BMW M50

I have here M50 BMW 2.5l , with MS3pro trying to get the engine started but so far no luck just back fire in exhaust pipe . Set timing with timing light 12 deg . Tested coils and injectors , calibrate temp sensors . It's modify engine with CAT 290 cams and 12:1 compression. The MS3pro should be plug and play but not much luck so far. However it will run with original BMW ECU , it will not idle but run @ 2000 RPM .

Michal,

Depending on the sound and aggressiveness of the noise, a few things come to mind. Too much fuel/not enough air sounds more gurgly, too little fuel/too much air sounds like not a lot happening or more crackly, but when someone says "backfire" sometimes that means something else entirely.

When the timing light shows on time, but the engine makes a sound someone calls a "backfire", which implies it's a bit violent sounding during an attempted start, one possible cause is firing the coils 360 crank degrees off time. If that is what turns out to be happening, altering the crank reference offset by 360 degrees will get the spark on the correct engine stroke. You'd want to again confirm the timing light shows on time after making the adjustment, then attempt startup again. I don't run into this often, but since you mentioned it runs on the stock ECU, and because you said "backfire", this may be your issue.

If you crank for a few seconds and the engine doesn't start, I don't suggest doing that over and over as it can cause the engine to load up with fuel, and then ignite enough all at once to cause potential harm.

Please let us know what you find.