A good place to start is by measuring the battery voltage, first, with everything turned off, then while a helper cranks the engine. With everything off, a good, fully-charged battery will measure 12.6 volts. If it is around 11.0 volts or less, the battery has a bad cell and must be replaced.
During cranking, the battery voltage must not drop below 9.6 volts. Commonly you'll find around 10.5 to 11.0 volts. If the voltage remains high enough, we need to go further to see if the starter is drawing excessive current or if there is insufficient current flow due a poor connection. This test is complicated by the fact the engine will start running too quickly. One way to prevent that is to leave the ignition switch off, and use the starter relay under the hood to activate the starter.
GM has had two common problems starting with the 1987 models when they redesigned their starters and generators. We may need to do some tests on the charging system if nothing else shows up.
Let me know what you find with those voltage tests. If you need help using a digital voltmeter, I can help with that too.
Sunday, March 16th, 2025 AT 12:24 PM
