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Cost is often the first thing that comes to mind when motorists think of gasoline. Many will drive halfway across town to save a couple cents per gallon. Additionally, purchasing regular-grade fuel to save money can be an exercise in false economy, especially if your vehicle is designed for premium gas.
Running fuel with insufficient octane can cause internal engine damage, which isn’t pretty. “The worst case scenario …. You could actually [melt] holes in the pistons and cause catastrophic damage to the [connecting] rods,” said Bill Studzinski, GM powertrain fuels group manager. Fortunately a disaster of this caliber is unlikely in today’s highly tuned, computer-controlled powerplants. Still he said, “You should follow the owner’s manual guidance.”
What’s more apt to happen when there isn’t enough octane is a phenomenon called spark knock. John Juriga, director of powertrain at the Hyundai America Technical Center described this abnormal combustion as “sort of a high-pitched pinging,” or perhaps even a rattling noise. This sound is caused by colliding flame fronts inside the combustion chamber, which lead to pressure spikes and ultimately that telltale sound. “Obviously knocking is not something customers like to hear,” he said, nor is it good for your engine.
Octane is a measure of gasoline’s resistance to igniting under pressure. To improve fuel economy and output figures, manufacturers often increase the compression ratios of their engines, that is, how tightly they squeeze an incoming air-fuel mixture. A lower-octane fuel is more likely to spontaneously ignite than one with a higher rating. For these reasons and more, performance vehicles or ones equipped with forced induction often demand premium.
Studzinski said GM has two different fuel requirements. In some of their cars and trucks high-octane gasoline is recommended, in others it’s mandatory. Of course many of their vehicles are designed to happily burn regular gas.
It’s same story at Hyundai. Juriga said all of their products are rated to run on 87-octane fuel, though the Genesis models and Equus luxury sedan will benefit from premium, delivering more power and torque.
These cars are able to adapt to various octane levels. Juriga noted that they’ve allowed “the engine to sort of regulate itself.” Knock sensors detect any pinging and tell the powertrain-control computer to dial back spark timing to eliminate it.
Juriga said more advanced ignition timing – having the spark plug fire earlier – improves both low-end torque and high-RPM power, which is why automakers try to push it forward, though there is a practical limit.
Curiously, high-octane gasoline isn’t always the same from one market to another. “The petroleum industry has decided to sell premium as two different grades,” said Studzinski. East of the Mississippi River it’s rated 93 octane, west merely 91. Fortunately either should work.
“For General Motors in 2015, and previously, we always defined premium as 91 AKI or higher,” noted Studzinski. That three-letter initialism stands for anti-knock index, which is “the posted octane on the pump.”
What if you drive a vehicle that recommends premium fuel and you decide to save a few bucks and fill the tank with regular-grade gas? Studzinski said, “You won’t damage your engine but the following are the side effects: acceleration will be poor … and [a] loss of fuel economy.” This could be an instance of being penny wise and pound foolish.
Conversely if your car is only designed for 87 octane buying the
Without a doubt, every owner dreads the moment when their car won’t start. What should you do? Who should you call? Can you fix it yourself? Here’s a list with ten common reasons why cars don’t start up and what you can do about it.
'The first step is to define the no start' said Joe Spadafora, certified instructor at Universal Technical Institute’s Exton, Pennsylvania campus. Spadafora spent the majority of his career in working in the service department of several dealerships and receiving factory training from GM. He’s certified as a Master Technician and certified by Chrysler as a Dodge Viper technician . He also holds certifications from Subaru, Suzuki, Toyota, Lexus and Scion as well, so if there’s something wrong with your car, chances are he’s seen it before.
To diagnose the reason your car isn’t starting, you need to pay attention to happening when you turn the key. 'Does the engine crank but not actually start or, when you turn the key, does literally nothing happen?' he said. 'In a customer’s eyes, the following two options are the same because both create a scenario that results in the vehicle’s failure to run.'
While the two situations might seem similar, they have very different meanings that are important to a mechanic and can signal different problems calling for a variety of solutions.
'It’s important to note that a vehicle is an extremely complicated machine and can exhibit similar symptoms for a variety of reasons,' he said. 'That is why it’s important to first look at the type of ‘no start’ and then at the list of conditions that could be causing it in the first place.'
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