reducing deceleration fuel

[MarkM]

I am tempted to change my fuel map to reduce fuel when off the throttle. This will lean the mixture and make the exhaust pop and bang.

Can this cause any damage ie to the cat and silencers?

What effect does it have on engine braking?

Is it a good or bad idea?

Whats a resonable amount to take off?

 

[edde]

Off throttle your engine won't be injecting any fuel apart from whats needed to idle the engine I belive so no savings.

You want to add fuel i think.

 

[Bailey_1260]

Yaeh will pop and bang when running rich as there is fuel int the exhaust.

Mates Bug does it, is funking sweet.

 

[MarkM]

Off throttle your engine won't be injecting any fuel apart from whats needed to idle the engine I belive so no savings.

You want to add fuel i think.

My only reason is to make it pop and bang. If you look at the map below you can see the deceleration fuel circled in black. This is the fuel added when off the throttle.

 

[MarkM]

Yaeh will pop and bang when running rich as there is fuel int the exhaust.

Mates Bug does it, is funking sweet.

I thought it was when the mixture was too lean and does not ignite properly in the combustion chamber which spits unburnt fuel into the hot exhaust manifold where it explodes.

 

[John D]

I thought its more likely to pop when running rich rather than lean.

 

[Jim NM]

The reason an exhaust pops is unburnt fuel in the exhaust which causes a build up of soot. When the soot heats up it explodes causing the popping (mini explosions). This means your engine is running too rich.

 

[MarkM]

I knew I had seen this on here recently.

Popping on overrun is an indication of lean running, hence it happens on overrun or trailing throttle etc.

A lean burn is slower than a stoich or richer one, hence its still burning on the way out.

 

[dannyboy172]

My scoob is running rich and sometimes during spirited driving with no trottle but down changing (engine braking) i get a nice pop, bang, warble, warble. loves it!

 

[Dan@SJM]

valvers pop and bang with decats all the time

mine pops and bangs nicely with just a straight through centre section!

 

[Waitey]

Running rich is myth.

A lean mix is slower burning. So when the exhaust valves open it is still ignited hense a pop or bang.

Mark leaning things out it a dangerous business. I'd rather be on the rich side of things than risk holed pistons etc

 

[BenR]

sadly mark, altering that particular area will not only affect overrun fueling, but also the point of acceleration fueling from nill to 10% throttle. It will not make part throttle on/off driving very nice.

Decelleration fueling is available in another table, but is only adjustable in a on/off nature within its own trigger points.

 

[ben_p]

ebay chip?

 

[MarkM]

sadly mark, altering that particular area will not only affect overrun fueling, but also the point of acceleration fueling from nill to 10% throttle. It will not make part throttle on/off driving very nice.

Decelleration fueling is available in another table, but is only adjustable in a on/off nature within its own trigger points.

I didnt think of that. So when you come back on the throttle you have to little fuel.

Thanks I wont change it then. That area does seem a bit erratic on the AFR meter. How would you map that line? Can you do it off the AFR?