Thread: 3.5lt EFI day to day fuel economy

Went for a day-trip up to a friend's farm, yesterday 404km round trip. (Mundaring to Mundaring, same fuel station)

Took the family flagship, late model Magna 3.5 litre V6. (Lady Sarah is in disgrace.. and the Boss refuses to ride in her .)

Used just under 40 litres of 98, - She reckons HER car prefers the Good Stuff over common old '91'

Overall useage, Cruise Control and relaxed-style driving yielded 9.88 litres per 100km, (10.1253 km/litre / 28.6mpg) despite the on-board computer claiming a mere 9.6 l/100

About $13.50 per 100km.

Sarah would have guzzled 18 to 20 litres per 100km, or $30 per 100km, going on the last time I took her out.

About TWICE as many $s for fuel, and the RR seats are not 'twice as good' as the Magna.

Originally Posted by Konradical

Thanks guys for some really good replies.

I used to have access to a digital ossiloscope at my old job and I could have run some of those tests.

Unfortunately I don't have access to a CO tester, I have asked around town, cause I think getting that right would go a good way towards getting the fuelling right.

But as a running update and over four consecutive fills, the repairs seem to not have made any change, other than smoother acceleration. I'm still getting 19.5 or so litres per 100km.

Il keep at it, testing and tweeking things, until I get to the inevitable point of rebuilding the engine.

Thanks again for the help..

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I've been told by numerous folk here, that the First Step is ... getting the IGN system up to scratch, - better spark and more advance, and etc... - followed by replacing the LUCAS injectors with the (?) FORD 'yellow' ones.
THEN start fiddling with o2 sensors and the like.
More narrow tyres make a difference... You don't need 265 wide for highway use. 205/80 or 225/75 is fine.

IF I decide to keep Sarah for a bit longer, she'll be wearing 205/80 new shoes...

18 to 20 is a bit high, but not too much. 16 to 18 was my average on the highway. The engine and fuel injection system is old school / primitive. Newer engines have sequential injection, not bank, better air flow characteristics, higher compression etc.

Originally Posted by superquag

Went for a day-trip up to a friend's farm, yesterday 404km round trip. (Mundaring to Mundaring, same fuel station)

Took the family flagship, late model Magna 3.5 litre V6. (Lady Sarah is in disgrace.. and the Boss refuses to ride in her .)

Used just under 40 litres of 98, - She reckons HER car prefers the Good Stuff over common old '91'

Overall useage, Cruise Control and relaxed-style driving yielded 9.88 litres per 100km, (10.1253 km/litre / 28.6mpg) despite the on-board computer claiming a mere 9.6 l/100

About $13.50 per 100km.

Sarah would have guzzled 18 to 20 litres per 100km, or $30 per 100km, going on the last time I took her out.

About TWICE as many $s for fuel, and the RR seats are not 'twice as good' as the Magna.

My POS on gas will get 250 k's out of 58 litres of lpg on a trip, 220 dagging around.

That's about 0.23 litres per km on a trip or 23l per 100kms on a trip.

At 47.3 cpl that's about $10.90 per 100km.

If I recoed the motor and rejigged the ignition I think I'd get 5km per litre, but it doesn't stack up atm.

Correct my maths if I'm delusional please!

cheers, DL

350RRC, the 3.5 1989 Classic we used to tow a two-tonne sweeper and trailer, gave barely 3km/litre on LPG, and 4km/litre on petrol. Cam had been changed for 'towing' by the PO. LPG was often around 2 km/litre IF the owner was driving !

I think many 'new' to LR owners could almost be forgiven for asking this somewhat repetitive question: "Why is my fuel economy so s***???"

To which most of us now seasoned to the drain quip to ourselves while typing responses "did you do any ****** research before you bought it?"

It's widely accepted that rover v8 is not very fuel savvy in a LR product - but what are the real reasons?

Well, the answer to the question isn't so straightforward. Because the already barely average fuel economy of a v8 rangie, disco, or county can be affected quite considerably just through lack of maintenance, poor choice of fuel, and degrading electricals. Add Tyre variations, driving style, terrain and usage, and there are way too many variables to make sense of.

So let's try and add a few of the basics.

Let's assume that the person who asks this question in the future, is wholly new to LR and knows nothing other than what has been read on various internet fora, and youtube videos.

Start with fluids...

Before any real diagnosis takes place, baseline measurements and data should be recorded.
So, in order to do this, you commence your maintenance handbook with a service.
Note the date, odo reading, and any anecdotal evidence if you are performing a task which leads you beyond 'weights & measures'

1. full tank of fresh fuel - at least 95RON. Note the litres and cost if you want to keep economy data for future reference. Pump your tyres up to the correct operating pressure. on-road, that is around about 32-38 psi, depending on your load and the climate. If you drive on dirt, then adjust your pressures accordingly for the road surface.

2. Ensure the vehicle has satisfactory operating fluids.
This means checking the levels of engine, transmission/gearbox, transfer case, diffs and swivels, coolant, brake fluid and washer bottle.
Note the levels, and if possible start your baseline now, with a full flush of every fluid with new.
Replace the filters; fuel, oil and if you are suitably confident, the auto trans filter, if your vehicle is automatic.
Recycle your dirty fluids. do not dispose of them down stormwater or sewer.

