Backfire in exhaust-too rich or lean when cold?

[E34-520iSE]

I left work tonight (10pm) got in my car, started it up, drove for 1/4 mile or so until I got on a fast road, then put my foot down a fair bit. The car took off like it usually does and then I heard a quiet 'POP' sound and saw a puff of smoke (and probably a flame) in the rear view mirror. Obviously I felt the misfire too. My question is this - 'what's going on?' Is it a mixture problem or a heavy right foot vs. cold engine issue? The outside temp was around 2 deg. C.

Thanks for any replies,

Shaun

[SnakeyesTx]

This is a tough question here... There's so many possibilities.

Try this. If its still cold out. Let the motor warm up to the halfway mark, and re-create the travel as closely as possible and see if you get the same result.
If so, then obviously the fault doesn't lie there.

Since fuel injector pulses and timing are the issues regulated by the crank position sensor and cam sensor, now would be a good time to make sure those are okay. Stomp test if you have to for codes, or test the sensors with a multimeter. Since you mentioned the backfire was coming out of the tailpipe and not up the intake, you're clearly firing late, not having pre-detonation. My guess is a spark issue. Since the crank/cam sensors act similarly to a pickup coil, I'll put my theory into the fault lying there.

[632 Regal]

backfires rule of thumb (at least for normally aspirated engines)

through the intake=fuel
exhaust=electrical

[E34-520iSE]

I know for certain that the engine would never have backfired if it was warmed up. Could the backfire be caused by the engine being cold (ie rich) and driving with the WOT switch open? Is the Motronic unit able to compensate for this event? I am not looking to 'fix' something that isn't broken, but I'd like to understand exactly what is happening here.

Thanks for your replies guys!

Shaun