Situation No. 1
You wanted to move your combine into the heated shop so you could service it over the winter. When you went to start the engine, the battery was dead. Thinking not too much of it, you jumped it, and the engine fired right up. The voltmeter on the dashboard showed normal, just under 15 volts. A week later, when you went to work on it, the battery was dead again. The next time you were in town, you purchased a new replacement battery at the dealership and put it in, figuring the battery must have just been too old. A week later, the new battery was dead. You asked some friends what you should do, and this is the advice they provided:
A. Farmer A said there must be a draw on the battery, and you need to install a disconnect on the ground cable.
B. Farmer B warned the alternator is not really charging and the gauge on the dashboard is wrong when it reads near 15 volts.
C. Farmer C told you that the voltage regulator is defective and is overcharging and ruined the new battery.
D. Farmer D says you need to check for a draw on the battery by placing either a test light or amp meter in series with the negative battery cable.
Situation No. 2
You are really frustrated and disappointed. The head gasket job on your pickup truck with a gasoline engine you paid $2,000 for failed after 800 miles. The shop that repaired it in town says the gasket must be defective and all they will do for you is get a new gasket; you will have to pay the labor again. You decide to fix it yourself since you do not use the truck every day. You are concerned your repair may also fail, so you talk to others after church to see how you can avoid this. They are anxious to give you their advice:
A. Farmer A says you need to check the flatness of the head and block deck, study the failed gasket for an imprint, have the head resurfaced to the proper RMS (even if it is not warped) and use new head bolts, and all will be good.
B. Farmer B thinks the thermostat is bad, and you cooked the engine.
C. Farmer C tells you to see if you can get a cast-iron head to replace the aluminum one.
D. Farmer D is firm in believing that once a head gasket fails, the engine is junk and will keep doing the same thing.
Situation No. 3
Your wife’s SUV put on the “service engine soon” light. She has noticed the fuel mileage has decreased, and when she is stopped at a traffic light in town, the exhaust smells like rotten eggs. You take the car to one of the chain auto parts stores that offer a free computer scan, and they tell you it has a code for “lean mixture.” You ask the person checking it how it can be lean when the exhaust stinks and the fuel economy is very poor. He shrugs his shoulders and tells you, “That is what the computer says.” You are now confused, so you install a new oxygen sensor, and the problem is gone. How can the engine be both lean and rich? Your buddies at the coffee shop offer this explanation:
A. Farmer A believes the computer was telling half the injectors to go lean and the other half rich, and the problem is not fixed.
B. Farmer B says the catalytic converter is tricking the code reader, and the engine has some other problem.
C. Farmer C told you the engine computer is bad and confused about what to do.
D. Farmer D says the original oxygen sensor failed, and that was the problem.
Answers
Situation No. 1: Farmer D is correct. If the battery on any piece of equipment is dead while not in use, there is a draw on it. That means something is staying powered up when it should not.
The only accurate way to confirm this is by disconnecting the battery ground cable and putting a digital amp meter in series between the battery negative terminal and the ground cable connection.
If the meter reads amperage, then go around unplugging circuits or fuses until it reads zero. Then, the circuit that eliminates the draw is the problem.
A test light can also be used. If it illuminates, there is a draw. A test light can be misleading with newer equipment since the energy used to keep computer memory alive will illuminate it. However, on older machinery, this test is OK. That is why it is best to use a digital meter.
If you cannot find the draw, disconnect the field circuit (small wires) from the alternator. A weak diode can back feed to ground and still allow the alternator to charge, albeit at a lower rate.
Situation No. 2: Farmer A is correct. When a head gasket fails, you need to figure out why. Once that is established, the surfaces need to be checked for any warpage, new head bolts must be employed, and the finish on the cylinder head needs to meet the requirements of the gasket maker.
The surface finish is measured with a profilometer and is maybe read as RMS for “root mean square.”
Skip any of these steps, and the repair may not last.
Situation No. 3: Farmer D is correct. An oxygen sensor reads the oxygen content of the exhaust in reference to the atmosphere. An internal chemical reaction creates a minute voltage that is correlated to an air/fuel ratio.
As the sensor is exposed to the exhaust, it becomes coated, and its output voltage skews lower. The engine control system interprets this as a lean mixture and adds fuel to satisfy the oxygen sensor.
Most systems can influence the mixture strength around 25%, rich or lean. Once that control value is eclipsed, the mixture is considered out of control, and the warning light comes on, and a code is set.
Thus, the mixture is truly rich, but the skewed sensor is saying it is lean.
