I've noticed if I use the LH side of the J gate to engage 2 or 3 going downhill I get a periodic exhaust 'fluff' - just a discernible change in the note - in the 2-3000 rpm range. Obviously foot off throttle.
Is this normal or am I doing in the cat converters?

 

Steve,

I'll offer up two possible theories:

1. with foot off the throttle under normal 'no load' conditions when stationary or on the flat, the ECU is mapped to give the correct fuel/air mixture. Under engine braking when going downhill, the 'no load' state is reduced - it takes less energy for the engine to rotate because the weight of the car is effectively helping to turn it. The standard mixture for 'no throttle' opening calculated by the ECU therefore becomes rich and what you are hearing is this slight excess burning in the exhaust instead of the combustion chamber.

Alternatively, and my preferred explanation:

2. it's the car's way of telling you not to be such a wimp and get back on the throttle!

Graham

 

Graham,
Your first explanation sounds right, will it screw up the cats?
The second is also right - but you try following

down a series of hairpins !!!

 

Steve,

Dumping unburned fuel into the cats is never a good idea but this was probably minimal and flashing as soon as it hit the hot exhaust manifold.

Amazed you had to slow down behind the Ford. By all accounts they had virtually no brakes! It looks superb. One of the cars on the recent rally you were on?

Graham

 

The one on the rally was identical but Best Ford Black and I didn't get a photo of it by itself.
I did see an unconscionable amount of its ar*e though !

 

Perhaps not the best angle!

Graham

 

Steve-

If what you heard could be described as muffled popping or puffing in the exhaust, that's perfectly normal and will not do any harm to the engine or catalytic perverters.

 

Thanks, that's exactly what I heard. I shall remain unperverted.