2004 GMC ENVOY
90,000 MILES
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Every so often my battery goes dead . But now i realize when i use the defrost it will make car run rough and than it will die. I allready changed the alternator in it. But that didnt help....any ideal? I can use the heat in any other spot and it runs fine.
Feb 28, 2013 at 4:42 AM
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CARADIODOC
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Have your new generator load-tested. If it can only develop exactly one third of its rated output current, and "ripple" is very high, it has a defective diode. 30 amps from the common 90 amp generator is not enough to run the entire electrical system under all conditions. The ripple can result in elusive engine running problems.

If you find the generator does indeed have a bad diode, replace it again, and to reduce the number of repeat failures replace the battery at the same time unless it is less than about two years old. Due to their design, these generators produce huge voltage spikes. As the battery ages it loses its ability to dampen and absorb those spikes.
Feb 28, 2013 at 9:07 AM