Quote:
Originally Posted by Jammer
Hey Christ, I'm far from being a mechanic so I need to ask what may sound like a dumb question. Do you know if I am driving in EOC downhill in my Cobalt XFE that by gearing down wont waste gas? See in my warped mind I keep thinking that when that engine starts turning over, yet can not start due to the ignition key being "OFF" that somehow the motor is pumping gas into cylinders with no spark. That is the only reason I have not drove that way YET. I can not shake this idea that even with the key off if I put my car, say in 4th gear to keep me within the posted speed limit that gas is still being introduced to the pistons, and it's just the lack of spark in the plugs that keeps the engine turned off. Can you help me more fully understand how this really works? (Or anyone else that can help)
Thanks.
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Think of your injectors as a NC switch (normally closed). When you turn the key on, the ECU individually grounds them based on signals from the CPS (crankshaft position sensor)
As long as you're running key off, you won't have the problem. If you have to coast with key-on, it might be a different story.
Normally, there is a single power circuit to the injectors that gets split in the harness to go to all of them. If you can find it, put a switch on it, and use it for your engine cut off.
Spark can keep happening without damaging anything, but you don't want raw fuel flowing through your engine.
EDIT: If you switch the reference wire to the CPS, problem solved. NOTHING in the FI system works without the permission of the CPS.
The problem with either of those is that you might end up with a CEL from what the PCM will read as a "dead sensor". (The injectors, though they aren't, are randomly referred to as output sensors. They're technically actuators.)
EDIT TO THE EDIT: OF course, I'd think about the simple thing right after the edit... In the ignition circuit, you can find the single wire that is the turn on lead for the ECU/Fuel Pump main relay. If you put a switch in it, you can leave the key on, but switch off the ECU/Fuel Pump, which would still act as an engine kill switch. This may alter your odometer readings, though.
LETTER TO THE EDITOR: Umm... I think I'm done editing now.