Rick's Free Auto Repair Advice

Car won’t start —Engine cranks but won’t fire up

Engine cranks but won’t fire up

Here are the most common causes of an engine cranks but won’t fire up condition:

• Blown fuel pump fuse
• No fuel pressure or low fuel pressure
• Bad engine coolant temperature sensor
• Flooded engine
• Worn spark plugs

No fuel pressure or low fuel pressure

IF a fuel injected engine doesn’t have the proper fuel pressure, it won’t start. To maintain fuel pressure, carmakers install a check valve in the pump that prevents all the fuel from draining back to the tank. All fuel systems lose some pressure overnight, so carmakers include a 2-second “prime cycle” to rebuild about 5-10-psi. to enable a quick start. If the check valve fails, it’ll take almost 10 full seconds of running to rebuild pressure.

How to test your fuel pump and check valve

• Turn off the radio.
• Turn the key to RUN, but don’t turn to START.
• Listen for a 2-second “humming” sound coming from the fuel tank.
• Repeat the key turn at least three times. Then try starting the engine.

If it starts right up, that’s an indication of a failing check valve. Have a fuel pressure leakdown test performed by a shop.

If you don’t hear the pump “prime,” check the fuel pump fuse.

If the fuel pump fuse is good, but the engine still doesn’t start, try this

• Remove a shoe
• Crawl under the vehicle just enough to reach the fuel tank. Smack the bottom of the fuel tank a few times. Then try starting the engine. If it starts, that’s an indication of a flat spot on the fuel pump motor armature. Have a shop replace the fuel pump

Bad engine coolant temp sensor

Your car’s computer determines the proper air/fuel mixture based on ambient temperature, engine coolant temperature, and barometric pressure. The most common failure in this system is the engine coolant temperature sensor. If it’s off, the computer will think the engine is warmer than it really is and it won’t provide enough fuel to start a cold engine.

To test the engine coolant temperature sensor, partially depress the gas pedal and hold it there while starting. A partial gas pedal will override the computer and provide more fuel to the engine. If the engine starts, have a shop test and replace the engine coolant temperature sensor.

Is the engine flooded?

Computer operated engines don’t flood often. An engine can flood if you don’t drive much and your fuel tank is still filled with summer gas in the winter or winter gas in the summer. To start a flooded engine, depress the gas pedal all the way to the floor and hold it there while cranking the engine. This puts the engine into “clear flood mode” and the computer shuts off the fuel injectors so the cylinders can dry out. After cranking in clear flood mode for a while, release the pedal and try starting again. If it starts up after performing the clear flood routine, have the fuel system check for the presence of old fuel.

If your hard starting problem happens on a hot or warm engine, the flooding can be caused by leaking fuel injectors than release raw fuel into the cylinders after engine shut down. If the clear flood procedure works to start your engine when it’s warm, you may have leaking fuel injectors. Try adding a fuel injector cleaner like Chevron Technron or RedLine Fuel System cleaner

Do you have worn spark plugs?

Worn spark plugs may worn fine once the engine is warm, but cause no start issues when the engine is cold. If you’ve done all the tests above, check your maintenance schedule to see if you’re overdue on spark plug replacement.

©, 2020 Rick Muscoplat


Posted on by Rick Muscoplat


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