Hey guys, i get alot of popping/backfiring on deccel more at 3.5k or so. I use and wide band and tunnercat i have read alittle about messing with deccel fuel cut off constent, but im not sure the right way to go about solving the backingfiring. The car use to have a 80's flowmaster cat back which did it like crazy....... put on sweet thunder true duals and it got better but it still some time about 4-3k it will backfire so bad it will shoot flames out of the pipe. Not kool reminders me of vin deisle....Let me know if there is a trick to the fuel cut off or a good place to learn about the solving the problem.

 

U have an exhaust leak somewhere and your fuel cutoff is not working.

Basically your fuel cutoff should kick in anytime over 2000rpm while off the throttle but anytime you have a backire on decel is because you have air mixing in the hhhhot exhaust/fuel combination.. so really it takes both to ignite fuel.. if you had sealed exhaust you would not have a backfire no matter what AFR you had UNLESS you re-ignite the spark then one BIG BANG would occur but only if you had the right mixutre in the pipe...

 

I might have a exhaust leak but i know that my fuel cut off is working because i see it on my wideband. i see anything over 1800 there is about a 1 sec delay then it goes 22.2 afr. i would think this is correct because thats what my constents are set at 1 sec delay and 1800 rpm and higher.i have a snap on smoke mechine at work i will see if i can find the leak with that .....

 

Fuel cutoff can only be confirmed from the datalogs... if PW says 0 then you have 0 fuel (AKA Fuel Cutoff). AFR should increase through 22AFR all the way to 20.9% 02.

1 second delay is about right but still you should have more than 22AFR.
Best thing to do is run it at idle and put hand over pipes and listen for leaks.. somewhere they will show up.

Unless you have 4" pipes or Air Injection you should have no backfire. Check EGR, Air Tubes, something like that... even leaky gaskets will do it.

 

my inj PW on deccel is 1.60~ are u saying that it needs to be 0?

 

PW should be 0 when it's in Decel fuel cutoff mode... if injectors are opening then your not in decel fuel cutoff mode (DFCO)

Not always when you decel your in decel fuel cutoff mode, only sometimes.

usually if your driving around 40-50mph and your above 1800-2000rpm when you let off gas you should enter decel fuel cutoff...

 

lt1street, the PW=0 window is short, coming off acceleration at 4500 RPM my injector PW goes to 0 for 1.2 seconds until my MAP recovers and gets back above 27 kpa (constant setting). However my Delay Timer is set at 0.0 SEC for an A4, my trace shows about 1.2 sec after TPS=0 my MAP is back up to 27 kps and PW=2.75. If I had a 1.0 sec delay my DFCO window and PW=0 would only be for 200 MS . In reality DFCO is a rare occurrence for me, with my cam I rarely see MAP under 23 (DFCO enable MAP).

dookie454, my stock A4 delay is 0.0 sec , but an M6 stock delay is 1.0 does the M6 need the 1.0 delay to smooth out the deceleration

 

I think stock is ok with 1sec delay but I think I moved mine to 0 delay so I avoid the decel transition from slight power to full decel cutoff.. Imagin letting off the gas feeling the decel rate then 1second later feeling an increase in decel rate... to me it was annoying so I changed it so there's only one decel rate which is full decel.. no switching from partial to full.

With the cam and my injectors getting the transition from DFCU in and out was a little harsh.. this way is the smoothest I got it and now I dont really notice it.