Can A Bad Alternator Cause Rough Idle, Misfire and Engine Shake?

Have you, in the recent past, experienced rough idling? What did you do? I guess you called your trusted mechanic to fix the problem. Yes, he did the work, but it kept recurring after a few days, right?

Well, dealing with car problems can sometimes be very tricky. However, with some expert advice like (put your company name) offers, you can seamlessly handle the problem. Now, if you check beneath your hood, there is a small component attached via a belt to the engine crankshaft that most people overlook when diagnosing engine problems. An alternator is a critical component that helps in maintaining stability and balance in the auto-electrical system.

The alternator works by inducing alternating current to the auto system by converting mechanical energy to electricity. It consists of copper windings neatly designed to create a magnetic field flux with the rotor ( the rotating element).

As the rotor rotates, there is an induced Current. It lights headlamps, lowers and lifts car windows, and powers some critical engine sensors among other functions. The voltage regulator links with the alternator.

Newer cars are being manufactured with ‘smart’ alternators. These ones can interface with the Electronic Control Unit (E.C.U) for quick and efficient communication. For instance, it achieves instantaneous air-fuel ratios, hence smooth firing order, and stability.

Rough-idling can be a nuisance to the driver and even other occupants. Normally, it occurs when the gears are not engaged, but the engine is running at relatively low RPMs (about 600rpm).

A bad alternator could choke the engine.

Can A Bad Alternator Cause Rough Idle, Misfire & Engine To Shake

Can A Bad Alternator Cause Rough Idle

A bad alternator can cause rough idle. Normally a bad alternator works below its generating capacity. What we mean by this is that an alternator that is supposed to generate 12A, for example, will only manage 10A (Over 20% drops in capacity).

Consequently, it undercharges the battery. The battery in turn supplies less power to the spark plugs. The spark plugs, in normal firing, would ignite the fuel in all the cylinders in an orderly sequence. In a malfunctioning system, some cylinders may not fire appropriately, causing the engine to misfire.

A bad alternator can cause the engine to shake. A misaligned alternator runs rough and jumpy. Besides, loose mountings amplify engine vibrations. Normally, the alternator is supposed to be tight in its socket.

However, with time, the mountings become loose due to frequent knocks and jump as the car moves. The loose connections and misalignments can spread to other vital components like the bearings, hence further damaging the engine. At this juncture, the engine shake is more pronounced.

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A bad alternator can cause rough idling. In fact, rough idling results from the engine misfiring and shaking. A misaligned alternator runs rough. It can also indicate a serious problem is developing in your car. Additionally, when an alternator has a cable loosely connected, it can cause electric sparks as the electric resistance rises sharply.

Due to excess heat, the cooling fan may not be able to dissipate heat efficiently, hence further reducing the alternator’s capacity to run smoothly. Now, how do you identify a bad alternator?

How A Bad Alternator Contributes To Rough Idling

Similar to other parts, you should check the alternator routinely. Rough idling is a phenomenon that occurs slowly but steadily until it becomes more advanced. In this state, the problem goes to the battery. Therefore, it becomes systemic. So how does it contribute to rough idling?

The alternator is a generator of electricity. It, therefore, charges the battery when the engine is running and the battery discharges when the engine starts.

A faulty alternator spreads the problem to the spark plugs. During ignition, there could be milliseconds of delay in engine take-off resulting in misfiring. In normal firing order, the sequence is rhythmic. When there is abnormal firing, the engine will run rough and jumpy.

Due to alternator misalignments, running will be asynchronous with the engine. A properly working alternator should rotate smoothly as it tunes with the engine RPMs.

Misalignments, if unchecked, could cause bearing failure further compounding the problem. Overheating and vibrations are common at this juncture. Even at low speeds, vibrations can cause a great disturbance to other parts like the crankshaft.

A faulty voltage regulator can cause either undercharging or overcharging. The headlamps tend to be sharp at high RPMs but blurred at low RPMs (an indication of a regulator problem).

Additionally, overcharging makes the battery swell and become a fire risk if left unchecked for a long period. At low RPMs, due to less power from the engine, rough idling becomes more pronounced.

Due to excess charge generation, there will be excess heat generation as well. It could interfere with the cooling system as it gets overworked to the point of failure.

At this juncture, thermal stress also peaks hence failing the clamps and joints. A loose component will greatly contribute to vibration and rough idling.

