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At a minimum, check the battery connections Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 31 Oct 2008 13:13:06
In Reply to: Sounds like a common problem, anyone have any luck?, JEMSaab  [Profile/Gallery]
, Fri, 31 Oct 2008 05:42:34
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A simple visual inspection of the battery clamps and posts won't do. The current flows between the post and the inside diameter of the clamp - where you can't see it. So in this case, I'd pull the clamps off (negative off first, on last), and polish up the battery posts and the inside of the clamps with some sandpaper. Peek into the ends of the cables where the insulation stops - do the wires look good, or do you see a whitish or greenish powder between the strands? If you see the powder, that is corrosion, and consider replacing the cables.
The positive cable then goes to the starter and alternator. Try to peek down and see how that connection looks.
Gee, why doesn't the alternator handle this? The A/C compressor kicking in, or any other large motor load (fans, etc.) create a very high electrical current demand, but only for a few thousandths of a second. The alternator has minimal reserve capability; the voltage regulator can't react that fast, and even if it did, the alternator can only source so much current. So for these very short, occasional loads, the current comes from the battery, which has lots of capacity.
But if the connection to the battery is poor, when that current surge comes, there is a large voltage drop across the resistance of the poor connection. Not much current flow. So the alternator must struggle with the current surge, and the system voltage drops for a few milliseconds. The EDU won't see that - you won't see it without an oscilloscope. But the fuel injection stumbles, the injectors stop injecting, etc.
The purpose of the battery is to provide current to start the car, and to provide a reserve current 'buffer' for those intermittent, large current demands. But all it takes is a poor connection, and it can't source the current. The problem may lie in the fuse box, where the current is distributed. That's a little harder to track down. But start with the battery cables.
This is nothing special with Saabs. All cars with electrical systems (which is all cars) have electrical problems. Saabs are easy - own an old British roadster, or most any Fiat. The majority of car issues, any car, are electrical. That's because all those wires, all those connections, and the lousy environment under hood of vibration and heat.
posted by 75.25.4...
, Fri, 31 Oct 2008 05:42:34, Fri, 31 Oct 2008 13:13:06 <-- Viewing This Message
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