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Figuring out Engine Knock

Why Does My Engine Knock? 3 Possible Explanations.

There are a few different reasons your engine might make a knocking, ticking or pinging sound. Let’s break each down and talk about what might be happening.

Is it an engine knocking sound, tick or ping?

One driver’s knock is another driver’s tick. Or ping. Still others compare the engine knocking sound they hear to marbles rolling around inside a coffee can.

The spontaneous ignition of air/fuel inside the cylinders is a common source of engine knock.

While the description of the sound may differ, the circumstances under which it occurs are often the same – low-speed, high-torque conditions common when you’re accelerating.

Engine knock typically occurs during low-speed, high-torque conditions, like when you’re accelerating.

How engine knock occurs

Say the clock has struck 5:00 and you make a bee-line to your truck and take off for home. When you mash the accelerator out of the parking lot, that’s when you hear an engine knocking sound. Or ping. When you let off the gas, it goes away.

This is likely due to either pre-ignition or detonation. They’re effectively the same phenomenon, but they occur at different times.

In a properly running engine, spark-triggered ignition typically occurs a few degrees before the piston reaches top dead center (TDC). This careful timing ensures the downward force of the exploding fuel/air mixture works in tandem with downward piston momentum, resulting in optimum efficiency and power.

That’s bad timing

Pre-ignition (and its cousin, low-speed pre-ignition [LSPI]) are abnormal combustion events that throw off this precise balance. Under certain conditions, the fuel/air can spontaneously ignite too early in the combustion cycle. Sometimes low-octane fuel is to blame; sometimes it’s deposits on the piston crown.

Fuel with too low an octane rating for your engine can sporadically ignite prior to the piston reaching TDC.

Or, chunks of carbon can heat up and create a hot spot that effectively ignites the fuel/air before the plug fires. Then, when the plug does fire a fraction of a second later, the two flame fronts collide. In certain conditions, they can clash with the upward-moving piston. The resulting shock wave rattles the piston inside the cylinder, creating the knock, ping or can-of-marbles sound you hear.

Detonation has the same effect, except it occurs after the plug fires.

Computers in modern vehicles can detect engine knock and compensate by adjusting engine timing. Though it saves your engine from destroying itself, performance and fuel economy can suffer.

Tick, tick, tick

Say your engine is ticking like a time bomb, especially in the morning when it’s cold. You likely have a valve-train issue.

Your engine uses intake valves to feed clean air into the cylinders and exhaust valves to kick spent combustion gases out. The valves open and close thousands of time per minute in a choreographed whirlwind of activity.

top dead center valve timing

A finely balanced system of parts – rocker arms, valve stems, cam lobes, lifters – control their movements. The clearances between these parts, known as lash, can become loose (or sloppy, in automobile nomenclature). When that happens, all those moving parts clattering against each other can create a ticking sound.

It’s especially noticeable in the morning before the oil has had a chance to circulate throughout the upper end of the engine.

Many engines use hydraulic lifters, which use an oil-pressure-assisted plunger and spring to compensate for lash, helping ensure the system runs smoothly and quietly.

Proper oil pressure plays a big role in valve-train operation and noise. Low oil pressure can reduce the effectiveness of hydraulic lifters, increasing lash. This is most likely to occur with a low-quality conventional oil that thins at high temperatures, preventing the engine from developing good oil pressure.

If the rods are knockin’…

Rod knock is yet another possible explanation for your engine knocking sound.

Your engine is built with a designed clearance between the crankshaft journals and the connecting rods. In a properly running engine using a good oil, the motor oil fills those clearances and prevents metal-to-metal contact.

But, let’s say you’ve been using a poor-quality conventional oil.

At high temperatures, the oil thins and the fluid film weakens. The pressure between the crank journals and connecting rods squeezes the oil from the clearances. Now, metal is riding on metal, wearing the surfaces and widening the clearances. Eventually the clearances widen so much that you begin to hear the metal surfaces clattering against each other. Eventually, they’ll weld together and destroy the engine.

