Exhaust Popping on Overrun

[harrog8]

I've just had a new ECU fitted and mapped on the rolling road, I get lots of popping from the exhaust on overrun which sounds great, but what if any are the downsides.

[Tony C]

Blow the stuffing out yer silencer

[John Howe]

If your ECU is programmable, then you should be able to adjust it to kill the spark on the overrun - which will stop the banging.

 

JH

Deliveries by Saffron, the yellow 222bhp Sausage delivery machine

[Peter Carmichael]

Worth pointing out that a "rolling road session" might leave significant portions of the map "unmapped". There is so much attention to detail in progression from idle and high speed, WOT running that the part throttle and overrun positions can be completely overlooked.

[SLR No.77]

According to Dave Walker's book, popping on the over-run is often caused by a weak mixture at the high rev / low load sites.

Increase the fuelling at zero load site across the rev range from around 2500 rpm upwards. Should do the trick , it certainly sorted mine.

 

Stu.

[Sam Monoogian]

Going slightly off-topic but along the lines of what Peter was on about, one of my team-mates from Formula Student last year proudly proclaimed he'd mapped the engine on the dyno. When it came to testing the car would not respond well at all to any significant prods of the loud pedal, being hesitant and then spitting and banging before clearing its throat and going like sh*t off a shovel. The engine had only been mapped for steady state conditions and wasn't very good at transient responses.

 

He's now employed at Cosworth 😬

[SLR No.77]

Harrog8 - and the result is 🤔

[Paul Richards]

Don't overlook the fact that popping exhaust can be caused by a defect gasket(s) on exhaust manifold.

May not be related to ECU fitting.

 

Paul Richards

Joint AO - L.A.D.S. (Lancashire and District Sevens)

Growing old is compulsory - Growing up is optional

[dave1968]

does it do it on a completely closed throttle ? my car is 'silent' on a closed throttle but pops like buggery if on a trailing one......

 

Edited by - Dave68 on 15 Jul 2004 17:10:58

[SLR No.77]

At a completely closed throttle, chances are the fuel cut-out has come into play (depending upon the ecu). If popping is experienced at slight throttle openings on the over-run, ie. low load sites, then usually the fuelling needs increasing a little at those sites.

 

Stu.