Detonating while decelerating?

[Structure240sx]

sometimes while im decelerating i hear a loud bang like a backfire, but while looking at my wideband display it looks more like im lean than rich enough for a backfire. i thought you would only detonate while boosting. is this bad? it doesnt happen very often and i played with my decerlation air settings on my safc to keep it richer. it will still happen very often tho. can damage be down to the motor? could it really be backfiring and my eyes arent quick enough to see it on the wideband? also i did a compression check today and got 180,175,175,175, built 9:1 DE

[C-Kwik]

That's not detonation. Detonation sounds like ball bearings being flung around in your combustion chamber. What you are hearing is likely unburned fuel igniting when it hits air. You won't see detonation on a wideband. You can only see a condition that might cause a condition where detonation can likely occur(rean mixture). But even with a rich mixture, things like timing that is too far advanced, high compression, heat, and/or low octane fuel can cause detonation. When decelerating, you do not need a rich mixture. There is less load there and peak pressures will be much lower than under boost. Under cruising, and deceleration, you can run leaner mixtures. The reason you run richer mixtures under boost is to use the atomization of fuel to reduce the temperature of the air. Like water, fuel absorbs heat when it evaporates. And reducing charge temps will reduce the chance of detonation.

[Structure240sx]

thats what i thought just needed someone to make it clear. thanks

[Checkered-Member]

C-Kwikif I understood correctly he needs to lean out his mixture at cruising and deceleration?

[MikeMurphy]

I get the same problem, along with many other people. I just bought an safc2 so I would be interested in your settings once you have it figured out.

Im guessing you leaned it out on the decel and it fixed it?

[C-Kwik]

C-Kwikif I understood correctly he needs to lean out his mixture at cruising and deceleration?

If he is running as rich as he is on boost, then likely. I can't say for sure since I am going of what he is saying but it sounds that way. It would explain the backfire under deceleration.

[TopStreet240]

Man i love when that happens... I have only a downpipe and I light up the town when the fuel burns... guys on the local strip love to roll down there windows to tell me that my car is on is on fire... I just laugh and drive off!