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Old 03-24-2017, 12:12 PM   #1
froggydogg
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Default 1996 SL2 questions

Greetings everyone, I had a couple questions specific to the 1996 SL2, and this seemed like the perfect place to ask them.

Back in 2004, a young woman went missing from the scene of a minor accident she'd had, and she was driving this particular make/model at the time. I'm just trying to clarify a couple of technical points concerning the vehicl, and hope someone might be able to provide me with a definitive answer or two.

Did the 1996 SL2 have any sort of fuel cut-off in the event of an accident? I know it did NOT have an inertia switch, and I also know that it did have a fuel cut-off tied to security system, but I believe that is only part of the anti-theft system, and would NOT cut the fuel in an accident.

Did the 1996 SL2 have any sort of emergency fuel cut-off?

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Old 03-24-2017, 12:41 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: 1996 SL2 questions

All Saturns have a pseudo fuel cut off; the fuel pump stops whenever the engine stops running. When ignition is turned on, the fuel pump is commanded on for two seconds if the engine isn't started, then shuts off. When starting or running, the fuel pump/ignition system/injectors are alive; the crank position sensor only outputs during engine rotation. Crank sensor outputs precise timing signals to allow the PCM/EFI system to operate. No engine running, no fuel pump/no spark/no injector pulses. If a car crashes and the engine stops running, the fuel pump stops immediately. If the engine continues to run after a crash, the entire EFI system still runs; crank sensor outputs timing signals to the PCM, the pcm operates fuel pump, ignition and injectors.

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Old 03-24-2017, 01:04 PM   #3
froggydogg
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Default Re: 1996 SL2 questions

Thank you very much for your response.

Just to make sure I'm understanding this correctly: the only way the fuel would be cut-off, in this circumstance, is if the engine stopped running? If the engine was still running the fuel would not cut-off?

The car had no "impact sensing" fuel cut-off of any sort?

Thanks again for the help!

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Old 03-24-2017, 02:16 PM   #4
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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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Old 03-24-2017, 02:55 PM   #5
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Default Re: 1996 SL2 questions

Quote:
Originally Posted by fdryer View Post

Any impact sensor to disable fuel pump operation isn't needed or necessary. Impact sensors are used in another area, airbags.
I am not a mechanic by any stretch, which is probably painfully obvious by now, but this is the main reason that brought me here.

The airbags inside her car had been deployed, and a few people were speculating that as soon as the airbags go off there is a safety fuel cut-off, in which the car can't be restarted, but I've never found mention of this in my research on Saturns, and know that some other makes/models could be started regardless of airbag deployment. I know for a fact that the '96 SL2 did not have an inertia switch, so I'm just trying to rule out the "airbag fuel cut-off" as well as any "impact-sensitive" fuel cut-off.

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Old 03-24-2017, 03:20 PM   #6
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Default Re: 1996 SL2 questions

I gotta ask, and I don't mean to be cruel:

Did the entire car and driver go missing after this accident; neither has been found?

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Old 03-24-2017, 03:36 PM   #7
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1999 SC1
Default Re: 1996 SL2 questions

I was in an accident in a 1999 sl1 and the airbags deployed. As far as i remember, the car cut off when the accident happened, but was able to be restarted.
And out of curiosity, why do you need to ask about this?

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