3. Lubricate all necessary moving surfaces - bearings, universal joints and slipjoints.

4. clean your AFM / MAF if you have an EFI vehicle, clean the throttle body also, with an upper engine cleaner, or appropriate aerosol for the MAF (CO Cleaner) Same applies for carburettors, some carbi clean and if possible clean the needle & seat, check the float level is correctly set and the float is serviceable. If not run a kit through the carb.

Ensure any vacuum tubing is not leaking and correctly plumbed.

ensure the disctributor cap, rotor, leads and plugs are either replaced with new or are serviceable.

Make sure the battery voltage is adequate, both unloaded and under starting load.

That pretty much takes care of the pre-work. Once this is completed, the baseline for your fuel economy is completed.

Drive your car as you would normally. Don't do any 'extra' runs, just use it as a normal vehicle, and when you have to fill up your tank, log the mileage and the litres / cost in your log book.

reset your trip meter and perform the same procedure for another tank. Lather, rinse, repeat.

After 3-5 tanks of fuel, you now have a basic dataset to commence working with.

At this point, You can check the wheel alignment, the ignition advance and dwell, the fuel pressure at the fuel rail (on efi v8's) or the obligatory carb diagnostics.

check all operating fluids are correct level. if you need to adjust any, note the amount and the mileage on the odometer - this will become important later.

Follow the Range Rover service schedule. The US RR forum has an extensively detailed PDF of the maintenance schedule... in my opinion it is probably just one step removed from an OCD behavioural diagnosis, but - it is useful.

Now that you have baseline data, you can make adjustments.... start with setting the static timing to around 12 deg btdc. The engine can possibly take more, but 12 is a good place to start.
Also at this adjunct, I recommend a thorough reading of the Bee-Utey distributor modification thread - aka dizzy module BIM024 remote relocation. If you are OK with the tools, jump into this as soon as you have the means.

A couple of other useful areas to check, are the 'flame trap' breather and hose, the Idle air control, and the intake plenum - both for correct tightening and leaks around the gaskets and plenum itself. Correct any deficiency and note it in the log book.

By now, I'm hoping you can see a pattern in this little 'rant'. The idea is to create an accurate dataset, which can be relied upon for any future maintenance or mechanical needs, and not just to monitor whether any changes made have a direct affect on the fuel economy of the vehicle.

The reality is, there are many variables - too many - to make a broad sweeping statement about why you are getting the fuel economy figures that you're seeing, versus other people's vehicles.

It's not 'driving style' or simply 'fuel' or trip type that have an effect. Vehicle loading, age, engine health, even the lubricants and mechanical components used in the vehicles maintenance have an impact on the fuel consumption.


So, the real answer is.... "To compare figures is folly".

What you can do however, is follow the process I have mentioned and take rigorous notes at every service interval, every fuel fill, log the litres and cost and distance travelled.

At worst, you will have an excellent vehicle maintenance record. At best, you will be able to decipher what changes to the vehicle have had a direct impact on the fuel consumption of the vehicle - and the longer you do this for, the more accurate the data will be. Especially when people talk about city/highway/average consumption figures.


I realize I have left things out and have only scratched the surface on this topic, but as someone who has always been keen to keep track of cause and effect when making vehicle moifications or maintenance, I have found it to be quite invaluable, and also dispelling any misbelief I may have had with just straight up factual data.

You can't ask for much more than that, because every vehicle and every driver are different.

The low compression motors are worse, to get any where near some kind of efficiency the CR has to be bumped up to the max that normal ULP will handle.
My old 85 Rangie had a fresh hi comp 3.5 when i bought it and although it was never going to get good figures with a TF727 behind it, it was nearly as good as my older 81 with 3.5 LC that had ported heads, scorcher dizzy and a holley 350 - this gave me a respectable 22mpg on 215/80/16's.

Mercguy

Pretty much what you have put down is what I have been doing over the last few months. But with a twist.

Due to a poor time currency, I will check/adjust/repair something and run three full tanks of fuel to see how much, if any, of a difference has been made.

So far I have replaced a bunch of vacuum hoses, cleaned the plenum chamber, replaced all wheel bearings and swival pin housings, replaced diff oil, replaced the vacuum advance unit, adjusted timing to 10 BTDC, New 74 degree thermostat, New ECU temp sender, two fuel filters(keep blocking, changed fuel source now), keep on top of tyre pressures(38 front and 40-42 rear), 140 amp alternator, New coil and leads, removed roof rack and folded back light Bar.

So far doing all that has changed my 19.5-21l/100 to a steady 19.5l/100 and runs smoother and improved acceleration(improved, nothing to get excited about). This has been using 95ron Shell fuel. The same fuel and pump I have been using since Jan 15 when we got to Katherine.

Now after the second blocked fuel filter since the beginning of June, I have decided to use another supplier and by chance they had 98ron. The reason that is exciting is because they rarely if ever have it AND they are the only place in town to get it. Now it's probably very premature, but I am currently up to 126km at a quarter of a tank. Usually it's been about 75-85km at the same point. I am now going to try and fill up weekly as opposed to whenever I need it.

Over the coming weeks, the girl will be due for a service, so I will complete a oil change, Trans oil change and if I get the time, replace the unijoints.

Now please don't get me wrong, I never got into this vehicle expecting glory, I was very aware that something this big with a small engine was going to be thirsty, the reason for the thread was to find some possible explanations as to why my fuel usage went from 475kms per tank to 330kms per tank without changing its configuration.

A lot of the feedback has been awesome and useful.

I do hope that without doing a engine rebuild, I can restore some of the old economy.

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