Too much heat also interferes with the cabling. Power cuts prematurely, hence further damaging the battery and spark plugs.

A bad alternator delivers insufficient power to other critical components such as sensors. In modern cars, there is an inbuilt crankcase position sensor.

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A wrong crankcase positioning due to wrong signal processing will contribute to cylinder misfiring hence roughing it up.

Besides, wrong signal processing contributes to incorrect air-fuel mixing. This E.C.U is supposed to regulate the mixing by relying on the engine power demands. If demand is high, the E.C.U. is supposed to allow more fuel to mix with enough air, hence a rich mixture.

However, a faulty alternator will deliver less power to the E.C.U causing it to malfunction. Black smoke at the tail end of the exhaust system (at high power demands) indicates a lean mix.

How to Identify a Bad Alternator

However, before we demonstrate how a bad alternator contributes to rough idling, the following are some of the symptoms that qualify the bad state:

1. Do you smell burnt rubber?

A faulty alternator would try to work to its capacity regardless of the resistance from the damaged electrical wires. If it goes beyond the limit, some parts of the wire could burn.

2. Whining sound underneath

When the engine is running in idle mode, you can hear the sound. If abnormal sounds like squeaking or whining are heard, it could indicate a systemic problem.

3. Loose clamps and bolts

Loose clamps and bolts further add to the abnormal sounds as they tend to cause the alternator body to vibrate.

4. Engine RPMs at idling are below 600rpm

A faulty alternator denies the Electronic Control Unit (E.C.U) the capacity to send accurate commands to the carburetor. It then affects the air-fuel ratio mixing as it depends on the engine demands (as communicated by E.C.U hence reduced spinning). Most modern cars should comfortably idle somewhere between 600 and 1000 RPMs. Anything below 600rpm at idling is considered abnormal.

5. Belt and pulley conditions are poor

Cracked worn-out belts lower power transmission efficiency by slipping. The alternator is deprived of energy to function optimally. Pulleys age in grooves hence belt misalignments.

6. Low belt tension

When the belt is loose, the transmission becomes less efficient as less mechanical power is transmitted to the alternator. You should check the tension of the belt regularly and fix it.

7. Misalignments with the crankshaft

Misalignments can either be horizontal or vertical. It occurs when the crankshaft axis is not in-line with the pulley axis. Also, when the driven pulley (attached to the alternator) is not in the same plane as the pulley.

A misaligned rotating element lowers power transmission and contributes to excessive vibration and rough idling.

8. Loose cables and damaged fuse

Zero current flow indicates a damaged fuse. We can use an ammeter to check this. Loose cables contribute to more resistance as they tend to open the circuit. It is risky to have loose cables as they can easily cause a fire.

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9. Faulty voltage regulator

Now, if you check on the dashboard, there are readings. If the readings fluctuate over a short period, then it can easily indicate a faulty regulator. A correct reading should not go beyond 14.7 volts.

10. Damaged cooling fan

The fan is used to dissipate heat from the alternator. However, a damaged cooling fan would cause temperatures to rise hence further damaging the alternator.

11. Lifting window is a nightmare

If you notice that the windows are lifting or lowering very slowly and it has to be a struggle, then something could be wrong with the alternator.

Removing The Rough Idle By Fixing A Bad Alternator

Rough idling is a rapidly developing problem that can lead to catastrophic failure if it is not properly handled.

In case you are wondering how to fix the alternator, here is a practical guide that could help. However, if you are not confident enough to handle it yourself, you can seek professional help.

Step 1: Isolate the alternator

Before you start removing the alternator from its fixed position, make sure that you park the car safely. Also, make sure that all safety gear and tools are on site. Safety gear could be hand gloves, boots, and overalls. The tools and equipment you must use include a ratchet, wrench, hydraulic jerk, and digital voltmeter.

Remember, safety is our number one priority. Make sure the car engine is cold before you start working. Lift the car with a jerk attached at the correct points.

Make sure the car is in a stable position and the handbrake is engaged. Any movement of the car at this position could result in a fatality.

First, isolate the battery from the alternator by unbolting the negative terminal (put on hand gloves). Keep cables away from the alternator to avoid entanglements and damage.

Next, disconnect the alternator by removing the power cable. It is a thick black cable, and you remove it by unscrewing it.

