Tech Corner: What Was That?! Diagnosing Engine Noises

We’ve all started up our cars, driven them around and heard it: the dreaded squeal, ping, pop, knock, tick, or bang. And we’ve all asked ourselves “What the hell was that?!” Frightening engine noises will never stop sending chills down your spine, but being able to pinpoint what that sound means is the first step to proper repair. True, there are many ways to diagnose engine problems, OBD systems being the official go-to method. However, many times the beast itself will tell you what’s going on—loud and clear. By being able to identify engine noises, you can make quick work of the troubleshooting process.


Home/Professional Job

Nothing in the world is more terrible than hearing an engine scream like an Old Irish banshee when it fires up. But as annoying (and terrifying) as it can be, the culprit is usually just an old and worn-out belt slipping, which is often an easy fix. Replacing a serpentine belt requires little more than basic hand tools and can be done pretty much anywhere at any time. So, if you consider yourself a pretty handy amateur mechanic, there’s a good chance you can handle this repair at home.

However, accessory pulleys can cause a similar sound—and that makes things a little more difficult. Engine accessories generally aren’t that hard to replace, but some may require specialty tools to be used in the process. A bad alternator or power steering pump aren’t a big deal, but an AC condenser may warrant professional help.


Home Job/Professional

Detonation is a sound that’s pretty easy to identify and pretty easy to fix. When the fuel in the chamber combusts before ignition, this is known as detonation and it gives off a pinging noise. Timing and octane play into this occurrence. Running too hot of a spark plug, using the wrong octane, and potential timing issues can generally be addressed at home with older model vehicles. With newer cars, however, it can be an extensive process to crack into the timing and plugs, so you may want to consider seeking out a professional.


Home Job

This section is dedicated to all of the times we nearly crapped our pants when an old truck, car, or dirt bike backfired on us for. Even when you are first putting an engine together and are expecting it to backfire, it can still stop your heart.

With computer-controlled timing, backfiring isn’t much of an issue in newer vehicles. In older cars though, if the distributor is too far advanced, the backfire can come through the carb. This is easily identifiable as a fireball usually shoots out of the tail pipe. If the distributor is too far gone, the engine will backfire through the exhaust, which makes the bang. When faced with either one of these instances it’s as simple as adjusting the distributor appropriately.

“Tick, tick, tick, tick, tick”

Home Job/Professional Job

Loud ticking almost always indicates an issue in the valvetrain. Ticking in the top end of the lifter is usually a direct indication that a lifter is defective. This is an easy fix, but it will require having to crack into the engine. Ticking can also indicate that the valve lash needs to be set, which is actually a very easy job. In the worst case scenario, it can mean the cam is done for and then you have a big job on your hands.

Start with the simplest solution and work your way forward if you’re tackling this on your own. It can be something as simple as low oil levels or dirty oil that isn’t allowing the lifters to do their job. If the ticking continues even when this is addressed, it’s time to bring in the big guns and see a mechanic.


Professional Job

Of all the alarming engine noises, knocking is the one that truly makes my stomach drop. Even if it’s not my engine, I can’t help but feel sorry for the car owner. Knocking is usually caused by the failure of one or more of the main crankshaft-connecting bearings. And sorry to say it, but this is the bad one… the swan song… the death knell. The repair process requires the bottom end of the engine to be accessed and can be very expensive if machine work needs to be done. The rod bearing must be replaced and all other affected components will need to be fixed as well. This is a major expense and depending on how bad the damage is, it may warrant replacing the engine entirely.

Additionally, if the connecting rod itself is slapping around, things are dire indeed. When a rod is thrown, it’s always best to expect the worst case scenario and prepare for an engine swap. Regardless of what exactly is causing the knocking sound, if you hear it: get yourself to a mechanic stat.

Most shops and professionals will be able to hear these engine noises and tell you what’s going on right away. So, if you’re looking to learn how to repair vehicles, diagnosing these sounds is a good first step in understanding the fundamentals of engine operation. It certainly takes some experience to get a full grasp of all the possible causes, but that trial and error is what turns a greenhorn into a black thumb.

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