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Old 07-24-2010, 08:39 AM
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Test IC Module circuit

Your truck has tan with black wire for timing adjust as you stated. during start up when the engine is being cranked there is no voltage present on this wire and the module grounds the circuit timing stays at base ( O degrees) after the engine starts the and PCM sees around 400 rpm ( during upstart) it supplies a 5 volt signal to this little tan with black wire. This causes the ignition module to switch to computed timing effectiveley switching from base timing. Here is what you do... backprobe the tan/blk wire with a DVOM of good quality at least 1 megohm internal resistance hook the red lead to the cicuit and the other to a suitable ground. Turn key on note the reading should be zero or real close then start the truck and watch to see if it changes to 5 volts, if it does not your pcm is defective if it does the module is defective.If you scan it you may see a code 42. this is the code for that circuit. It will set when you unplug the connector and remain for a certain amount of key cycles. clear it out and see if it reappears under normal conditions.this manuever along with the DVOM reading should tell you what you need to know
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