Step 2: Remove the serpentine belt

Most cars have auto-tensioning mechanisms. Using the correct ratchet size, loosen the tension bolt to remove tension. Now, you can remove the belt.

Check its condition.

A damaged belt has cracks on its contact side with the pulley. Replace the belt if its condition is bad.

Step 3: unbolt the alternator from its bracket

Lose the bolts but don’t remove them. If there is no auto-tensioning then by loosening the bolts, you can easily release the belt at this juncture.

Some modern cars have the alternator deeply buried underneath. You should work safely in this limited space to avoid injury to yourself and damaging fragile parts like the sensor and sensor cables.

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Step 4: Remove the alternator from its socket

Carefully slide the alternator from its socket. Make sure you do not entangle the power cable by placing it away from the alternator’s space.

After removing it, check and compare it with the new one. If you notice some parts missing in the new alternator, kindly wrap them and send them back to the vendor.

Besides, you should test the new alternator once fixed and check its performance and compare.

Step 5: Fit the new alternator

Once verified, you can start fitting it. It should now be simple as you now reverse the above procedure.

Carefully put it in its place by lowering it to its socket and sliding it to its position and bolting. Do not tighten the bolts at this juncture if there is auto-tensioning.

Put back the belt by making sure it goes around to every component ( as was the old one). You should put pressure on the alternator as you tighten the bolts using a ratchet until tension is enough.

Check alignment and adjust accordingly. Alignment is both vertical and horizontal. Remember, the belt tension should be enough to facilitate power transmission to the alternator.

Fix the power cable. You should be able to pin it to the correct port as was the old one.

Step 6: Connect the battery to the alternator

Reconnect the battery cable to the negative terminal. Now the alternator is ready to work. Make sure the battery terminals are clean before reconnecting the terminals. Be careful not to electrocute yourself.

Lower the car by slowly releasing pressure in the hydraulic jerk.

Step 7: Test the new alternator

Still, in idling mode, start the engine and let it run for a few minutes (about 5 minutes). Now, connect the voltmeter by touching the red cable pointer to the positive terminal of the battery and the black one to the negative terminal. It should read about 12.6 volts.

Now, run the engine and measure the voltage. Should be between 14.2 and 14.7 volts. If above 14.7, then the battery is overcharging while any reading below 14.2 indicates undercharging.

Besides, the lights should not fluctuate as the engine runs. We should also expect a smooth rotation of the alternator.

Above all, make sure bolted components are fitted correctly to minimize engine noise and vibration.

Winding it up

Rough idling can be very costly to remove. It requires a proactive approach as it is systemic (in other words, it spreads problems to other parts like covid-19). We routinely inspect our Auto components and parts so that we can detect problems at the earliest time. Besides, rough idling can severely affect engine performance, hence increasing fuel consumption.

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1. What is the quickest way to tell if my alternator is bad?

A bad alternator exhibits several symptoms. With a voltmeter, you can test the battery while the engine is running. It should read between 14.2 and 14.7 volts. Any value below or above this range indicates undercharging and overcharging (a quick way to tell that the alternator is performing poorly).

2. When should I replace my alternator?

Although alternators have a relatively long life. You should replace it as soon as the symptoms discussed above start manifesting. A bad alternator can both be very costly and risky.

3. How much will I spend on replacing an alternator?

It can vary depending on the severity of the work and the car model. Some alternators are hidden underneath. Removing them can be very tiresome. A new alternator costs between 180 to 250 dollars. Adding labor costs could shoot it to about 400 dollars (on the higher side).

4. What are some of the maintenance activities I can do on my alternator to prolong its life?

Once an alternator rates bad, you should never try to use shortcuts and quick fixes. Do not gamble with your toy and life! (no pun intended). However, following procedures correctly should properly fit a new alternator. Avoid loose connections and misalignments.

5. Can a bad alternator damage the battery?

Absolutely. A bad alternator either overcharges or undercharges the battery. Too much charge causes the battery to swell, hence becoming a fire risk.

6. How do I identify a genuine alternator? How do I distinguish between a fake one?

You should contact a professional to help you select a genuine alternator. Sometimes, as a customer, it can be challenging to distinguish a fake from the original.

7. Where is my alternator located?

Most alternators are easy to locate. To locate it, just identify the serpentine belt and follow it down to where it attaches the alternator to a pulley. It transmits mechanical power from the crankshaft to the alternator when properly tensioned.

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