Quieting a noisy engine

This all sounds dire. But you can sometimes address pre-ignition by using a higher octane gas or by cleaning deposits from your engine with a fuel-system cleaner like AMSOIL P.i. Performance Improver.

Buy AMSOIL P.i.

Using a higher-quality oil that flows better in cold weather and maintains its viscosity when hot can sometimes quiet a valve-train tick.

Shop AMSOIL Synthetic Motor Oil

Rod knock is the worst of the three. Once the clearances between the crank journals and connecting rods have widened due to wear, it’s just a matter of time before catastrophic damage.

In any case, visit your mechanic and take care of the problem before it gets worse.

The bottom line…

The moral of the story is simply to pay a little more now to maintain your vehicle rather than spend a lot later to fix it.

Use a high-quality oil that stands up to extreme heat and maintains correct oil pressure. Periodically clean combustion chamber deposits with a fuel additive, such as AMSOIL P.i.

Doing so can help keep your vehicle running properly and quietly for years.

Signature Series Motor Oil Protects Engines From Low-Speed Pre-Ignition

SIGNATURE SERIES Protects Engines from Future Industry Problem

LSPI can destroy pistons and connecting rods, bringing an engine to a standstill in seconds. Original equipment manufacturers (OEMs) like General Motors (GM)* have addressed the issue by designing tests to gauge a motor oil’s ability to prevent these destructive events. Signature Series achieved 100 percent protection against LSPI1 in the industry-standard test.

OEMs have been aggressively downsizing engines to meet strict fuel economy and emissions standards while improving power and torque. Most new engines today use some combination of turbochargers, direct-fuel injection and variable valve timing to make more power than their larger counterparts while delivering improved fuel economy.

This scenario seems like all upside for drivers. But today’s smaller, hotter-running engines pose significant challenges to lubricants. The latest is a phenomenon called low-speed pre-ignition (LSPI), also known as “super knock,” which can destroy pistons and connecting rods.

What Is LSPI?

LSPI is another version of engine knock, which has been around since engines were invented. In this case, it occurs under low-speed, high-torque conditions in turbocharged gasoline direct-injected engines – like when you’re taking off from a stoplight. LSPI is the spontaneous ignition of the fuel/air mixture prior to spark-triggered ignition. This form of pre-ignition is more destructive than typical engine knock.

No Magic Bullet

Just as your engine relies on a balanced network of components to function, the motor oil needed to protect it requires additives with the right qualities at the right quantities. While adding more of one ingredient or reducing another seems simple enough, small composition changes can have big impacts. We were determined to find a solution to the LSPI problem without sacrificing the performance of Signature Series in any way.

GM LSPI Test

OEMs like GM have addressed the issue by designing tests to determine a motor oil’s ability to prevent LSPI. The GM LSPI Test records the number of peak pressure events during high-load operation in a turbocharged engine over a five-hour period. Passing the test is required to meet the GM dexos1® Gen 2 specification.

Perfect Score

We armed Signature Series with an advanced detergent system that protects against harmful deposits and LSPI. Signature Series Motor Oil achieved 100 percent protection against LSPI in the engine test required by the GM dexos1 Gen 2 specifications – zero occurrences were recorded throughout five consecutive tests.

API SN PLUS Specifications

API SN PLUS is a recently released specification that was requested by the automobile industry to protect passenger vehicles from LSPI. AMSOIL anticipated this change, and the current formulations of Signature Series, XL and OE synthetic motor oil all meet or exceed the specification. Look for updated product labels featuring the new API “donut” in the near future.

Your customers can be confident that AMSOIL synthetic motor oils protect their modern engines against LSPI, helping their vehicles deliver years of reliable service. For more information on the dangers of LSPI, visit www.amsoil.com/lspi.

 

Example of piston damage due to an LSPI event observed during the testing of a competitor’s motor oil. The red arrows indicate sections of the ring land that have broken away from the piston.

Achieved 100% Protection Against LSPI1

Is There Really an Advantage with Premium Gas?

OCTANE EXPLAINED: DOES PREMIUM, HIGH-OCTANE GAS BOOST PERFORMANCE?

