I have the MSD 6AL set up to work with adjustable pills to varry the 2 step RPM. The setup was working fine until the engine was pulled for a rebuild with the same specs, injectors were increased from 42 to 60s, and hot parts ceramic coated. The tune was adjusted and part throttle and wot look great, but now the car is backfiring on the 2 step??????? The only thing I can gather is something is up with the fuel when on the 2 step rev limit, but it had worked beautifully before and now backfiring???
Anyone have had this happen???

Thanks for any feedback!

 

A little more information might help...Backfiring through the exhaust? Are you drag racing the car and using the 2-step at the starting line for building boost/launch control? If not, when are you activating the 2-step? Did you change timing tables when the tune was adjusted? The MSD box drops ignition spark randomly to cylinders when the rev control is activated, so some raw fuel is going through the motor, which is most likely why it is backfiring. The question is why now and not before the changes you made?

 

It is backfiring through the exhaust. It’s an M6 so using it to build boost off the line, and have just been testing it sitting in neutral. A switch is set up to activate the clutch pedal switch, and when its not activated then the msd runs off the revlimiter pill. When it is activated it runs off a the clutch petal fully depressed. I had been using it before and it would build about 6psi at about 3500-4000 rpms and would launch on boost. Timing wasn’t changed nor any of the ignition components. I understand how it drops every other spark on each cylinder which again worked fine before. I do have dual intake walbros where the 2nd kicks on with boost but this set up was on before. It seems to backfire the worst at the lower rpms (3500) and not as much higher rpms (4500). I am heading to the track this evening so I will play around with the fuel some more before going.
Thanks BoostedZ28

 

In all honesty, that is how most 2 step cars sound when it is working right.

 

i bet it is normal backfiring out the exhaust but maybe the bigger injectors richened up the mixture enough to notice it more?