Put to the Test

Maintenance Q & A — October 2002
Maintenance Q & A — October 2002
By Capt. Ken Kreisler

Put to the Test
Bench-testing a solenoid, fixing a misfiring engine, checking for voltage drop, and more.
 More of this Feature
• Part 1: Starter Solenoid, Misfire
• Part 2: Masking Tape, Epoxy, and More

 Related Resources
• Maintenance Q&A Index

How do I bench-test the starter solenoid on my 75-hp two-stroke outboard? M.L., via e-mail
Bench-testing a starter solenoid is a relatively simple procedure, and while solenoid styles vary from engine to engine, all solenoids have two large terminal studs and two small terminal studs.

Begin by disconnecting the negative battery cable from the battery. Next remove all leads from the solenoid terminal studs. There is no need to remove the solenoid from the engine. Connect an ohmmeter--calibrated on the Rx1 scale--to the two large terminal studs (1 and 2 above, in both illustrations). The ohmmeter should indicate no continuity, due to the fact that no power is running through it. Replace the solenoid if any other reading is noted.

Using jumper cables, attach a 12-volt battery to the two small solenoid studs (3 and 4, above)--polarity is not important. You should hear a click as (or if) the solenoid engages, and the ohmmeter should indicate continuity. This is because the solenoid is a high-amperage switch that when energized shows a closed circuit. Replace the solenoid if any other reading is noted.

When you are finished, replace all the leads and connect the negative battery cable last.

I'm having a steady misfire on my gasoline stern drive. What can I do to find the problem? P.A., via e-mail
Start the engine, and let it idle. Remove one spark plug wire at a time. If the misfire worsens, that cylinder is operating correctly. Continue until the misfire remains the same, indicating that cylinder is not operating correctly. Check the condition of the spark plug and its gap, and examine the spark plug wires for open cracks in the insulation. Also check your distributor cap.

I think I've got a voltage drop in the circuit that takes care of my entertainment system. How do I test if this is the case? C.H., via e-mail
If you think one of your components is experiencing a voltage drop, it is most likely due to unwanted resistance in the circuit connections, switches, or wiring. You can do a simple voltage-drop test to find the problem. Here's how.

Since the circuit must be operating, turn on your entertainment system. Next, set your multimeter to D.C. volts. As the component being tested must be between the meter's two probes, place one of the probes on one side of the component and the other probe on the other side. If your meter reads zero volts, the voltage drop does not exist at that component. Repeat this procedure for every component on that particular circuit. A voltage drop will be indicated when the meter reads voltage. Usually, depending on load, a voltage drop greater than 0.5 volts indicates a problem.

As for the culprit, long runs of undersized wiring can cause excessive voltage drops, so check your wiring runs and, if necessary, increase the wiring size. In addition, as heat is generated with voltage drops, you may want to check your components for excessive heat. Once you've isolated the culprit, have it cleaned, repaired, or replaced.

Next page > Masking Tape, Epoxy, and more > Page 1, 2

This article originally appeared in the October 2002 issue of Power & Motoryacht magazine.

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