Rick's Free Auto Repair Advice

Car won’t start, cranks but won’t fire up

Step by step for a engine cranks but won’t fire up condition

IF the engine cranks but won’t fire up, ALWAYS start by checking the immobilizer (SECURITY) light in your car. Some immobilizer designs cut off fuel to prevent theft. If the light is flashing, get that checked out by a shop before proceeding with any of these tests.

If you turn the key and the starter engages and rotates the engine but the car won’t start,  this post is for you. Let’s divide the topic into these three sections:

Step 1 If you own a Ford Ford, Mercury, Lincoln vehicle and it cranks but won’t fire up, START with Step 1.

Step 2 Car cranks but won’t fire up when cold

Step 3 Car cranks but won’t fire up when warm or hot

STEP 1: For Ford vehicles ONLY—Engine cranks but won’t fire up

Most Ford, Mercury and Lincoln vehicles are equipped with an Intertia Fuel Cutoff Switch. The switch is designed to shut off power to the electric fuel pump if the vehicle is in an accident or is struck. The switch can activate even if another car barely touches your in a parking lot. If you own a Ford, Mercury or Lincoln vehicle and the engine cranks but won’t start, ALWAYS try resetting the Intertia Fuel Cutoff switch as your first step.

Click here to find the location of the Intertia Fuel Cutoff Switch in your Ford, Mercury or Lincoln vehicle

Press the reset button and try starting the engine. If that doesn’t work, proceed to these next steps

Step 2: Car cranks but won’t fire up when cold

This is really tough to diagnose with no diagnostic tools. However, let’s take a look at the basics. To start a cold engine you need:

• The right cranking speed, ie, is the battery fully charged

• The right air/fuel mixture with fuel at the right pressure

• Spark plugs that are in good condition

Let’s start with the battery

Check #1) Do you have a fully charged battery

Cranking speed is directly related to the battery charge, battery temperature, the quality of the electrical connections and the proper viscosity oil. You know the sound your engine makes when it’s cranking normally.

If the engine is cranking much slower than normal, you may have a discharged battery.

Turn on the dome light and try cranking the engine. If the dome light dims to almost nothing, that’s the sign of a dead battery. Call for a jump.

Check #2) Do you take short trips in cold weather or not drive for long periods?

All maintenance-free (most common type sold and installed today) lead acid batteries self discharge at the rate of 0.5% per day at room temperature. However, car computers constantly draw a small amount of current to keep memory alive and to be at the ready state when you operate your keyless entry fob. That small current draw, combined with self discharge and long idle times can kill a car battery. If haven’t driven your car for 30 days in cold temps, chances are very good the battery is discharged. Try getting a jump start.

If you haven’t driven the vehicle in more than 30 days AND the weather has been below freezing, chances are VERY good your battery has not only discharged, but FROZEN. A frozen battery cannot be brought back to life and must be replaced.

If you drive short trips in freezing conditions, chances are your battery is discharged. This happens when you start your car in cold weather, turn the blower/defroster to high, turn on headlights, rear window defogger and seat heaters and drive at low speeds for less than 20-minutes. Your car’s charging system simply can’t output enough power to run all those electical accessories AND recharge the battery. Bottom line: you’re pulling more power out of the battery than you’re replacing.

To keep your battery fully charged in cold weather,  you must DRIVE IT

At least once per week: Start the engine and drive it at highway speeds for at least fifteen minutes with the seat heater, rear window defogger turned off and the blower motor set to the lowest speed. That reduce the electrical load to allow the alternator to fully recharge your battery.

Check #3) Is the battery frozen?

Car battery acid stratifies when sitting idle for long periods

Acid stratification is also a factor in the state of charge of your battery. Battery electrolyte is composed of approximately 35% sulfuric acid and 65% water. When a battery isn’t used regularly, the acid, which is heavier than water, falls to the bottom of the battery. That leaves a very low concentration of acid near the top of the battery. This condition is referred to as acid stratification. It’s the sulfuric acid that prevents a battery from freezing in cold weather. When the battery experiences acid stratification, it is more prone to freezing. In fact, the top acid/water layer can freeze at or near 32°F. That permanently damages your battery. Check the sides of the battery for signs of bulging. If the sides appear bulged, the battery is toast. Do NOT try jump staring the engine. Buy a new battery.

car battery acid stratification

In summary, the longer you let your battery sit unused, the more likely it will be low on charge. If you leave it discharge in cold weather, you dramatically increase the chance of it freezing.

Check #4) Is the fuel pump working?

Fuel injected engines retain fuel pressure at all times so the engine can start up after long periods. The fuel pressure is maintained by a check valve in the fuel pump. When the check valve fails, the fuel drains out of the fuel rail on top of the engine overnight and you have a hard time starting it in the morning when it needs maximum fuel. As a result, you have to crank the engine for much longer because the fuel pump needs more time to build to the proper fuel pressure. When that happens the engine will crank and crank and it make take several tries before the engine starts.

Listen for fuel pump prime

Turn off the blower motor and radio. Turn the key to the RUN position (not the START position) for 2-seconds. Listen for the sound of an electric motor coming from the fuel tank area. If you hear the fuel pump run and then stop after 2-seconds, that’s a sign the pump is running. If you hear nothing, you may have a bad fuel pump.

Check 5) Do you have enough fuel pressure?

