Question about 1994 Pontiac Grand Am
My 94 grand am (3.1L) will start but dies when the key goes to the running position. replaced the computer, ignition switch, crank sensor. keep getting a knock sensor (ESC) code but tested the sensor and it checks out o.k. in the process of checking the wires but about almost all the wires are good. have a diagram for the wiring out of the Haynes book, but no diagram for the wiring from the ignition into the car. any ideas would help alot
I'm not sure your car even has one but the symptom is reeeaal familiar; 'starts fine, dies afterward.'
Ignition coils used a special resistor or a relay that switched one in or out of circuit depending on whether you were starting the engine or afterward, running it. The special resistor started at a low value of resistance but rose rapidly to a higher one allowing more current to flow through the coil primary to start. The design using a relay simply bypassed a fixed resistor (not heat sensitive) during the cranking of the engine.
The resistor allowed either a full 12 volts or at least a good bit of it to be used for starting by supplying the primary of the coil with a much higher voltage than needed to only keep it running. This allowed the use of a 'hotter' coil that stepped up the voltage more than was done 50 years go. That high current could not be tolerated for longer periods as it would eventually cause heating to the point of coil failure.
If you can come up with an electrical diagram of your ignition system, check the path of voltage to the ignition coil and keep an eye open for a symbol of a zig-zag line inside of a rectangle, a symbol often used in other schematics, and if you have one that has an arrow across the zig-zags, this is the thermally sensitive resistor that needs no relay to function.
These were often mounted on the fire wall, not far from the steering column so the wire run wasn't overly long and are often in a ceramic rectangle with wires attached to either end.
Posted on Sep 28, 2008
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