How to Diagnose Your Car When It Has Power But Won’t Start

“Why won’t my car start but I have power?” It’s a question that has troubled many car owners at one point or another.


There are many reasons why this happens. One of the most common causes is a bad spark plug. Spark plugs deliver electric current to your car by igniting the air-fuel mixture in the engine’s cylinders in order to start it. 


If your engine is holding compression without issues and there are no problems with the fuel system, then your spark plugs are causing it not to start.


Of course, that’s not the only answer to this car issue—there are many others. We’ll enumerate the common questions related to this problem and how you can diagnose it.

1: What are the Signs of a Failing Spark Plug? 

Signs of a Failing Spark Plug

Bad spark plugs could be the culprit for why your car won’t start, as we’ve mentioned earlier. But how do you diagnose it?

You don’t have to wait for your car not to start to know if your spark plugs are starting to fail. There are signs and symptoms you can watch out for so you can remedy the problem before it gets out of hand:

Loud Engine

A loud rattling noise coming from your engine is one of the signs of a malfunctioning spark plug. When a spark plug is starting to go bad, it reduces the efficiency of your engine’s cylinders, causing them to rattle.

This, in turn, overworks your cylinders. If it doesn’t get fixed in time, it could cause more problems—expensive ones—down the line.

Engine Misfires

When you’re on the road, do you feel your car jerk sometimes? When your engine’s cylinders are not firing properly, it momentarily cuts out, causing your car to lose its pace before catching back up.

Engine misfires are caused by many things—leaky valves, low-quality fuel, or you guessed it—failing spark plugs.

Your Car Fights to Accelerate

One of the obvious signs that your spark plugs need to be replaced is when your car seems to be fighting to accelerate. When left unchecked, this situation could be dangerous, so when you start experiencing this, it’s a sign you need to see a mechanic right away.  

High Fuel Consumption

When your car’s spark plugs are in poor condition, they can’t efficiently burn fuel in the combustion chamber. When this happens, your engine will need more fuel to perform properly. If you notice your car eating up more fuel than usual, your spark plug might be the culprit.

The “Check Engine” Light is On

If your spark plugs are blistered from running too hot, are covered in oil, or are problematic in some form, they will cause problems for the engine. Check if the engine light on the dashboard is on. It’s a sign that it’s time to visit a mechanic.

2: How Can You Tell If It’s Your Starter, Battery, or Alternator?


How Can You Tell If It’s Your Starter, Battery, or Alternator

It could be the spark plug that’s causing your car not to start, but it could also be the battery or alternator. How could you tell which is which? There are several ways to know:

Signs That It’s Your Starter

A bad starter will produce a clicking sound when you turn on the ignition. Your car won’t start, but the dashboard lights will come on. In some cases, you’ll see smoke come out from under the hood!

Sometimes, your car engine won’t ignite on the first attempt but will start on the second. If you’re experiencing intermittent problems starting your car, it could be an issue with the starter relay.

Signs That It’s Your Battery

When you try to start your car, do you hear clicking sounds? Ignition clicks are one of the signs of a failing battery. But oftentimes, there won’t be any sound at all.

The battery creates a charge for the starter so it can crank the engine. However, when the battery doesn’t have sufficient energy, all you’ll hear is a clicking sound but the car will fail to turn over.

Another sign of a dead battery is if a jump starts your car but won’t turn over again once it’s shut off. You’ll notice corrosion on the connectors and warping or swelling in the battery case.

Signs That It’s Your Alternator

If your car is exhibiting these symptoms, a bad alternator might be causing the problem:

       The smell of burning rubber (it means your alternator wires have overheated);

       A growling sound before the car dies;

       Flickering headlights and interior lights;

       Jumping the car enables a start, but dies off immediatel

3: If It’s Not the Starter, Battery, or Alternator, What Else Could It Be?

If you have checked your spark plugs, battery, and alternator and they’re all working, what else could it be? What could be causing your car to fail to start even though it has power? Here are a few possible answers:

Defective Transmission Range Selector Contact

There’s a range selector (also called neutral safety switch) located within the automatic transmission shifter. When it has poor electrical contact, the engine won’t be able to know whether the car is in “Neutral” or “Park” which causes your vehicle to fail to start.

Insufficient Compression

To run under its own power, your car needs fuel, air, spark, and compression. When any of this is missing or insufficient, your car could be difficult or could fail to start.

An engine with low compression means it might have leaky seals and gaskets. You may need to replace them and/or other components such as piston rings to make your car start.

Clogged Fuel Injector

Does your car crank when you turn the key but the engine won’t start? If that’s the case, then it’s possible fuel isn’t getting to the engine because of clogged fuel injectors.

Fuel injectors are typically located in the intake manifold right at the head of the engine. Over time, they corrode and get filled with rust and other debris. When this happens, the fuel injector won’t be able to add the right amount of fuel to the cylinders which cause your car to fail to start.



Pro tip: You can keep your fuel injectors clean longer by using only high-quality gasoline.


Defective Wiring

There’s more than one wire running from the switch going to the starter. All these wires must be in good condition for your car to start.

For example, if the wire from the ignition switch going to the starter solenoid is disconnected while you’re driving, your car will stall. Diagnose the issue by examining all the connections and electrical wiring to rule it out.

Bad Fuel Pump Relay

Another possible reason why your car won’t start even though it has power is a bad fuel pump relay. A fuel pump relay’s job is to relay the power needed to draw the right amount of fuel to your engine. You can find this component of your car in the fuse box.

Failing to start isn’t the only sign of a defective fuel pump relay. It could also be stalling, inconsistent acceleration, and stalling of the engine.

Maintenance is Key

Some of the symptoms are similar and could be hard to detect by a professional. When neglected, these symptoms—whether from a dead battery or faulty starter—could lead to more significant problems.



You don’t want your car to fail to start when you’re in a hurry or late for an important meeting or event. To avoid the hassle and expensive repairs down the line, make sure your car is regularly checked by professionals.

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