Low-Speed Pre-Ignition and What to Do About It
Around 2012, turbocharged high-performance 4-cylinder engines like those in the Ford Focus ST and Mazdaspeed3 came onto the market, squeezing horsepower out of small displacements while saving fuel. These engines outperformed their naturally aspirated counterparts.
But these engines had an unexpected failure, called low-speed pre-ignition (LSPI), that caused mysterious problems in high-speed cars.
- What is LSPI, and how did it cause problems for these interesting performance cars?
- What can be done about it?
- What is pre-ignition?
- For decades, manufacturers have designed gasoline engines around the risk of pre-ignition. Most gasoline-powered piston engines can suffer from this problem, and manufacturers have found ways to manage it successfully.
Pre-ignition occurs during the piston’s compression stroke, a few microseconds before the mixture is ignited by the spark plug. The temperature rise of the mixture during compression and hot spots in the combustion chamber cause this phenomenon.
Pre-ignition causes a loss of power, and if this occurs over long distances, the top of the piston can burn. Generally, this problem is mitigated by using higher quality (higher octane) fuel.
Low Speed Pre-Ignition
Compared to traditional pre-ignition, low speed pre-ignition (LSPI) is a monster. It is sometimes called stochastic pre-ignition (SPI). This phenomenon was discovered early in the history of the T-GDI engines mentioned above and started to rear its ugly head.
Cars were being returned to dealerships with cracked and broken pistons and bent piston rods. What was going on there? The manufacturer’s engineers got involved and discovered the following:
1. A very high energy pre-ignition event was occurring during the piston compression stroke, well before the intended fuel air ignition. When this happens, the piston is driven upwards by its three comrades and is unable to reverse direction.
2. The extreme pressure caused by this sudden event usually cracks or breaks the top end of the piston and may even bend the connecting rod. Severely affected engines will rattle to a halt and often require an overhaul.
Causes of Pre-Ignition at Low Speeds
After automotive engineers gained experience with conventional spark advance, the cause of these deleterious LSPI events was initially a mystery. Serious engine testing and analysis began. Manufacturers met with fuel and oil producers to jointly address the issue. They discovered the following:
1. During the piston’s compression stroke, tiny droplets of residual fuel and oil were squeezed out around the top of the piston. This mixture was heated by the compression and ignited. Directly injected fuel would also come in at about the same time, igniting and trying to push the piston backwards, potentially causing the damage mentioned above.
2. LSPI was simply a more harmful pre-ignition event that occurred especially in small displacement turbocharged direct injection engines. The cause of LSPI is still not fully understood, but tests have shown that improved engine lubricant formulations may be able to mitigate the problem. These improved oils soon started appearing on the shelves of your favorite auto parts stores and big box stores.
Lubricant Blends That Minimize LSPI
Whether you do your own oil change or have a repair shop, dealer, or local oil change franchise do it for you, you need to learn the technical specifications of the type of oil used in your car’s engine.
This is not a complicated learning process, and because of the higher risk of LSPI in small T-GDI engines, this knowledge proves to be very important if you drive one of these vehicles.
Many brands of motor oil can be upgraded to reduce the risk of LSPI. These upgrades are evidenced by the specification data printed on the oil containers on the parts store shelves. What to look out for?
On the back label of your favorite oil brand, you will usually see a circular code called a “donut.” In the center of this donut, you will see the oil’s viscosity grade: B. 10W-30. It will also show the oil’s API (American Petroleum Institute) specification: B. API Service SN.
You might also see the oil grade in bold. For example: “Meets or exceeds API SP, SN PLUS, SN, SM requirements”.
You may also find specific car manufacturer specifications, such as “Chrysler MS12633”, or specific vehicle models, such as “Nissan GT-R”. Additional specification designations, such as “ILSAC GF-5” or “GF-6”, may also exist.
So what oil specifications are suitable for small displacement turbo gasoline engines? Here is a list. The oil you use must meet one or more of the following specifications:
– API Service SN Plus or API Service SP
– ILSAC-GF6 or -GF6A
– Jim Dexos 1 Generation 2
Check your user manual
Some or all of the above specifications can be found on a container of oil suitable for T-GDI (Turbocharged Gasoline Direct Injection) engines. If your car is a 2019 model or older, your owner’s manual may not reflect these new specifications.
However, you should use these new oils. They are blended to be backwards compatible with the oil requirements of vehicles with older T-GDI engines.
European and Japanese cars may have different approved lubricant specifications. If you own one of these T-GDI vehicles, contact your dealer’s service department. They will recommend a current engine oil (or oil specifications) that are specifically updated to minimize the risk of LSPI.
Finally, when you take your car to a local repair shop or dealer for an oil change, be proactive. Find out the oil specifications for your car and ask the service manager if they use an oil that meets your car’s needs. If not, you’ll need to find a new workshop to get your oil changed.
