I have had my fair share of car troubles in my repair shop. One of the most frustrating issues is when the engine cranks but won’t start and backfires.
This problem can be caused by a variety of issues, including the following.
- Broken crankshaft position sensor.
- Worn-out spark plugs
- Misaligned cam chain
- Weak compression in the engine
- Problems with the fuel system
- Exhaust gas recirculation (EGR) System
In this article, I’m going to share my own experiences and insights into tackling this perplexing problem. Whether you’re a novice mechanic or a novice car owner, this guide will help you get your engine running smoothly again.
Engine Cranks But Won’t Start And Backfires | Reasons With Potential Fixes
I can feel that frustration when you turn the key, and the engine quickly cranks, but there’s no roar, just a stubborn silence. And then, the occasional pop and bang of a backfire, as if the engine is teasing you.
This simply means the engine is struggling to make a spark, get fuel, or create the right amount of pressure inside.
Here are the reasons.
Broken Crankshaft Position Sensor
The crankshaft position sensor tells the computer in the engine where the valves and pistons are. The computer uses this to decide when to make the spark plugs work.
If this sensor is broken, the computer doesn’t know when to fire the sparks and risks the engine to start. This makes the fuel and air mix not burn fully, making the engine work poorly or not start at all. Other symptoms include:
- Occasional backfiring during cranking or startup.
- Check Engine Light (CEL) may illuminate, indicating a sensor-related trouble code.
How to fix it?
- Use an OBD-II scanner to check for relevant trouble code P0335, which points to a problem in the circuit of the crankshaft position sensor.
- Get a new crankshaft position sensor and install it with the help of a mechanic.
You can watch the video on how to replace a broken crankshaft position sensor.
Worn-out Spark Plugs
This component plays a critical role in kindling the air/fuel mixture in your engine’s cylinders. When they become worn or fouled, they can misfire or fail to create a proper spark, leading to starting difficulties and backfiring.
New spark plugs usually work well for a long time, sometimes over 100,000 miles. But at times, they stop working early because of oil leaks, dirt, or problems with the ignition coils that give power to the spark plugs.
Symptoms
- Rough idling or poor engine performance.
- Backfiring, especially during acceleration or startup.
How to Fix it?
To fix worn-out spark plugs, you can follow the steps
- Ensure the vehicle is parked on a flat, dry surface and allow the engine to cool.
- Disconnect the spark plug wire, remove the coil on the plug (COP), and use a spark plug socket and ratchet to unscrew the spark plug.
- Install the new spark plugs with care, avoiding cross-threading, and tighten them to the correct torque.
- Reinstall each wire or coil after applying a small amount of plug wire grease to the plug wire boot (or COP boot).
Weak Compression in the Engine
Engine compression is the result of the piston compressing the air-fuel mixture in the cylinder. Low compression levels prevent the engine from starting and cause backfires, as the mixture may not ignite properly. The causes include worn piston rings, damaged valves, or a blown head gasket. Other symptoms are
- Reduced power and performance.
- Backfiring during startup or acceleration.
How to Fix it?
- With the help of a professional mechanic, changing damaged parts with new valve seals, new piston rings, or any other related components should be carried out.
- Repairing low compression issues may require significant engine work, depending on the root cause. Seek professional assistance for diagnosis and repairs.
A Misaligned Cam Chain
If the cam chain isn’t in the right place, it makes the engine crank but not start and also makes a backfire sound in the intake. One perplexing aspect is when the engine temp spikes and then returns normal, which is a result of incorrect combustion due to misfires or incorrect timing.
This happens because the engine’s timing gets mixed up, and the valves open at the wrong time when the spark happens. Two things that can make the cam chain be in the wrong spot are the timing chain isn’t set right and when the timing chain is too loose.
How to fix it?
Seek the help of a skilled mechanic to realign or replace the cam chain to ensure proper timing.
Problems With the Fuel System
These problems include issues with fuel quality, fuel delivery, or components like the fuel pump, fuel injectors, or the fuel pressure regulator. When you try to start your car, and it makes a cranking noise but doesn’t start, it might be because the engine isn’t getting the fuel it needs. One possible cause of this problem is dirty fuel injectors.
How to Fix It?
- Check for fuel pressure using a gauge to ensure it meets the manufacturer’s specifications.
- Consult with a professional mechanic for a proper diagnosis, repair, and replacement of a damaged fuel pump.
- Inspect the fuel injectors for clogs or malfunctions and clean or replace them with the help of a mechanic.
- Ensure that you are using clean, quality fuel with the correct octane rating. Additionally, this can be addressed by cleaning engine sludge with diesel, which effectively removes deposits that hinder fuel flow.
An Aging Car
Older classic cars can have more backfiring problems because they need hands-on adjustments to work right. Unlike new cars that use coil-on-plug designs to control sparks precisely, classic cars often use spark plug wires.
Some older cars also have carburetors, and if these don’t work well, they mess up how much air and fuel mix, causing backfires. It’s important to note that aging car problems often result from a combination of factors. This includes wear and tear, lack of maintenance, and exposure to environmental conditions.
How to fix it?
- Regular maintenance and timely replacement of worn-out parts by a mechanic can help mitigate these issues.
Exhaust Gas Recirculation (EGR) System
A malfunctioning EGR valve can cause exhaust gasses to enter the combustion chamber at the wrong time, leading to backfiring.
How to Fix it?
- Consider seeking help from a qualified mechanic or technician who can perform a comprehensive diagnosis and repair.
Here is a video to watch on how to replace the EGR system.
People Also Ask
Here are questions people also asked on engine cranks that won’t start and backfire and their answers.
What is the difference between misfiring and backfiring?
A misfire happens when a cylinder in the engine doesn’t fire properly, meaning it doesn’t burn the fuel completely. On the other hand, a backfire occurs when the fuel burns outside the cylinders.
What causes sputtering and backfiring?
Sputtering and backfiring issues often result from clogged fuel or air filters. This leads to insufficient fuel or air reaching the engine, causing a lag in acceleration. Efficient combustion in the combustion chamber requires the right balance of air and fuel.
Final Word
An engine that cranks but refuses to start and occasionally backfires can result from various causes, including ignition system faults, fuel system issues, timing problems, and more. To resolve these issues, it’s crucial to systematically diagnose and address each potential cause.
However, tackling these problems can be challenging, and accurate diagnosis requires expertise. Therefore, if you are uncertain about diagnosing or fixing the issue, seeking professional assistance is strongly recommended. Experienced mechanics possess the skills and knowledge needed to pinpoint and rectify the underlying issues, ensuring the vehicle’s reliable performance and safety.
