Originally Posted by Airborn44
Well I am back already...I figured Ill take the generator apart and meassure the rectifier. Said and done it all looks normal to me, all diods only letting current through in one direction and all values equal between all diods.
After I put the generator back together and on the car to test run it, the voltage without the B+ cable attached (only field current cable attached) was 13-14 volts. I then attached the B+ cable, again sparks and a drop in idle rpm. I now meassured the current at the b+ terminal as well as directly over the battery terminals and voltage was jumping between 14 and 16.7 volts!!!!
I dont think its the alternator anymore....if it is regulated by the PCM then thats where the problem should be?
I will remove the PCM now but it is located quite wierd.
My question now is if I throw in another PCM will I need to reprogram anything or should it just work assuming its no other issue creating the problem. I will also replace the alternator as I have already ordered it.
Greatful for any tips regarding replacement of the PCM.
Cheers for now!
Those voltages with the alternator being controlled by the PCM are not good.
Anything over 14.5 to 14.7 volts tends to result in highly reduced battery life [and can void a battery warranty at places where they test your charging ckt before replacing] and anything over 15 can be bad news not only for the battery but for the electronics, and 16.7 is just bad bad news as you could generate enough hydrogen in the battery to make it explode.
I wouldn't be connecting and disconnecting live on a modern vehicle, you could get a voltage spike enough to fry stuff. And never ever disconnect the battery if the alternator is driving any of the electronics. Peak voltages in the 100 range or better can last for a few hundred milliseconds, and a lot of magic smoke can be released.
I don't suppose you have a battery with a warranty from someone like Sears, where you could get a free test?
I tend to agree, sounds like your PCM may be toast, but it could still be something in the cheaper alternator... the PCM will typically just crank up the field current in order to reach the charging voltage of at least 13.8 and then try to keep it under about 14.5 by dropping the field current.
Depending on the response time of your meter, you could have a wierd battery problem, in that the battery acts to damp out the pulsating DC that an alternator and diodes produces. Not as likely as the voltage regulator in the PCM dropping too much current into the field windings [if you have a clamp on current probe, can check that as well] and causing excessive voltage.