
Messages
1,839
Isn't there some school of thought that, for ceramic cats at least , these bangs and crackles are to be avoided? The thinking is that the combustion is degrading the cats which might then be injested into your engine?
Eb
 

FIFTY

Member
Messages
1,661
My ceramic cats are long gone mate

But yes you don't want the stock euro spec cats on the 4200 to do that because it means they have failed/are failing or have been hollowed out already
 

alfatwo

Member
Messages
4,271
There's no bangs and pops as its a 3200 turbo. The standard ECU doesn't allow for over fueling on the overrun..
So what's all this blue flame stuff, I first saw it when Clarkson was testing a Lamborghini around Imola!

Dave
 

Zep

Moderator
Messages
2,767
Let’s keep a sense of perspective. The pops and crackles we hear on the overrun when we have x pipes etc are all still happening without them, the sound is just muffled by the resonator.

Ceramic cats break up because of physical damage or manufacturing defects, not because of some shockwaves in the exhaust.
 

CatmanV2

Member
Messages
29,504
More typical for turbo cars though surely?

My 4200 bangs and pops on the overrun a lot but I doubt it's kicking out any flames
I don't think so. I assume Zep will be along to explain in detail why I'm wrong.

Close the throttle fast on any motor and I can visualise the ECU not quite catching up so the the next (couple) of cycles are over rich, don't burn...

C
 
Reactions: Zep

Zep

Moderator
Messages
2,767
There's no bangs and pops as its a 3200 turbo. The standard ECU doesn't allow for over fueling on the overrun..
So what's all this blue flame stuff, I first saw it when Clarkson was testing a Lamborghini around Imola!

Dave
It is the unburnt fuel in the exhaust combusting in the presence of a lot of oxygen.
 

Zep

Moderator
Messages
2,767
I don't think so. I assume Zep will be along to explain in detail why I'm wrong.

Close the throttle fast on any motor and I can visualise the ECU not quite catching up so the the next (couple) of cycles are over rich, don't burn...

C
Exactly that :thumb3:

As well as the fact that some of the fuel will have coated the sides of the inlet tract and will then be drawn in under the increased vacuum behind the throttle plate.
 

MRichards

Junior Member
Messages
97
Better stop talking about the blue flames,next you know the fan boys will be pestering you to sell them packets of blue flame,oh maaaaaaaate ! Look at me !