Rick's Free Auto Repair Advice

Car wont start but has power

Car won’t start but has power

If you think your car won’t start but has power, the question is how much power? Having enough power to light your dash lights and radio doesn’t mean you have enough power to run the starter motor. Dash lights and the radio take maybe 5 amps. But a starter motor on a cold day takes upwards of 150 amps.

So let’s get down to measuring power

How much power do  you need to start your car?

Using a voltmeter connected to the positive and negative multimeterbattery terminals, you need at least 12.2 volts to even begin to turn the starter motor. If the reading is less than that, your battery is discharged enough that it probably won’t start your car.

If your battery reads 12.2 or more volts, here are some things to check.

Car won’t start but has power yet there are NO sounds when you turn the key

You turn the key and hear nothing, not even a click.

Battery cable connection

Sometimes battery corrosion is easy to spot. But other times your battery cables can look perfectly fine but still not have good contact. If you try to start the engine and have no noise, a single click or rapid clicking, start by cleaning the battery terminals and battery posts.

Bad Ignition Switch

Some makes and models are known for ignition switch problems. For example; 90’s Hondas and late 90’s and early 2000 GM vehicles had bad ignition switches. Just because they turn on the dash lights doesn’t mean they’re switching power the starter. To diagnose a bad ignition switch, you’ll need a wiring diagram and a multimeter.

Car won’t start but you hear Rapid Clicking when you turn the key

A rapid clicking, sounding almost like a machine gun, is a sign of a weak battery or bad battery cable connections. The battery is providing just enough power to pull the starter drive towards the teeth in the flywheel, but not enough power to hold it in place and turn the starter. To learn more about why this happens, see this post. This can be the sign of a weak battery or corroded battery terminals that are reducing the power to the starter motor. Clean the battery terminals. In an emergency situation, try tapping the battery terminals with the heel of your shoe. That may move them just enough to reestablish good contact. If the engine starts, make sure you get it to a shop to have the battery inspected and the battery terminals cleaned.

Rapid clicking sounds like this:

At least this tells us the ignition switch is sending power to the starter relay and starter motor.

Car won’t start and you only hear a Single Click but no cranking

Dead battery, bad battery connections OR dead starter motor

Turn on the dome light and try again. If the dome light dims to almost nothing when you turn the key to START, that can be a sign of a dead battery, corroded battery cable connections or a shorted starter motor. A good battery should easily keep the dome light lit strongly while trying to crank the engine. Test the battery condition with a multimeter; it should have at least 12.2 volts. If it does, then try cleaning the battery terminals.

If you’re stuck away from home and don’t have the tools to clean the battery terminals, continue to turn the key to START 6 or 7 more times. Then let it sit for about 5 minutes. If the problem is the battery, the repeated starting can cause the battery to heat up enough to get you enough power to turn the starter motor.

However, if you detect a burning smell, stop immediately. That means the starter is dead and you’re cooking the starter motor coil windings. (Not that you care that much, because you’re going to have to replace it anyway. But continuing to turn the key can start the motor windings on fire.

Car won’t start but the starter makes a high pitched Whirring Spinning sound

That’s the sign of a failed starter motor drive gear. The starter must be replaced. But many times you can get it to start by turning the key to START 5 or 6 more times. That heats up the grease inside the starter motor drive, allowing it to engage. That may buy you one more start. But that trick won’t work forever, so drive it right to the shop and have them replace the starter motor.

Car won’t start but the engine does Crank— it just won’t fire up

If the engine cranks as fast as it normally does but won’t fire up, that can be a sign of a bad sensor, an ignition system problem, low or no fuel pressure, a problem with your anti-theft system (SECURITY light blinking), the engine is flooded or a mechanical issue is present.

If you own a Ford vehicle, turn the key to the RUN position and wait for the Check Engine light to come on. Then crank the engine. The light should go out while cranking. If it does, that means the computer is getting a good signal from the crankshaft position sensor. If the light stays lit, start your diagnosis with that sensor.

Next, check the inertia fuel cutoff switch. This is fairly exclusive to Ford products. It’s designed to turn off power to the fuel pump if the vehicle is ever involved in a crash. But the sensor can also activate if someone bumps your car in a parking lot. It’s in a different place for each Ford model. So get out your owner’s manual. Find the location and press the reset button.

Next, try starting the vehicle by holding the gas pedal down part-way. If that helps at all, chances are you have a failing engine coolant temperature sensor. Those sensors can fail partially—not enough to set a check engine light, but enough to throw off the computer. The failed sensor makes the computer think the engine is warmer than it really is. So it provides a very lean mixture to a cold engine. By pressing the gas pedal, you override the computer’s commands and force it to provide more gas. If that works, test or replace the sensor.

If the engine isn’t getting fuel, you’ll have to perform a fuel pressure and fuel volume test and that requires special tools. Not a job for a DIYer.

Car starts and dies

This can be caused by a dirty or failed idle air control valve or a vacuum leak or a myriad of other problems. The idle air control valve regulates how much air comes into the engine when you’re at idle. If it’s not working properly or the passages are dirty, the engine will either have too much air or will be starved for air. A vacuum leak can also cause an engine to die after starting because the leak dilutes the rich mixture the computer is providing.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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