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Coil is not getting a signal. 700 1989

posted by  otherdalek on  Thu Jan 4 08:41 CST 2007
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last visit: Sat Jul 6 18:14 CST 2013
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I am helping a friend get his car (89 740 LH2.4+T) alive. Problem is that the coil's primary is not being fed through its primary connectors. So I went with the Volvo green ignition manual and did some look-see. Here is what I found:

1. Once ignition is on, coil positive does get battery voltage. However, once the engine is cranked, its voltage fluctuates between 1.3V and 0. For reference, my car (LH2.4 turbo) fluctuates between 9V and 0.
2. Coil resistance at the primary winding is 1.6 Ohm. Book states it should be between 0.6 and 1.0 Ohm.
3. So, we went to the power stage connector. Resistance between pins 2 (its ground wire) and battery ground was 0.7 Ohm. Book expects it to be 0 Ohm.
4. When ignition is turned on, battery voltage is seen on pin 4 of the power stage connector. When engine is cranked it drops to 10-10.5V.
5. So, we measure the voltage at pin 5 (pulse signal from the ICU?) while engine is being cranked. Book expects it to oscillate between 0 and 2V. His car oscillates between 1.7V and 0.


So, are the values I got good enough? If so, why is the coil not getting a pulse from the power stage with enough amplitude to create a pulse?






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