“What I Learned Today” With Jeff Smith — Engine Hard Starts

This was an interesting exercise in applying the proper equipment to a simple slow crank problem. A close friend owned a very nice ’68 Camaro with a pump gas small-block and a Muncie four-speed and over the course of a couple of weeks had purchased a new starter motor, new battery, and finally new battery cables in search of improved engine cranking performance. However, the engine still suffered from hard starts — slow cranking speed when the engine was cold, and with the engine up to temperature, it often refused to start. Needless to say, my friend was unhappy.

He asked me if I had any recommendations beyond buying a different, high-performance starter motor. He demonstrated how the now-warm engine would barely turn over. I grabbed the negative and positive battery cables and noticed that especially the negative cable was very warm to the touch. This simple hands-on test indicated that the negative cable was experiencing high resistance, which is what created the heat.

A quick way to do a loaded resistance test on a battery cable is to connect a digital voltmeter to both ends of the cable and monitor the voltage displayed while cranking the starter motor, preferably with the ignition disabled. The voltage should read 0.5 volt or less. If the voltage is higher than 0.5 volt, this is an indication of excessive resistance. This is a reading from an LS engine swap with a permanent magnet starter and good cables and is only 123 milli-volts, which is a very low 0.12-volt.

My friend responded that the cable was brand new, just purchased from a local chain auto parts store, and therefore could not be the cause of his hard starts. So next we performed a simple voltage drop test where I placed one end of my digital voltmeter on the negative post on the battery and the other probe on the ground point on the engine. While cranking the engine to produce current flow, we read the highest reading on the voltmeter that indicated 1.1 volts. A typical reading on a good cable with low internal resistance would usually be 0.50-volts or less.

This high reading indicated that there was excessive resistance in the cable. My friend didn’t believe it so we proceeded to build two new battery cables using 00-gauge multi-strand welding cable with new copper battery cable ends that were crimped into place. With both the positive and negative cables installed, he cranked the engine over and it responded now almost like the car was equipped with a 24-volt system. Even fully warmed up, the engine now cranked over effortlessly and the problem was solved. We didn’t take the time to re-install his old starter motor but likely it would also have also performed well. In this case, a simple voltage drop test highlighted this problem and cost nothing to discover the real culprit. The proof was in the performance.

The best battery cable is multi-strand copper 00-gauge welding cable. Use a proper crimping tool like this Moroso tool from Summit Racing to create a solid connection between the copper terminal and the cable.

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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