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I have a question about a bad block ground that only occurs under load, specifically while cranking. In conducting tests, I've found it's standard practice to perform a voltage drop test. In this test, you connect a lead from the battery's negative terminal to the engine block, then load the circuit or crank the engine to reveal a fault. I've done this successfully, but I have a question: Why would there still be a bad block ground if I've supplied a good pathway to ground? Could it be that the test lead wire can't handle the load, or is the resistance greater due to the smaller AWG of the lead? If I removed the block ground and just left the test lead connected from the battery negative to the block, would the vehicle crank, short the wire, or not even attempt to crank because the wire is insufficient? Lastly, if I had a spare 2 AWG wire, could I technically run a temporary path from the battery negative to the block and crank the vehicle to prove a bad ground theory, even with the bad block ground still connected? Or would it need to be disconnected? I have other questions but I feel this is my main disconnect. Any insight to articles to review is appreciated.

Please repost this. We were having forum issues that seem to be fixed now. The font is this is completely unreadable. Thanks!

Mobilemechanics wrote: I've found it's standard practice to perform a voltage drop test. In this test, you connect a lead from the battery's negative terminal to the engine block, then load the circuit or crank the engine to reveal a fault.

To be clear, you are using a Volt meter to do this test. The Negative test-lead of the volt meter goes to the negative battery post. The Positive lead of the volt meter goes to the engine block. Attempt to crank the engine, and read the volt meter. The closer the reading is to zero, the better. If you read a voltage reading of more than a few hundred milli-volts, there is a problem.

Why would there still be a bad block ground if I've supplied a good pathway to ground? Could it be that the test lead wire can't handle the load, or is the resistance greater due to the smaller AWG of the lead?

A test lead is not heavy enough to be used as a block ground.  Properly, using a volt meter to read engine block voltage puts 10 MΩ of resistance between the Negative battery post and the engine block.

  If I removed the block ground and just left the test lead connected from the battery negative to the block, would the vehicle crank, short the wire, or not even attempt to crank because the wire is insufficient?

It would, likely, burn/blow the test-lead like a fusible link.

Lastly, if I had a spare 2 AWG wire, could I technically run a temporary path from the battery negative to the block and crank the vehicle to prove a bad ground theory, even with the bad block ground still connected? Or would it need to be disconnected?

Yes, you could do that. You would not need to disconnect the existing cable.