Improving fuel consumption - 95 Series V6 petrol 3.4

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

As far as the 98 v 91 octane is concerned - I will test 98 once the current city cycle is complete. My own experience with 98 octane fuel is that - in motorcycles at least - even without a knock-sensor, the response from the motor is improved. Older bikes where the compression ratio has been lifted, also benefit from the use of 98 octane. I know that the Prado does not run high-compresion - but if the ECU does have the ability to detect knock - and can advance the timing to suit - then technically at least, the use of 98 octane should result in slightly better economy and increased power. By how much ? Is the million dollar question. I am confused though about these posts from Crooza - it can be one or the other - but how can it be both ??

Yes the timing is controlled by the ECU so as revs rise and fall the timing is advanced or retarded (for which the knock sensors play a part), but it does not have/can not by any means of anything on the vehicle, detect the octane rating of the fuel used, so it can not increase fuel econ or power of the motor.
What people are feeling is increasing the power of the motor is most likely fresh fuel, as fuel ages the quality drops as does power and econ.

The technology at the time the 5VZ came out was not startling compared to todays standards. The same goes for diesels, look at what they were like back in 1995 (when the 5VZ first surfaced) to what they are now. The problem with most people is they try to compare the tech from then to what is out now, you wouldn't do it with a computer, why do it with the electrics of the motor.

[Torrie 72 Senior Member Find all posts View Profile Close Torrie 72]

Yes the timing is controlled by the ECU so as revs rise and fall the timing is advanced or retarded (for which the knock sensors play a part), but it does not have/can not by any means of anything on the vehicle, detect the octane rating of the fuel used, so it can not increase fuel econ or power of the motor.
What people are feeling is increasing the power of the motor is most likely fresh fuel, as fuel ages the quality drops as does power and econ.

The technology at the time the 5VZ came out was not startling compared to todays standards. The same goes for diesels, look at what they were like back in 1995 (when the 5VZ first surfaced) to what they are now. The problem with most people is they try to compare the tech from then to what is out now, you wouldn't do it with a computer, why do it with the electrics of the motor.

So if the timing is being advanced and retarded then higher octane fuel will allow more advanced timing without knocking which in turn will produce more power.

Cheers, Ben.

[Leethal Advanced Member Find all posts View Profile Close Leethal]

So if the timing is being advanced and retarded then higher octane fuel will allow more advanced timing without knocking which in turn will produce more power.

Cheers, Ben.

Agree totally

Lee

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

So if the timing is being advanced and retarded then higher octane fuel will allow more advanced timing without knocking which in turn will produce more power.

Cheers, Ben.

Timing is only advanced or retarded due to revs, it has nothing to do with anything else. The ECU CAN NOT advance or retard the timing with what fuel octane your using.

[Gosling1 Junior Member Find all posts View Profile Close Gosling1]

I booked in the cook's new Yaris for its 12 months service yesterday, at the same local dealership where my Prado was recently serviced......sorry long post coming up

While I was in the office getting the paperwork sorted out, one of the mechanics came in to speak to the guy doing the booking. Turns out that this mechanic was actually the workshop foreman, who has worked in that particular dealership workshop for about 15 years........and he was the guy who did the service on my Prado. Nice........he asked if I had noticed any difference with the work that had been done. When I told him that the mileage had improved from 15.5l / 100km on the highway to 12.5l / 100km, he said that was a good improvement, and I should also notice an improvement in the city cycle as well.

It seemed like a great opportunity to run some of the issues raised here - about the transmission, the benefits of 98 v 91 and the ECU capabiliites - past him for comment. It was 5pm anyway so he was about to knock off ......

This is what he advised:

* The 4-speed auto will select 4th gear regardless of what the temperature gauge reads. This advice is consistent with how our Prado has operated since 2003. The only thing that drivers may notice when the engine is cold, is that the gearbox will hold 3rd gear for a little longer than usual - this is to help the trans fluid get up to operating temperature. But the gearbox will not hold in 3rd if you have overdrive selected and the engine is still cold. If it does - then that is the sign of a faulty transmission which will need to be inspected.

