Sudden electrical failure of charging and interior shortl after starting engine

HALODADSON

MEMBER
2003 HYUNDAI ELANTRA
2.0L
4 CYL
2WD
AUTOMATIC
160 MILES

Since 6 months ago the engine would not start and then suddenly start ok. Recently I changed the battery and then the alternator because abruptly the car looses electrical power. The tach drops to 0 the a/c fan starts blowing slowly because the car is running off the battery and the engine eventually dies also. Then I boost start it and the tach pops up to normal rpms and the fan blows hard as normal for about 3 minutes then the tach drops to 0 and the a/c and power shut off and the car idles for a couple of minutes and then dies out. There is an abrupt loss of electrical power after the car runs for about 3 minutes. I just watch the tach and can see when the disconnect occurs then the engine dies out. I have wasted money on a new battery and alternator. There are no codes on the code reader. I have new battery terminals also. I have swapped the starter relay with another relay but no help. I have ohmed out all fuses and they are good. Yesterday I drove the car for about 15 minutes before the tach dropped and the a/c fan slowed and I managed to get home with it running bad. This morning it will only run for about 3 minutes before the electrical failure but can be started with a boost and the electrical will be back up for about 3 minutes or so then cuts off. It seems as if something is going open which controls the alternator power to the car but this is the second alternator I tested it with the meter and it puts out good voltage. And why does it boost start right away with good voltage and then only last a few minutes before a power disconnect. Can some circuit be opening because of the power or heat? It`s almost like there is a timer on the electrical circuits for it to cut off after a few minutes.

Image (Click to make bigger)

1 Reply

CARADIODOC

MECHANIC
33,910 POSTS

There's two things to look at. First, follow the smaller battery positive wire to the under-hood fuse box and be sure that connection is clean and tight. Follow the smaller battery negative wire to the body and be sure that one is tight and not rusty.

Second, when you can get the problem to act up, use an inexpensive digital voltmeter to measure the battery voltage with the engine running, then measure the voltage between the generator's output stud and a paint-free point on the engine block. Those two voltages must be the same all the time. If you find the second one is significantly higher than battery voltage, there is a break in the wire going from the generator to the battery. There's usually a fuse in the circuit, and since it's so large electrically, it is almost always bolted into the fuse box. Fuses are never intermittent, but the connections can be. Be sure those nuts for that fuse are clean and tight.