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Old 03-24-2017, 02:16 PM   #4
fdryer
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Join Date: Jan 2006
Location: NYC
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2003 L-Series 3.0L Sedan
Default Re: 1996 SL2 questions

Safety design in EFI systems dictates a way to ensure high fuel pressures with the pump running won't contribute to a crash by fueling a fire. GM, and most likely all vehicle manufacturers with EFI/high pressure fuel injection found a simple and elegant method to ensure pump operation ceases if the engine doesn't run. The heart of GM's EFI system is the crank sensor. The ecm/pcm cannot run without it and only run when the sensor detects engine rotation. Read the previous descriptions again to understand basic EFI system operation.

Ask yourself a simple question. If an engine runs, do you want the fuel pump running or not? EFI requires higher than older carburetor fuel system (7 psi) fuel pumps. EFI systems runs between 30-60 psi of fuel pressure for injector operation. If a fuel pump stops, how will an engine continue to run? If you don't fully understand fuel pump operation, start your car and locate the fuel pump fuse or fuel pump relay. With the engine idling remove either the fuel pump fuse or pump relay. Observe how long the engine runs. As fuel injectors continues to operate, the loss of pump operation means loss of fuel pressure until the engine dies from lack of fuel pump operation. The crank sensor still outputs but this experiment is to see how long the engine runs without power to the fuel pump. Technically, if you are able to disconnect one of two wires to the crank sensor or able to disconnect it altogether, this effectively duplicates an engine stopping, if an engine stops in a crash, to kill EFI system operation (no pump operation). In a horrific crash where a fuel line is ruptured, the sudden loss of fuel pressure will result in lower pressures to injectors. Lower pressures with a leaking fuel line usually means the injectors cannot spray enough fuel per injection cycle so the engine starves, stumbles and eventually stops. The leaking fuel line will pump out fuel but only when the engine remains running. No one can predict how long a leaking fuel line/engine running will continue but if enough pressure is lost, the engine will starve itself of fuel (loss of pressure to injectors) until it stops. This might be a worse case scenario with possibly a fuel fire. If you were to examine the crash history of vehicles with EFI systems, you might find that the majority of horrendous crashes never results in a fire unless the fuel tank ruptured and an ignition source ignited spilled fuel.

Any impact sensor to disable fuel pump operation isn't needed or necessary. Impact sensors are used in another area, airbags.

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