* The ECU sensors operate immediately. They don't need 5000 or 6000 km in order for the ECU to advance the timing. It occurs instantly. This advice is consistent with every other ECU I have had experience with....(mainly bikes - but fuel injection is fuel injection....). The mechanic said that the ECU in the 95 Series was pretty advanced for its time......

* The ECU cannot directly detect the octane level of the fuel being used, as their are no sensors which detect actual octane level. The knock sensors however - do detect when knocking occurs and send a signal to the ECU. The ECU does advance and retard the ignition timing, depending on the signals being received from the knock sensors. Using 91 octane fuel the ignition advance curve can only be advanced to a certain amount - (I should have asked what the actual range was, on the bikes I work on, full advance can be anywhere between 30deg and 45deg.). Using 98 octane - the ECU can continue to advance the ignition timing well past the point at which the knock sensors kick in when 91 octane is used. I would guess that the extra ignition advance would be in the region of 10-15 degrees but will confirm that with the mechanic next week.

So - the knock sensors effectively operate as octane identifiers - which is exactly what they are designed to do. The ECU simply keeps advancing the ignition curve until knock occurs - using 98 octane this is later - therefore the ignition timing is further advanced than it would be on 91 octane. All other things being equal (compression ratio, capacity, cam timing and lift etc etc ) - advancing ignition timing results in more power and better economy. This was straight from the horses mouth. RPM has some effect but it is not the only contributor, pre-ignition (knocking) can occur at any RPM under certain conditions. Ignition timing does rely on other sensors than just RPM.

* Final advice was this - 1 tank of 98 is unlikely to show any great improvements for the average punter - he said this was due to dirty injectors and other dirty fuel system components etc which are cleaned over time by the better (or more effective) detergents and additives in 98 octane compared to 91. His advice was that most improvement in fuel economy would occur after the 2nd tank of 98. But he did confirm that the ECU can advance the timing - and will do so based on the signals it gets from the knock sensors - to achieve better fuel economy when using 98 octane.

I will be putting this to the test shortly myself - after the current city-cycle is finished - by using 98 octane in the sub-tank and doing mileage figures from that. Old mate mechanic reckoned that because of the work just done to my rig - I should see immediate benefits because all the fuel-related components are now really clean. . It may well be that the extra cost of 98 is not justified - but I know from experience how much better the Prado responds when using 98 octane and it is nothing to do with fresh fuel vs stale fuel. The engine starts easier, it responds better under aceleration and just *feels* more responsive overall. Now the acid test will be actually doing proper mileage tests to see what benefits there are in terms of fuel economy.

[ratsack Member Find all posts View Profile Close ratsack]

Yeah, I agree with Gosling.
Using 91 octane when 4WD'ng makes 4L feel like 4H. 98 is worlds apart for power, I don't care about if there's a difference with economy. I'll happily pay the 10c more per liter to have more power.

[Torrie 72 Senior Member Find all posts View Profile Close Torrie 72]

So - the knock sensors effectively operate as octane identifiers - which is exactly what they are designed to do. The ECU simply keeps advancing the ignition curve until knock occurs - using 98 octane this is later - therefore the ignition timing is further advanced than it would be on 91 octane. All other things being equal (compression ratio, capacity, cam timing and lift etc etc ) - advancing ignition timing results in more power and better economy. This was straight from the horses mouth. RPM has some effect but it is not the only contributor, pre-ignition (knocking) can occur at any RPM under certain conditions. Ignition timing does rely on other sensors than just RPM.

Eggsaccery. Good work Gosling.

Cheers, Ben.

[Gosling1 Junior Member Find all posts View Profile Close Gosling1]

Got an update on the city cycle today.....

178.8km travelled, all short runs of <10km each over the same roads and same traffic conditions each day. Prior to the work done, the city cycle mileage was around 17l / 100km.

Today - 26.2 litres to fill the tank. That is 14.65 l / 100km. A good improvement and I am pretty happy with that.