Save yourself a lot of money and use the lowest rating suggested in your owners manual. Typically the only cars which need premium fuel are older high compression engines (pre 1980’s) and the ever popular turbocharged engines. I run premium in my Ford Transit with the Ecoboost Turbo as it is required. The added compression demands it to resiste pre-ignition (reducing knock) and I’ve even verified maximum mileage on Cenex 91 even over the OK’d 89, but on typical fuel injection cars over the past 25 years lower octane ratings are no issue at all  – Enjoy the article below…

Sioux Falls drivers – email me your favorite gas stop you get the best performance from and I’ll make a post listing any feedback we get. Thanks!! Email me at ches@syntheticwarehouse.com

A recent AAA report found that American motorists wasted $2.1 billion in the last year buying premium gasoline for engines designed to run on regular gas.

The reasons why are likely due to the following misconceptions about premium gas:

  • Contains higher energy content (increasing power and fuel economy)
  • Formulated with higher-quality additives (increasing engine cleanliness)

What is Premium Gas?

When motorists see premium 91-octane gas at the pump, they may assume it contains higher energy content compared to regular 87-octane gas. After all, “high-octane” is often synonymous with increased power and performance. The 91-octane gas should, they think, provide improved fuel economy and power.

In fact, octane has nothing to do with energy content or quality – it’s a measurement of the gasoline’s ability to resist engine knock. Higher octane denotes greater knock control.

What is Engine Knock?

Octane neededOn an engine’s intake stroke, the piston travels down the cylinder, allowing air/ fuel to fill the available space. Assume the cylinder holds 900cc when the piston is at bottom dead center. The piston then travels up the cylinder, compressing the fuel/air in preparation for combustion. Assume cylinder volume is reduced to 100cc when the piston is at top dead center. The relationship between the two volumes is known as the compression ratio. In this case, 900:100 is reduced to 9:1. The compression ratio indicates cylinder pressure, and more pressure equals more power and greater efficiency. That’s why high-performance cars and heavy-duty diesels typically have higher compression ratios than standard cars or trucks.

While higher compression seems like all up-side, it can invite negative consequences. Compression heats the fuel/air mixture, allowing it to burn more efficiently. If compressed too much, gasoline can ignite too early, causing uncontrolled and early ignition. This leads to a knocking or pinging sound, robs the engine of power and can lead to engine damage. Typically, the engine’s computer will detect engine knock and adjust timing and the air/ fuel ratio accordingly. Although this protects the engine from damage, it can substantially reduce engine performance and efficiency.

Most high-compression gas engines require use of premium gas to better resist engine knock and prevent the computer from detuning the engine to protect against knock-related damage. Using premium gas in a clean, mechanically sound engine not designed to use it, though, provides no benefit.

In engines with carbon buildup on pistons or in the combustion chamber, however, premium gas can provide some benefit. Deposits can reduce cylinder volume at top dead center, effectively increasing the compression ratio. This alone can lead to engine knock. The deposits can also become hot spots that preignite the mixture, leading to engine knock.

In these cases, a higher octane fuel helps resist engine knock and allows the engine to operate closer to its normal conditions rather than detuning to prevent engine knock.

For best performance, use the fuel recommended in your vehicle owner’s manual.

Higher Octane Doesn’t Mean Higher Quality

The other popular misconception is that premium gas contains a higher concentration of cleaning agents and other performance-improving additives.

While many formulators market a highquality premium gasoline, such as Shell* V-Power* Nitro+ or ExxonMobil* Synergy*, the premium gasoline at your local filling station may not be formulated to improve performance in any aspect other than octane rating. Quality can vary from brand to brand and station to station.

This is why we sell AMSOIL P.i.® (API)  for cars and trucks and AMSOIL Quickshot® (AQS) for smaller engines. They provide excellent detergency to help clean dirty injectors and carburetors for maximum fuel economy and operability. Once you understand the truth about premium gas, these additives will better assist in overall performance thus giving better peace of mind and benefits you’re seeking.