popping on deceleration?

anarchyx34 · Post by **anarchyx34** » Thu Mar 30, 2006 10:35 pm

I'm posting this in the general forum because I'm not sure if it's a fuel or ignition problem. Mods please move it to where you feel it belongs.

Anyway. I'm experiencing popping from the exhaust on deceleration/engine braking. I do notice that my AFR guage drops to full lean when I let off the gas, so I cant see it being unburnt fuel, and I've toyed with the over-run fuel cut and it didnt make a difference. What could be causing this?

Toady · Post by **Toady** » Fri Mar 31, 2006 12:40 am

holes in the front part of the exhaust and small amounts of unburnt fuel... probably a combination of the two.

anarchyx34 · Post by **anarchyx34** » Fri Mar 31, 2006 8:26 am

Actually I did suspect the exhaust at first since I was running and open downpipe. But now I'm running a complete exhaust, cat converter and everything with no leaks. It probably is unburnt fuel, but how do I eliminate it?

Poweredquest · Post by **Poweredquest** » Fri Mar 31, 2006 9:16 am

I take you have heard rigs jake brake (engine braking)?
If so, then that is effectively what you are doing.
Every manual that people do it with, do it. There is no getting around it.

It is not neccesarily unburned fuel, but the high RPM engine operation with absolute minimal fuel.

Under hard acceleration and then sudden let off can cause unburned fuel popping (which with an open exhaust) usually produce a fireball out the tail pipe. RX's with a good exhaust system are famous for it.

snillet · Post by **snillet** » Fri Mar 31, 2006 10:47 am

Old carbed cars can do that frantically...
I had a Mini once with a freightened 1400cc engine and the exhaust going straight back from the header into a 2.5 inch full flow "damper".

At night you could almost think there was lightning behind the car when you revved it and changed gear

, i think itÂ´s quite cool really

kanenas · Post by **kanenas** » Fri Mar 31, 2006 12:07 pm

leaking injectors can also feed extra fuel into the system. have you run datalogs?

anarchyx34 · Post by **anarchyx34** » Fri Mar 31, 2006 3:31 pm

I havent run datalogs yet. This isnt happening from hard acceleration. I can be cruising at light load and just let off the gas and it does it.

zguy36 · Post by **zguy36** » Sat Apr 01, 2006 1:31 pm

Add some fuel during the decel andI bet your poping goes away. This is just how an engine sounds at high rpm with very lean mixtures

2WHEELENGR · Post by **2WHEELENGR** » Thu May 04, 2006 10:48 am

I think zguy36 is right. Set the decel amount higher in the Acceleration Wizard.

Karl_Skewes · Post by **Karl_Skewes** » Thu May 04, 2006 2:48 pm

we used to find this before we overrun was available in the extra code.
basically the bottom row on the VE table was 0, but injector opening times or whatever caused some fuel to go in and it would pop consistently.

as said above, adding a bit of fuel to that bottom row and it went away... it was pretty cool though (combined with some AE could make consistent flames)