Filled the sub-tank with 98 tonight and have started the mileage figures on 98 octane - for city cycle only at this point. I have to go back up to Sydney on the weekend of the 9th August for another round of bike racing at Eastern Creek - so for this trip, I will run on 98 as well so I can get the figures for a highway cycle . The load and trip specifications will be identical to the one I from a couple of weeks ago - 2 x race bikes, tools and gear - so the conditions for measuring the economy will be 100% identical.

If there is any benefit to be gained from using 98 octane - either city or highway, it should become apparent soon enough.

[Gosling1 Junior Member Find all posts View Profile Close Gosling1]

update on the fuel consumption testing......

The last city cycle using 98 octane was canned, as the cook used the Prado a few times over last week and she is a shocking leadfoot - so I have kicked off another city-cycle test today....no point in comparisons if the parameters have changed .....

But last weekend - I had to travel up to Sydney for another round of m/c racing - same load, same bikes, same route - same everything. The total distance travelled using a sub-tank full of 98 octane - was 270km from the fill point in Canberra, to the motel in Sydney.

Filled the sub-tank today - it took 30.79 litres. So that works out to be 11.4l / 100km. This is an improvement of just over 1 litre per 100k in fuel economy compared to using 91 octane ( on the same trip back in July with same load etc - the mileage was 12.5l / 100km).

Everything about these trips was identical - even down to the time of day (late arvo/early evening) that the trip took place. The improvement in fuel economy can only be as a result of using 98 octane. There is also no doubt that the response of the Prado when using 98 is better in every way - acceleration up some of the hills around Goulburn and Mittagong just felt crisper......its hard to describe accurately but the response is just not as 'doughy' as it is on 91, when towing a trailer with a couple of bikes on it....

I will keep using 98 octane for long trips, no doubt. Whether its economically a better bet, is a tough call.....1 litre per every 100km does not sound like much - but to get better economy as well as a snappier response from the motor when towing a trailer with gear - to me its a no-brainer. I think there is some more to come as well - better plugs, synthetic engine oil, good headers and maybe even water injection - should all add up to better mileage in the long run.

Will get some idea about the around-town mileage in a couple of weeks - this could be a different story altogether. I don't know how much of an improvement (if any) there will be in the city cycle......time will tell.

[Torrie 72 Senior Member Find all posts View Profile Close Torrie 72]

update on the fuel consumption testing......

The last city cycle using 98 octane was canned, as the cook used the Prado a few times over last week and she is a shocking leadfoot - so I have kicked off another city-cycle test today....no point in comparisons if the parameters have changed .....

But last weekend - I had to travel up to Sydney for another round of m/c racing - same load, same bikes, same route - same everything. The total distance travelled using a sub-tank full of 98 octane - was 270km from the fill point in Canberra, to the motel in Sydney.

Filled the sub-tank today - it took 30.79 litres. So that works out to be 11.4l / 100km. This is an improvement of just over 1 litre per 100k in fuel economy compared to using 91 octane ( on the same trip back in July with same load etc - the mileage was 12.5l / 100km).

Everything about these trips was identical - even down to the time of day (late arvo/early evening) that the trip took place. The improvement in fuel economy can only be as a result of using 98 octane. There is also no doubt that the response of the Prado when using 98 is better in every way - acceleration up some of the hills around Goulburn and Mittagong just felt crisper......its hard to describe accurately but the response is just not as 'doughy' as it is on 91, when towing a trailer with a couple of bikes on it....

I will keep using 98 octane for long trips, no doubt. Whether its economically a better bet, is a tough call.....1 litre per every 100km does not sound like much - but to get better economy as well as a snappier response from the motor when towing a trailer with gear - to me its a no-brainer. I think there is some more to come as well - better plugs, synthetic engine oil, good headers and maybe even water injection - should all add up to better mileage in the long run.

Will get some idea about the around-town mileage in a couple of weeks - this could be a different story altogether. I don't know how much of an improvement (if any) there will be in the city cycle......time will tell.

Good work Gosling. 11.4L/100! That's fantastic! Certainly something to aspire to. Definitely thinking about ditching the LPG system and optimising the ULP tune.

