Situation No. 1

Your 1990 GMC pickup with a 350 and throttle-body injection is running rough and stalling. It has always been a good truck and never acted this way before. You check for vacuum leaks and can’t find any. It runs as if it is lean. A propane enrichment test through the valve cover breather with the positive crankcase ventilation (PCV) disconnected proves there is not an internal leak. Stumped, you ask some of your friends.

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A: Farmer A says that the engine is sucking air past the valve guides, and that is the problem.

B: Farmer B suggests you check the exhaust gas recirculation (EGR) valve first, to see if it is being sent a vacuum signal at idle and (if not) if the pintle is carboned-up and not sealing.

C: Farmer C thinks the fuel pressure regulator has failed.

D: Farmer D feels the top ring on the pistons is worn.


Situation No. 2

You rebuilt the engine on your JD 4020. Now with about 40 hours on it, coolant is leaking out of the weep holes on the block. You installed all new O-rings. Thinking the worst and frustrated, you look for advice.

A: Farmer A tells you to calm down and take the cylinder head back off and check to see if the O-rings did not seat properly or got nicked or torn during assembly.

B: Farmer B feels the block is cracked, and you did not notice it.

C: Farmer C says the head gasket is on backward, and that is why it is leaking.

D: Farmer D believes that the head bolts are too long and are bottoming out.

Situation No. 3

You are working on your center pivot and find that there is an issue with one of the microswitches. You look in the manual, and it says the switch is normally open. You are not familiar with that term, so you ask around.

A: Farmer A tells you that means during regular operation the switch is open, or not passing electricity.

B: Farmer B says Farmer A has it backward – a normally open switch always passes electricity.

C: Farmer C says they are both wrong, the switch stays open when the circuit is not powered up.

D: Farmer D says the manual has a misprint, a switch is either on or off.

Situation No. 4

The guys at the coffee shop are talking about how multiple batteries are connected. Some are connected positive to positive, and others positive to negative. You do not understand why this is.

A: Farmer A says when wired from positive to negative, that is a series circuit. Positive to positive is a parallel circuit.

B: Farmer B tells you it is the exact opposite of what Farmer A said. Positive to negative is parallel and positive to positive is series.

C: Farmer C tells you it is done to double the amperage to the starter.

D: Farmer D says it makes no difference; they do that to use the shortest cables.


Situation No. 1: Farmer B is correct. The most likely cause is either an EGR valve that is being evoked by a faulty vacuum control circuit or is not sealing due to carbon under the pintle. Exhaust gas is inert (does not burn) and is leaning the mixture. Since a propane enrichment test into the valve covers showed no improvement in idle quality, Farmer A is wrong – it is not the valve guides. If the propane test was not performed, then Farmer A has a valid suggestion.

Situation No. 2: Farmer A is providing the most practical advice. Since it took around 40 hours for the leak to begin, the most likely cause is an injured O-ring. In this instance, the cylinder head needs to come off, and everything studied in detail.

Situation No. 3: Farmer A knows his circuits. A switch can either be normally open or normally closed. When open, no electricity passes through it, and when closed, it does. A normally open switch is usually (but not in all instances) in a control circuit. The term “normally’ refers to the status of the switch under intended use. For example, a lawn tractor can use a normally open or normally closed switch under the driver’s seat, depending on how it is wired. If it is connected to the voltage supply to the coil, then it would be closed when you sit down and open when you get up. If it is grounding the coil, then it would be open when sat down and closed when you get off the tractor.

Situation No. 4: Farmer A is correct. In a series circuit, the voltage of the multiple batteries is added together, but the amperage potential stays the same. With parallel wiring, the voltage stays the same, but the amperage is added together. When you jump-start a car, you go positive to positive, negative to negative. This is a parallel circuit. The starter sees 12 volts, but the potential energy in amperage is the combination of the two batteries. A flashlight with two batteries is in series, positive to negative (or example, two 1.5-volt D batteries). The voltage to the bulb would be 1.5 + 1.5 = 3 volts.