Improving fuel consumption - 95 Series V6 petrol 3.4

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

In the workshop manual - it refers to ECU controlling the auto solenoids with input signals from throttle, engine RPM, vehicle speed, trans oil temp, selector position and a/c compressor - but nothing about engine temp ?

This is where the gear change comes in, as the trans fluid pumps through the radiator, the water temp will heat up the fluid, when the sensor in the trans registers a certain temp, it then will allow 4th gear to be engaged. It works the other way too, as the trans fluid pumps through the radiator, it will assist in the cooling of the fluid when at full operating temp.

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

....One thing I have tried to find on the forum but failed - is info about the spark plugs. Specifically - why does Toyota recommend only dual-ground plugs ?? Is this really an issue ? I would like to put some new Iridium plugs at the next plug change (Xmas) - and these just come in the standard single-ground style.

....As for the spark plugs, yes you need to use the twin ground plugs as a minimum, and the iridium ones are normally quad ground, if your looking at single ground, they would be the wrong ones. One thing I have found is that when using iridium plugs, there is no difference in performance or fuel consumption, you just pay more for them and they will only last for around 60000ks. They cost 8 times as much and you change them 4 times less. you do the math!!! they are not worth it.

The double ground was used to extend the life of the spark plugs. Spark plugs have a shorter life in this engine because we have 6 sparks running from 3 coils - meaning each spark is triggered twice as often as normal. Their is no need for double/quad ground sparks other than to increase lifespan. Now consider the metals used in spark plugs have improved since the 1990's, and prices are different, so TODAY, it's perfectly fine to use single ground sparks of better quality material (iridium, etc). It has nothing to do with "wrong ones" - it all comes down to cost vs practicality. Personally, I spend enough time working on my vehicle so use Iridium.

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

Don't buy a new MAF sensor, as you will be looking at around $1000 genuine and $600 aftermarket, just buy some MAF cleaner and give it a good dose of it according to the directions on the can, allow to completely dry before putting it back in. Also clean the TPS, it is a bigger job to do as you need to take off the induction system, but it will make things run much better too. forget about using 98 octane as that is just pouring money down the drain as the motor was designed to run on 91 and 91 only, there is no benefit using the higher octane fuel. If you can find E10 95 octane cheaper than reg 91 then use it. Injector cleaners are very caustic and can damage the injector nozzles, so only use with a full tank and then only on a long journey to use all the fuel up.

Did you ever replace your MAF? I always thought that may be the reason your economy is so good... but like you point out the cost is huge. Hard to justify spending $1000 to save on fuel.

I'm still on the fence about 98 octane. It obviously has advantages in a tuned vehicle like mine, but we're speaking of standard ones... this engine has knock sensors which detect pinging. The computer does automatically increase the timing of the engine until it senses pinging. This occurs all the time. Logic dictates that high octane fuel should provide some benefit.

Practically speaking - I didn't notice a difference between the fuels with the standard engine, so I just ran E10 and saved money. However, I've read of many people who have noticed more power with 98 octane. Hard to argue with them, considering many people have noticed it, and by design, it's possible.

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

Did you ever replace your MAF? I always thought that may be the reason your economy is so good... but like you point out the cost is huge. Hard to justify spending $1000 to save on fuel.

I'm still on the fence about 98 octane. It obviously has advantages in a tuned vehicle like mine, but we're speaking of standard ones... this engine has knock sensors which detect pinging. The computer does automatically increase the timing of the engine until it senses pinging. This occurs all the time. Logic dictates that high octane fuel should provide some benefit.

Practically speaking - I didn't notice a difference between the fuels with the standard engine, so I just ran E10 and saved money. However, I've read of many people who have noticed more power with 98 octane. Hard to argue with them, considering many people have noticed it, and by design, it's possible.

Yes I have replaced the MAF, but that was only due to chasing a problem with idle and gear change patterns. Something also worth noting is that if you do replace the MAF there are two types for the 5VZFE, so you need to match up the Denso numbers with the replacement ones.
With the fuel octane rating, I have been told by a Toyota Tech that the ECU only recognises 91 octane, if you use anything higher your just wasting money.

[kiwiinmelbourne Lurker Find all posts View Profile Close kiwiinmelbourne]

Yes I have replaced the MAF, but that was only due to chasing a problem with idle and gear change patterns. Something also worth noting is that if you do replace the MAF there are two types for the 5VZFE, so you need to match up the Denso numbers with the replacement ones.
With the fuel octane rating, I have been told by a Toyota Tech that the ECU only recognises 91 octane, if you use anything higher your just wasting money.

