Originally posted by: eleison
Originally posted by: Raduque
If the fuel pump shuts off at time of impact, your engine (unless the cut-off circuit fails) isn't going to be running anymore, regardless of the transmission.
edit: fixed broken quote tag
1)
If the fuel pump shuts off; if you get into an accident,
why would your fuel pump shut off? Remember sometimes airbags don't go off when they have to. Also, driving an automatic, you can go from 60-0 (basically to stop) using your brakes very quickly, but your engine still "turns" at the end. In a manual, your engine stops if you go from 60 to stop.
2) getting into an accident, wouldn't that
likely damage your "cut-off" circuits causing them to fail?
By "turns" I'm assuming you mean the engine's still idling.
The fuel pump cutoff circuit is usually a simple mechanical switch that reacts to a hard impact. I can't tell you where the relay would be located, but I can tell you it wouldn't be in the engine bay or near the most common points of impact (front end, rear end). It's very probably in or near the reset breaker which would be in the most protected section of the vehicle - the passenger cabin. Power is also routed through this system anyway, so if it fails for some reason (lets say an impact knocks it loose and a wire disconnects) the fuel pump is going to shut off regardless. It's designed to, work or fail, stop power to the fuel pump. Unless the impact is not enough to trigger the cutoff, or the vehicle simply doesn't have one, the engine isn't going to be running in a severe impact.
Judging by the damage in the picture of your linked article, I'd have to be very surprised if that engine was still running after impact, simply from damage to the engine itself, regardless of the fuel pump shutoff safety.
Airbags may not fire in a crash because those are fairly complex, computer-controlled circuity. Maybe the ECU took a knock, or even the fusebox in the engine bay came loose and disconnected from power?
If anybody knows how these systems truly work (I'm going off what I've learned by working on cars of various years), feel free to correct me.
edit: yes, I know i contradicted myself. What i meant by "fails" in my first posting was more along the lines of "fusing into a solid conductive lump".