Cheers Ben.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

Nice bit of info there Gosling.

I always use much larger fuel samples (100L) for calculating this, because I figure there's a higher chance of inaccuracies with small fuel samples (30L), especially when considering we're relying on the filler's auto cut off to measure the quantity. So I've just done a little calculation to find out how much of an under/overfill we'd need to do in order to affect the final result by an entire 1L/100km. Based on the result 12.5L/100km over 270km (33.75L), we'd need to under fill by a whole 3L to effect the result by 1.1L/100km (11.4L/100km over 270km using 30.78L). That provides some assurance, as it'd be pretty hard to accidentally under/overfill by 3L.

By the way, I've kept most of fuel usage info since the day I bought this Prado. I once lined up that information with all of my upgrades (lift, 32" tyres, 33" tyres, ratios, etc) and looked for any clear and consistent changes to the fuel figures. From a long term perspective the biggest improvement was the diff ratios. I also noticed a seasonal change, that is, worse economy in some winters - which surprised me as it seemed to be attributed to using low viscosity engine oil (5W). Short term economy seemed most affected by a air filter condition and of course driving style.

[MelbournePark Member Find all posts View Profile Close MelbournePark]

I drove to the Bluesfest in Noosa from Melbourne, came back over the mountains, with a Oztent on the roof racks, Prado auto 3.4, with an alloy bull bar and tow bar (I bought all that new in 1997). Coming back I stopped at night and photographed to the odomoter - 200,000km. The suspension is raised too, 45mm I think. did that in about 2004. Using GPS mileage and litres from the pumps, I just got under 13 litres / 100km, and drove with my wife and gear, a fridge (eutectic one) etc atc ... using high octane. Changed all the fluids before I left too, including all the diffs. Drove at the speed limits. Did some 4WD tracks as well, but not many.

This is much better economy than I got when it was new.

Oh the tyres are very new too ... but I forgot to increase their pressure ... maybe would have got better fuel consumption.

[Gosling1 Junior Member Find all posts View Profile Close Gosling1]

......I always use much larger fuel samples (100L) for calculating this, because I figure there's a higher chance of inaccuracies with small fuel samples (30L), especially when considering we're relying on the filler's auto cut off to measure the quantity. So I've just done a little calculation to find out how much of an under/overfill we'd need to do in order to affect the final result by an entire 1L/100km. Based on the result 12.5L/100km over 270km (33.75L), we'd need to under fill by a whole 3L to effect the result by 1.1L/100km (11.4L/100km over 270km using 30.78L). That provides some assurance, as it'd be pretty hard to accidentally under/overfill by 3L.........

thanks Glen - I think you might be onto something with the possible inaccuracies over smaller fuel samples of 30-odd litres. I just filled the sub-tank after using 98 octane for the last week and a bit.....38.1 litres to travel 245km - 15.5 l/100km city cycle - on 98 which should potentially be better than 91 - and yet its a 0.85l/100km worse. The difference between getting the better result I got a few weeks ago (on a smaller fuel sample of only 26-odd litres) - which was a mileage figure of 14.65l/100km - and today's result - is only a tad over 2 litres difference overall......

This could mean a couple of things - the auto cut-off on the pump at one station might be calibrated slightly differently to others, or the fuel sample useage for a good comparison is too low, or the 98 octane does not really make much of a difference in the city cycle ?

Anyway the whole exercise has given me some better ideas about how to get better mileage and hopefully some other members can use this. One thing is for sure - I will always do longer trips using 98 octane, especially when towing.

I still intend to do some more mods to get better mileage and will update the thread when these mods have been done and tested...............at the end of the day the Prado is still a big rig and you just have to accept that it won't get the same mileage around town as other vehicles.

[kiwiinmelbourne Lurker Find all posts View Profile Close kiwiinmelbourne]

So if we had to put it in a nutshell, what things will give better economy, what would you list.
In point form?
eg
1.
2.
3.....

[BlakMoth Avid PP Poster! Find all posts View Profile Close BlakMoth]

one with no mods will give you the best fuel economy, but who wants that?


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