I read this the other day. Dont know if its right or not.

Prado petrol engines are equipped with adaptive ignition timing however the rate at which the timing advances is very slow indeed. In addition, if even minor detonation is registered at one part of the RPM range, the entire ignition map is retarded across the entire RPM range.

When high octane fuel is used, the likelihood of detonation is diminished and the engine management system can advance the ignition timing further than that with standard fuel. Resulting in higher efficiency, greater power and torque as well as reduced fuel consumption.

However, in the range of Prado petrol engines, the rate of ignition advance is very slow indeed. This means that one needs to run high octane fuel for many km before any change in performance or economy is fully realised. In the case of the 3.4L V6 in the 90 Series, 5,000 – 7,000 km and for the 4.0L V6 in the 120 Series, 3,000 km – 5,000 km.

Generally after one or two tanks full, the owner will give up and return back to standard fuel because he notices no difference – and does not realise that it takes so long. However if you persist, the benefits are real and quantifiable – more so in terms of fuel economy.

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

I don't believe the ECU can detect octane directly. A dyno tuner once explained something along the lines of what was explained in the last post - the computer automatically increases the timing, but if a knock is detected, the timing is dropped back. I don't recall it being a such a slow process though!

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

I read this the other day. Dont know if its right or not.

Prado petrol engines are equipped with adaptive ignition timing however the rate at which the timing advances is very slow indeed. In addition, if even minor detonation is registered at one part of the RPM range, the entire ignition map is retarded across the entire RPM range.

When high octane fuel is used, the likelihood of detonation is diminished and the engine management system can advance the ignition timing further than that with standard fuel. Resulting in higher efficiency, greater power and torque as well as reduced fuel consumption.

However, in the range of Prado petrol engines, the rate of ignition advance is very slow indeed. This means that one needs to run high octane fuel for many km before any change in performance or economy is fully realised. In the case of the 3.4L V6 in the 90 Series, 5,000 – 7,000 km and for the 4.0L V6 in the 120 Series, 3,000 km – 5,000 km.

Generally after one or two tanks full, the owner will give up and return back to standard fuel because he notices no difference – and does not realise that it takes so long. However if you persist, the benefits are real and quantifiable – more so in terms of fuel economy.

My information has come directly from Toyota themselves, so it would be right, if anyone knows about the ECU it would be them.
There has been many wives tails about using high octane fuel. No one has ever proven their theory about using high octane fuel. there has never been any dyno tests shown, maybe because what I have been told is right.

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

My information has come directly from Toyota themselves, so it would be right, if anyone knows about the ECU it would be them.
There has been many wives tails about using high octane fuel. No one has ever proven their theory about using high octane fuel. there has never been any dyno tests shown, maybe because what I have been told is right.

There is nothing which detects octane mate. Please prove me wrong and find the fuel octane sensors!

I have dyno charts which show it's possible to attain higher kw/nm with 98 then it is with 91 - but of course they're with the supercharger and timing is adjusted.

[scottkz Senior Member Find all posts View Profile Close scottkz]

I don't believe the ECU can detect octane directly. A dyno tuner once explained something along the lines of what was explained in the last post - the computer automatically increases the timing, but if a knock is detected, the timing is dropped back. I don't recall it being a such a slow process though!

Yep quite right, the ECU advances the timing as much as it can until it detects the beginning of detonation then retards it
Higher the octane the longer the timing is advanced so better economy
Lower the octane the knock sensors retard earlier

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

BTW whilst the ECU should be able to adjust for higher octane, I do agree with croozza/Toyota that premium fuels are a waste of money on a standard 5VZ engine (naturally aspirated). Before the charger I used Unleaded (91) or E10 (95) and never had any issues. Some people report better efficiency and power with premium fuels - but is it substantial enough to recover the added cost? I doubt it - saving ~0.5L/100km does not justify the ~20c/L price difference.

Another point to consider is the lack of O2 sensors in the exhaust. The computer has no idea whether the engine is in a LEAN or RICH condition, so fuel injection is estimated. Therefore, it will always be mixed a little rich, and that's quite a waste of 98 going out the pipe!

Most important factor with octane is in regards to pinging. When supercharging, premium becomes near essential to prevent pinging/detonation. On a standard engine it should not be an issue. A few people have experienced pinging with a standard engine, so they run higher octane fuel to solve this - perhaps their knock sensors are malfunctioning...

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

There is nothing which detects octane mate. Please prove me wrong and find the fuel octane sensors!

