How to diagnose a no

Published: July 31, 2023

Machinery and Shop

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Nearly every farm has at least one or two older pieces of equipment that still need to put in a day’s work during busy seasons, such as an auger tractor or sprayer tender truck.

In 2020, Case IH introduced the two-model line of Vestrum utility class tractors offering 100 and 130 horsepower, respectively. In…

One of the most common problems on older machines is the sound of silence after you hop in and turn the key. Nothing happens, and usually at the worst possible time.

Now the challenge is determining why. Is it a dead battery, or is the starter worn out?

Maybe it’s neither, since there are a few things that can prevent that starter from spinning over.

Of course, there are a number of ways to approach the problem without breaking out the tool box, and anyone who has farmed for a while has probably tried them all at least once or twice.

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The first and most obvious thing is to try boosting the battery with another machine. If the battery was dead, you’ll be off and running. If there’s no response, a few light taps on the starter body with a hammer might bump the armature enough to move past a dead spot and spin.

But if neither of these steps produce results, it often leaves more than a few people scratching their heads and dreading the thought of having to diagnose an electrical problem. Often the temptation is to replace the battery or starter or both.

However, by knowing how to use a multimeter and with an understanding of current flow, electrical problems on basic systems can be easily pinpointed with a few logical steps.

By taking it one step at a time, it’s easy to look at all of the potential problem areas and determine which is the cause. Testing the battery is the logical first step.

A quick and easy indicator is to turn the lights on. If they come on and shine brightly, the battery has a decent charge. Dim or no lights indicate a dead battery.

With a multimeter set to the 20-volt setting, try attaching each lead directly to the battery posts and turn on the headlights for a minute or so to get rid of any surface charge the battery might have. That will allow you to get an accurate voltage reading.

If the battery shows zero voltage, it has an internal short and is useless. A fully charged 12-volt battery should show at least 12.6 volts.

If you get a reading like that, don’t move on to testing other components yet. A sulphated battery may show good voltage when tested this way, but when put under load its voltage drops off too quickly.

Leave the multimeter attached and try starting the engine. That will put a load on the battery. It should hold a voltage level above 10 for at least 30 seconds. If it doesn’t, you may have found the problem — or at least one of them.

Remember, older machines may have several components that aren’t operating as well as they should. Often the problem comes down to a combination of things.

If the battery’s initial resting voltage was low, it isn’t fully charged. Is it no longer capable of holding a full charge, or is the alternator (or generator on really old stuff) not charging?

To find out, boost the battery and start the engine, then put the multimeter leads back on the battery posts. With the engine running, a working charging system should create a voltage reading of 13.5 or higher. The charging system needs to have a higher voltage than the battery to force a charge into it.

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If the tractor has an old-style generator, you’ll probably have to throttle the engine up above 1,000 r.p.m. or so to get it to charge. Older generator charging systems may put out little if any voltage at idle speed.

If the voltage stays low, the charging system has a fault in it somewhere.

If you’ve ruled out the battery as a problem, the next step is to see if battery voltage is making it to the starter. Since we’re already at the battery, check the battery cable connections. A visual inspection may show excess corrosion that can hamper current flow.

Remove the cables, clean off any corrosion and ensure they’re tightly reattached to the battery posts.

Check to see if the original cables may have been previously replaced with some that are too light. With a little corrosion, they may no longer be able to carry enough current to the starter. If cables feel hot after a few attempts at starting, this may be the problem.

Next, check the voltage at the starter end of the cable. It should be within a few tenths of the battery voltage. There will be some natural voltage drop along the cable, but it should be relatively small.

To determine that the cable is delivering the full battery voltage to the starter when it’s needed, the voltage at the starter has to be tested under load (during current flow), with the ignition key turned to the “Start” position.

To do this test, connect the black lead of the multimeter to the battery negative post and the red lead to the end of the cable at the “B” terminal on the starter solenoid. Then, try cranking the engine.

An accurate test can only be done when there is a load on the circuit (current flow) because a cable in poor condition could allow battery voltage to show at the starter connection when there is no current flow. But when there is a load, current flow is restricted and voltage drops. It may fall to a level that is too low to activate the starter.

If this test shows a significant reduction in voltage, the problem location can be narrowed down by connecting the multimeter in a different way. Attach the red lead to the battery positive post, and the negative lead to the end of the cable on the “B” terminal at the starter solenoid.

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With the key off, the meter reading will be zero. When the key is turned to the start position and current is flowing, the meter should only measure a few tenths of a volt. A higher reading indicates that cable and connections are restricting current flow.

The same test can be done on the negative side of the circuit by attaching the positive meter lead to the starter body (a starter grounds to the engine through its body) and the negative lead to the negative battery post. Again, there should only be a reading of a few tenths of a volt when current is flowing.

This often confuses those who don’t fully understand how current flow affects voltage. Some mechanics may even use the Ohm setting on a multimeter to check battery cables, placing one lead on each end of the cable and measuring resistance.

However, a bad cable may still show very low resistance to current flow when tested this way because the amount of current used by the multimeter is low and the cable can handle that amount, but not the high amperage required to spin a starter.

If battery voltage at the starter solenoid drops below about 9.6 volts, it probably won’t be enough to spin the starter over.

Connecting a jumper cable from the battery positive post to the starter connection will likely get the starter to spin if there is excessive voltage drop because the cable is bad. It gives electricity a path of lower resistance.

Now, imagine all of these tests check out, and everything seems fine. Next, we need to be sure the ignition key switch is sending 12 volts to the “S” post on the starter solenoid.

Again, using the multimeter, place one lead on the solenoid “S” terminal and the other on battery ground. With the key turned to the “start” position, there should be a reading close to battery voltage.

It’s also possible to use the multimeter to measure voltage drop using the method described above, connecting the red lead to the battery and the black to the “S” terminal at the starter.

Voltage from the ignition’s switch circuit at the “S” terminal activates an electromagnet inside the solenoid, which closes a switch connection and allows battery current to flow to the starter from the battery cable.

If there is no voltage showing when tested, or the voltage drop is excessive, it’s time to start looking for a fault in the ignition system wiring. There is likely another relay and neutral safety switch in this circuit, either of which could be faulty, among other possibilities.

A remote starter switch with one lead connected to battery voltage at the “B” terminal and the other to the “S” solenoid terminal will activate the starter if the ignition system is at fault. Use an 18-gauge jumper wire with a 10- or 15-amp fuse if you don’t have a remote starter switch handy.

Resist the urge to take a shortcut and touch a big screwdriver or wrench across those two terminals to activate the starter instead of a remote starter switch. This can allow too much current to flow to the solenoid and fuse the internal connection, which will then not allow the starter to disengage after the engine starts.

(Ask me how I know.)

If everything checks out and voltage readings are what they should be at all critical points but there’s still no sign of life, the starter may be at fault.

If the machine has been sitting for a long time, make sure there is no mechanical fault in the engine that prevents it from turning over. Place a wrench on the crankshaft bolt and see if the engine will turn. Ensure it’s not seized.

I have seen an occasion where rodents built a condominium inside the bell housing with so much material that it prevented the starter from engaging the flywheel. Check for problems like that when the starter is removed.

Bench testing the starter after it’s off the machine can confirm its death. Connect it to a battery and see if it turns. But be aware that without a load, a starter in poor condition might still spin over. It may not have enough torque to spin a high-compression engine.

Diagnosing a starting system failure doesn’t require a lot of high-tech tools, at least on older equipment or more basic, non-computerized systems. It’s just a matter of following a logical process and understanding how current flow problems can occur and how to detect them.

Contributor

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.

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