one more fuel grade inquery
 

Alright so obviously different pumps have different grades and not all pumps share the exact 3 grades (at least not around here). To date every since I replaced my rear driveshaft I've been using super premium fuel. Is this the recommended grade or? Or is it "premium".

That's a good question. I also have a D1, a 1998 with the 4.0 and I do not believe it has a knock sensor. Therefore my best guess is that with this engine, the lowest grade fuel that does not cause pinging can be used. More sophisticated engines will retard the timing when knocking is sensed and power and efficiency will suffer but the engine will have some protection. In the case of this 4.0, again if I'm not mistaken (this engine is new to me), we would need to watch out for pinging or be safe and use a fuel with more than sufficient octane. I'm hoping that by making ignorant statements, someone will oblige me with knowledge.

I'm only on my second tank. I'm using 91 until I figure it out. I'm busy with other stuff but it's on my list.

you are good to go with 91+. I always put 91+ unless im in the middle of nowhere and i know the 91 has been sitting for months if not years, then i will put 87 just because bad gas is worse than low octane gas.

I'm betting the '03 and '04 4.6L V8's have knock sensors and improved exhaust valves and will run any fuel safely, but for my '98 4.0, I'm the sensor for knocking, pinging and sticking exhaust valves.

The GEMS and the BOSCH engines have knock sensors.

Land Rover - Parts, Accessories and Information

Been running 89 octane for almost a year now. Runs the best with that octane vs any other grade including 93

But this gas station only has 89 so I know it always has that grade

good way to kill it. it's like smoking cigarettes. won't kill you instantly but slowly turns you black from the inside out.

My spark plugs tell otherwise...best way to tell what your engine is doing

Also my mpg goes down with 91

MPG all depends on the amount of ethanol in the fuel, the more ethanol the lower the MPG.

All electronic ignition engines have knock sensors.
All dizzy's have a vacuum advance which was a old school way of adjusting ignition timing for the load on the engine.
Knock sensors do that now, they do not "compensate" for the grade of fuel, they adjust the ignition timing based on engine load to prevent spark knock.
Using the wrong grade of fuel in your Rover will do nothing in the short term, but in the long term your engine will self destruct.