Is premium gas really necessary on engines with knock sensors?

IHAVE A 03 jaguar stype my DYNAMIC STABILITY CONTROL LIGHT IS ON.Can anyone tell me what to do to fix it thank you. Carl

IHAVE A 03 jaguar stype my DYNAMIC STABILITY CONTROL LIGHT IS ON.Can anyone tell me what to do to fix it. thankyou Carl

Michael is correct.

JAM, your remarks broadly apply to many cars, but not all. Many cars DO require premium fuel and the mnaufacturers specify it, regardless of what pro-consumer organizations say.

Take, for instance, my XJR: using regular will result in knocking. As Michael said, the knock sensors "hear" the sound and the ECU dutifully retards the timing, resulting in a loss of power and fuel economy.

Wayne, what is your definition of "late model Jag", specifically?

Doug Dwyer
Longview Washington USA
1995 XJR

It used to be an easier question. Before modern electronic fuel injection, you could use any gas that didn't make the car knock. Using this test avoided broad brush generalities. Your car could either use regular or not, and you knew it, because the engine would complain if it wasn't happy. XK motors are more knock prone than other engines because of the high domed pistons, and I suspect that most 9:1 XK engines would fare better with premium.

With a modern engine it's much more complicated. The reason is that modern electronics can alter engine timing, injector bandwidth, and in some cases, cam timing. So even the most exotic car can "adjust" to running on low octane fuel. What this means is that the timing is dynamically retarded and the intake/injection process detuned to match the gas. Your engine won't audibly knock under any circumstances. The ECU will sense the first sign of knock, and make adjustments accordingly.

As a result, the answer for a modern car is that if the car maker recommends premium, that's what you use. If you want to drive around thinking that you've saved a buck because your engine doesn't knock on regular, it's only you who's being fooled. You will use more gas, your engine will wear, and your exhaust will run hotter. And perhaps your check engine light will come on. Last but not least, you may be voiding your warranty.

Of course, if the manufacturer recommends regular, there's no point in switching to premium fuel. ECU's can detune an engine when they sense knock, but can't "uptune" when the fuel is less knock prone than expected. If you use premium in a car designed for regular, nothing special happens. In this case, you'd be wasting money.

For whatever it's worth - when I still owned my '90 XJ6 Sovereign (which indicated that I should use Premium fuel only) if I dared put in anything less than remium the check engine light would come on until I used at least half tank of gas and could refill with Premium.

May not have been important one way or the other but it seemed that Maude could tell the difference.

KLW - Mt. Vernon/Alexandria
Westminster Blue 1989 XJS

Art Dickenson.
1983 XJS GT "Silver"
Pacific Jaguar.ca

When I was back in England in my youth,I read a book on the subject of tuning by Phil Irving. Phil believed that anything with a compression above 8.5 to 1 needed high octane fuel. With the older Jags having hemi pistons, I believe they have a greater need for high octane, I have seen pistons that have been damaged with probable usage of cheap gas.
Most of the newer vehicles state on the fuel cap / door the fuel requirements, e.g my sons 2002 X Type states "Premium Unleaded Fuel only".
There are however many North American vehicles with high performance that only require 87 octane, Jaguars I believe need higher than 87 but perhaps a higher mid grade can be used if maximum acceleration is not required, although mileage may suffer slightly.

I conclude the answer is NO, you DO NOT have to use premium gas in your late model Jag, not even in a 1965 3.8 Jaguar engine with 9:1 compression.

I think that if ANY car company made any car that required the exclusive use of premium gas, and consumers were not warned about it in order to make an informed decision, the manufacturer would have a class-action lawsuit bigger than the Weapons Of Mass Destruction concoction we've all been led to believe.

If weu spend some time reading studies and experiments done by Consumer Reports and other mostly-reliable pro-consumer groups, the conclusion is also NO for any car. If you read the "statistical writings" done by corporate groups who obviously have an agenda behind their so-called "conclusions", then you will be scared into buying the so-called "Premium" gas.

But I always say, it's your money, you spend it as you please.

The main difference between Man and Ape is mans ability to think freely. I'm glad to see someone is utilizing that difference. Jaguar affectionado and etc.