I'm assuming that our Discos need premium fuel because the ignition timing has been advanced as far as possible to eek every possible bit of power from these engines. Generally, engines tuned like this will exhibit pre-ignition (knock) if run on regular/low octane fuels.

I know that in most cases, electronic engine management systems make it impossible to change ignition timing, but thought I would ask the question.

I would be happy with a little less power and to be able to same 30-50 cents on every gallon of fuel.

Many modern cars have knock sensors that allow a car tuned for premium gas to run with retarded ignition on lesser octane fuels. When I worked at BMW in the mid 2000s, all new cars went out the door with regular low octane fuel,....ran fine,....however, with premium fuel, there was an improvement in performance, (because the knock sensor would hear nothing and advance the ignition timing) and some said fuel economy improved as well.

Brian in Austin

 

There is a big debate to see if using the lower octane gas makes that much difference. I have a 2003 SE with 120k miles on it and use a 180 thermostat and always use the lower octane. I have not seen any difference in either engine performance or gas milage. My $0.02

 

In theory, a vehicle that spcifies premium fuel like our Discos, will pre-ignite or "PING" under moderate to heavy acceleration with lower octane fuels.

Higher octane fuel control or slow the wave-front of the burning fuel/air mix, so that it does not happen pre-maturally.

If we could retard our ignition a few degrees, then I believe we could use lower/lowest octane fuels without the risk of Pre-ignition/detonation/Pinging.

Are you running mid-grade or regular/lowest octane?

Brian

 

Well, the ECU monitors the sensors, including the knock sensors, and adjusts the spark timing on the fly constantly. Per cylinder. Pretty smart little hard working box. So while it could be changed to optimize for regular, would require more than a snip of a jumper in a D2.

Because it is so smart at what it does you won't notice much difference when driving in average conditions. Towing a trailer up the mountain I'll let others comment, I live on the coastal plain where it is flat. Gas is down to 2.93 a gallon locally for regular.

Don't believe the $69 chip ads, even though some appear on this forum (along with Jeep ads) - if it really worked we'd all have them by now.

Varying gas quality in Europe is common, before the smarter ignition systems Mercedes had a little **** on the dash that let you select several timings to compensate for the gas quality. Bosch has automated all that.

In earlier D1s there is some change that can be done with a resistor in the ECU, from the RAVE:

Tune select resistor -
To suit individual market requirements a tune select
resistor is connected across pins 5 and 27 of the
ECM.
It is located adjacent to the ECM, and strapped to the
MFI cable assembly. The value of the resistor is
dependent on the market application:
Red wire, 180 ohms, Australia, Rest of world.
Green wire, 470 Ohms, UK and Europe - non catalyst.
Yellow wire 910 Ohms, Saudi non catalyst.
White wire, 3K9 Ohms, European catalyst

On the D2 it is a program step that can be changed with shop level computer: (from RAVE)

The ECM is available in 4 variants:
l NAS.
l NAS low emission vehicles.
l UK/ Europe/ Japan/ Australia.
l ROW/ Gulf.
The ECM uses a 'flash' electronic erasable programmable read only memory (EEPROM). This enables the ECM to
be externally configured, to ensure that the ECM can be updated with any new information, this also allows the ECM
to be configured with market specific data. TestBook must be used to configure replacement ECM's. The ECM can
be reprogrammed, using TestBook/T4, with new engine tunes up to 16 times to meet changing specifications and
legislation. The current engine tune data can be accessed and read using TestBook/T4

The US 4.0 engines were available in two compression ratios, the low one for certain emission levels in certain states (8.23 and 9.35). I think a lot of the tune select is based on catalysts and gov't smog rules in various places.

There is one fuel mod that was sent out in a TSB for all Rovers....

 

I use my disco for both a daily driver and for heavy off roading as well and I always use EL Chepo Mucho gas. I also tow a heavy loaded trailer either up to VT or Down to FL a couple of times a years as well. When not towing then i get 18.2 mpg. Calculated both through Ultra Gauge and pencil and paper. Every 6 months I will push a can of sea form in the gas tank but not notcied any difference. Even when changing the spark plugs have seen no difference in them either.

 

I guess I must be the exception but I believe my Disco is actually a very sophisticated gasoline analysis tool.

It knows when I buy cheap gas and it even knows when I pay full price for premium and get either something else or just old fuel.

I ALWAYS run Chevron Supreme with the exception of when I can find supreme with no ethanol and then I buy that.

If I get cheap or old gas engine performance changes noticeable. I see no difference that I can tell on the Ultra Gauge but I can hear and feel the difference in how my engine runs.

Possibly this is a feature of the 4.6 as many of you who don't notice seem to be driving 4.0's.

I thought this may change with the HG job, newly cleaned and polished heads, BG ran through the intake and injector bank soaked in it too...

With a spotlessly clean top end I can still tell if I get a tank of lesser fuel.

The other possibility is that if you run enough cheap fuel you don't really know what it suppose to run like and just assume yours is normal.

 

re: if you run enough cheap fuel you don't really know what it suppose to run like and just assume yours is normal

probably right on the money.

 

I would be happy with a little less power and to be able to same 30-50 cents on every gallon of fuel.

Brian in Austin: "Many modern cars have knock sensors that allow a car tuned for premium gas to run with retarded ignition on lesser octane fuels. When I worked at BMW in the mid 2000s, all new cars went out the door with regular low octane fuel,....ran fine,....however, with premium fuel, there was an improvement in performance, (because the knock sensor would hear nothing and advance the ignition timing) and some said fuel economy improved as well."

For my 2004, 4.7 L. engine, I think that the above is what is happening, at least to some degree, because when I first started using the cheap low grade, low octane but expensive gasoline, $3.60 something per gallon, I got some pinging whenever I hit accelerator hard, which worried me BUT, it soon corrected itself, and stopped doing that, stopped the pinging. Now, after continuing to use the same low octane gas, I no longer hear any pinging at all. However, I never tow anything, and don't climb up any steep mountains, nor do I do jackrabbit starts---if I did, I would probably put in some higher octane fuel first. As of now, I have seen no ill effects from my using the cheap gas. On my earlier Rover, a 1991 Range Rover classic, with same engine in 3.9 L. capacity, I rebuilt that engine, installing lower compression Rover pistons (so I could burn cheapest gas, with no ill effects), and I did exactly that, over the next 150,000 miles. Some guys swear that we must, for sure, without failure, use the most expensive highest octane fuel we can find for our Rovers, giving all kinds of horror stories of what will happen if we don't. Well, my stock 4.6 L. does not ping under my driving conditions thus far, and I have yet to see a single one of those horror stories come true. Time will tell if they know something I don't, or if they are just spreading unprovable myths based on conjecture.

 

I don't know about anyone else but I figure I own a premium vehicle. I'm not about to start using the cheapest possible parts or fuel.

If you want cheap, just buy yourself a used Suzuki Samurai.

 

is it just for me or does early rover's post show "blue=color important!" multiple times?
makes thing hard to read, for an idiot, like me.