Backfire on overrun

[Rossjude1983]

Hi guys,

so my 172 that’s new to me backfires like crazy on overrun as it drops below about 2800 rpm.
It’s on a decat with itb conversion.
Pulls fine, I suspected a exhaust leak so went through the whole system to no joy.
Any ideas or is this just a thing with itbs?

 

[Brigsy]

Might have some fuel or timing pulled on decel if no exhaust leaks. What ecu is it on?

 

[Rossjude1983]

Ktec gen90

 

[Brigsy]

Prob wants a map tweak to tame it a bit. Who mapped it?

 

[Rossjude1983]

Just noticed I have a very slight misfire on high rpm now…. Brilliant

 

[green]

I’ve had the hi comp bottom and ITB’s for 8 years.
When I had standard cams in my itb hi comp engine it was fine but since I’ve had high lift Schrick cams put in and mapped I’ve had to increase the butterfly’s opening so the engine wouldn’t stall once warm.
Since screwing in the idle screw to increase the revs it pops and bangs on over run all the time not super loud but I can hear it..quite like it
Tick over revs are 1100rpm
I would get the ITB’s serviced and map checked if I wasn’t saving for a wedding
What sort of tick over do you have when warm?

 

[Rossjude1983]

I’m not sure if mine has had cams, idles well when warm around 900 rpm, not to horrible when cold either….. I may try winding it down a little to see

 

[kurai]

Hello, my car has same ITB kit, same Ecu, a 63,5 exhaust with cat and does same. When dropping rpms under 2800it begins to pop and bang a lot and continuously.. like turbo cars with antilag.
I too am looking for exhaust leaks because I feel A noise near cat that makes me think about a leak. As soon as I finish mounting the new oil cooler for next trackday I'll check and report!
Interesting the thing about butterfly openings.. I'll do a vacuum check too