I have dyno charts which show it's possible to attain higher kw/nm with 98 then it is with 91 - but of course they're with the supercharger and timing is adjusted.

That's right, there is nothing that detects octane rating of the fuel your using in the ECU, so that would mean using higher octane fuels is not only a waste of money, but a waste of time trying to lower fuel consumption. You will not gain any power or torque in a std motor using high octane fuels, unless your state of tune in the motor is poor.
The only way to lower fuel consumption is to have the motor in a good state of tune, correct tyre pressures, having all of that in good condition may seem like you have gained power, but you would have reinstated the correct power of the motor by having the correct tune. Also having both fuel tanks full will add a lot of weight and may seem like you have less power than normal. You only need to have one tank filled each time unless to are going on a long trip.

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

some interesting discussion about 98 v 91 - it happens on every motorcycle forum as well

I had a big improvement in fuel economy on a trip to Sydney last week. Had to drive up for a round of racing at Eastern Creek - so the Prado was loaded up with a 7 x 4 box trailer, 2 racing motorbikes, and all the other gear in the rig - tools, gear etc. Not a full load as it was a solo trip - but dragging the trailer with the 2 bikes adds at least 1/2 a ton.....

33.5 litres to travel 268km. Exactly 12.5l / 100km. This is a great improvement on the recent trip back from Victoria with the same trailer and only 1 250 dirtbike being carried.....

The work done by the dealership before the trip was :

High-pressure injector clean
new fuel filter fitted
Throttle body cleaned (first time in 14 years)
MAF sensor cleaned.

The workshop advised that they needed more time to check the coolant-temp sensor, as it is buried deep in the intake plenum. Almost $300 to check and replace......so we left that job alone as there have been no fault signals to the ECU from the sensor, I was hoping it could be checked without digging too far into the motor.

The result of the tune - apart from the much better economy on the highway - is a better response from the motor. Starting is much the same as it was.

I am now doing the city cycle check and will be back at the end of next week with an update. Hoping that it should be around 15l / 100km around town or possibly even less.

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 ??

...I have been told by a Toyota Tech that the ECU only recognises 91 octane, if you use anything higher your just wasting money.........My information has come directly from Toyota themselves, so it would be right, if anyone knows about the ECU it would be them.....

but then ...

.....That's right, there is nothing that detects octane rating of the fuel your using in the ECU....

So who is right ? The Toyota mechanics ? or not ?

I will do my own check on how much better/worse/no difference, that using 98 octane fuel results in. I know on bikes, that the difference is immediate, no requirement to do thousands of km of travel before any difference is noted.......glad these rigs have got 2 tanks one for Super and one for Standard.....

I just wish they would bring back BP100 in that bowser near the garage shop entrance anybody else remember them ?

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

I couldn't find any exact/specific information on how long it takes to cycle through the advance/retard/advance process, but from what I've read it seems to be constantly occurring, so changes should be noticeable quickly.

From URD's "Additional Injector Calibrators" document:

"The stock system is dynamic and it is constantly adjusting the ignition timing to keep it as far advanced as possible and keep it right at the knock threshold. This gives you the best performance and the best fuel economy."

"The normal things that affect the knock threshold are the octane level of the fuel, the fuel mixture, induction air temperatures, engine temperatures, compression ratio and so on."

http://www.gadgetonline.com/u-tune-aic.pdf


From Toyota's "Electronic Spark Advance" document:

"When engine knocking occurs, the knock sensor converts the vibration from the knocking into a voltage signal that is detected by the ECM. According to its programming, the ECM retards the timing in fixed steps until the knock disappears. When the knocking stops, the ECM stops retarding the ignition timing and begins to advance the timing in fixed steps. If the ignition timing continues to advance and knocking occurs, ignition timing is again retarded."

http://www.autoshop101.com/forms/h40.pdf

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

From memory, the knock sensors only become "active" (for want of a better term) above 3000 rpm.
So the cycle of increasing timing till knock occurs then retarding is not occuring below 3000 rpm where most of our driving in done so there will be little if any benefit from a higher octane fuel when operating in that rev range.
I believe the benefits of the higher octane fuels are partially in cleaning/maintaining injectors and in some instances where you are working the engine hard above 3000 rpm, for example running in soft sand for long periods, think Fraser Island etc.

[juc33_prado Advanced Member Find all posts View Profile Close juc33_prado]

I have a 1999 2.7L RV, only 1 main tank.

Driving around town with a few small highway stints I get 12.5L/100km.

I haven't done any large highway runs without then ending up in the bush or beach so I don't have a 'just highway' figure for it.