When you shut off your engine, a check valve in the fuel pump prevents the fuel at the engine from draining back into the tank. Fuel pressure should remain within 5-10 psi after sitting all night. Unfortunately, check valves can fail in extremely cold weather. When that happens, you get into your car and try to start the engine when it has NO fuel pressure. Since the battery is low on charge at a time when the engine needs even more power, you drain the battery trying to start with no fuel. By the time the fuel pressure builds, the battery may be so low that it can’t crank the engine fast enough to fire.

What to do? If you have any indication that it’s taking longer for your engine to fire up, try this:

Turn the key to RUN, but don’t try to start the engine. Turning the key to the RUN position commands the fuel pump to perform a 2-second “prime” cycle. Turn the key to OFF. Repeat this procedure three times. That should fully pressurize the fuel rail and fuel injectors. Then try to start the engine. If it starts right up, that’s an indication your check valve is failing. Get the fuel pump replaced immediately.

fuel pump cutaway showing turbine, motor and check valve

Turbine style fuel pump showing the turbine, motor and check valve

 

 

 

Check 6) Wrong air/fuel mixture heck the engine coolant temperature sensor

Cold engines need a much richer mixture before it can ignite. A faulty or dirty Mass Airflow Sensor (MAF), manifold absolute pressure sensor (MAP) or engine coolant temperature sensor (ECT) can cause the computer to calculate the wrong air/fuel mixture. These sensors are hard to diagnose without a professional grade scan tool. But there are three things you can try if your car won’t start:

Check the engine coolant temperature sensor

Try depressing the gas pedal halfway and then cranking the engine. The computer is supposed to calculate the right air/fuel mixture with your foot off the gas pedal. If it’s getting bad information from a bad or failing sensor, depressing the gas pedal will OVERRIDE the factory programming and force the computer to add more gas.

Check for a flooded engine

If you’ve cranked the engine for long periods without starting, you may have flooded the engine. Depress the gas pedal to the floor and HOLD IT THERE while cranking. This procedure tells the computer to stop adding fuel and opens the throttle plate all the way to let more air into the engine. If you get any indication that the engine wants to fire up, immediately release the gas pedal.

Check and clean the MAF sensor

Clean the MAF sensor with MAF sensor cleaner. See this post on how to do the cleaning.

Add fuel to the throttle body

Use starting fluid. Unhook the air intake tube from the throttle body and spray starting fluid directly into the throttle body. Then try starting the engine. Don’t overdo it on the starting fluid. You can flood an engine by spraying in too much.

Check #7) Did you fill with winter blend fuel?

Winter gasoline is more volatile than summer blend gasoline. If your tank is filled with summer blend gasoline, you may have a hard time starting it in very cold weather. Adding “Heat” moisture control additive won’t change the fact that the summer gasoline isn’t as volatile. If you have a tank of summer gas and your car won’t start, getting it towed and stored in a warm shop may help. Once you get it started, add fresh winter fuel and drive a long distance to use up the old fuel.

Is your gas line frozen?

Naw. Modern fuel with ethanol and tightly closed fuel tanks have pretty much eliminated gas line freeze-up. Ethanol is water loving, so it absorbs any moisture in your tank. Modern fuels contain 10%-15% ethanol, so you really don’t have to worry about gas line freeze up.

Not convinced? Think about this: Many DIYers think they can add a 16-oz. bottle of “Heat” to fix the problem. If you have a 20-gal tank and the gas is 10% ethanol, you’ve already got 2 GALLONS of alcohol in your tank. Adding another pint won’t make ANY difference. Trust me, you don’t have that much water in your tank. The fuel tanks in modern don’t let in that much moisture.

However, ethanol fuels can experience “phase separation,” where the ethanol and water separate out from the gas. Since water is heavier than gas, the ethanol/water settle to the bottom of your tank. In other words, your engine is sucking water instead of gas. But even then, the ethanol will prevent freeze up. If the gas in your tank is old, that may cause a no start problem. But adding alcohol won’t fix. it.

Step 3)  Car cranks but won’t fire up when warm or hot

Check #1) If you own a Ford, Mercury or Lincoln vehicle check the crankshaft sensor operation

Ford vehicles have a built in check for crankshaft position sensor operation. Here’s how to check it. Watch the Check Engine Light or Service Engine Soon light while cranking. Ford has built a mini-self diagnostic test into their Check Engine light. The light will come on as soon as you turn the key to start. It will stay on while cranking until the computer receives a good signal from the crankshaft sensor. Then it will turn off. If the Check Engine light stays on the entire time you’re cranking your Ford vehicle, the computer isn’t getting a good signal from the crankshaft sensor and the engine will NOT start. Call a tow truck.

Check #2) See if the engine is flooded

An engine can flood with gas if the fuel injectors are leaking or, if the engine started and then immediately died. There’s a way around this; it’s called “Clear Flood Mode.” To activate clear flood mode, press the accelerator all the way to the floor and hold it there while cranking the engine. DO NOT PUMP the pedal, that’ll make the flooding even worse! After several tries cranking with your accelerator held firmly to the floor, release the pedal and try starting the engine. If it starts, that’s an indication that it was flooded.

Check #3) Do you have spark?

Worn spark plugs can cause a “cranks but won’t fire up condition.” Worn spark plugs produce a weak spark that’s not hot enough to ignite cold fuel. If you haven’t changed your spark plugs according to the car makers recommendations, they can leave you with a car won’t start when cold or worm condition. Worn plugs can be hard to diagnose without the proper tools.  If you have the facilities and tools, install new properly gaped spark plugs, along with new spark plug wires (if equipped).

©, 2018 Rick Muscoplat

Posted on by Rick Muscoplat

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