Maximum Fuel Delivery - SR5 D4D - or is it??

[Batman]

Guys,

I have just noticed something the other day that I thought was quite interesting?!?

I was towing a 14' tandem lightly loaded, but with a fair bit of wind resistance. I was heading up the Western highway and at the Pykes creek hill climb (pretty steep long climb) noticed that whilst in 4th gear with the pedal flat and holding about 115km/h on the speedo (actual about 105km/h) the instantaneous fuel consumption was about 23lt/100km and wouldn't go higher. I thought to myself at the time that it wasn't very high.

Then on Saturday I was coming home from Bendigo and when climbing Sulky (smaller but long hill coming out of Creswick) whilst accelerating up the hill in 5th gear and increasing speed up to 120km/h (speedo) the instantaneous fuel consumption was again capped at 23lt/100k with the pedal on the boards.

So does this mean that this is maximum fuel flow through the injectors or is fuel delivery being limited by EGT or boost pressure?

Have you guys with SR5's with chips and bigger exhausts noticed higher numbers at highway speeds under full accelleration or big loads?

Steve.

[Quinny34]

I could see higher numbers than that Im sure of it... sounds wierd though... Go back to the dealer and ask to test drive another SR5 and compare if this thread doesnt assist. Just mention your looking to upgrade...

[olcoolone]

A D4D will use as much fuel as required and there is no set max amount.

To give you an Idea on our last trip we were using 35Lts per 100 Kilometers, this was calculated over 500 kilometers.

[djs0276]

I regularly have my instantaneous figures in the mid to high 30's when accelerating away from traffic lights etc. (I don't like to leave it on the instantaneous setting, as it scares me!
What does your show when you're idling? Mine goes up to 99.9L/100
Dirk

[Quinny34]

On a side note, our clubsport changes from L/100 to L per hour when idling.... kinda cool I reckon...

5-6 litres whe idling cold, 2.5 when idling hot per hour....

Completly of topic but thought I'd share... would like to see some of these types of gadgets available in the Lux...

[Batman]

Guys,

I agree with all stated so far. Maybe I didn't explain my question clearly enough.

I have seen numbers as high as 60 - 70 l/100 when taking off from lights etc.

Calculated from the numbers I have seen, and I know it is only a rough indicator, I have seen the following example...

A readout of 23l/100km travelling at 100km/hr equals a burn rate of 23l/hour and a readout of 60l/100km travelling at 20km/hr equals a burn rate of 12l/hour, and both equate to very different fuel consumption figures over a tank of fuel.

However that stated, there must be a maximum fuel rate delivery based on injector size and injector pump flow rates. The first observation I made travelling at 100km/h in fourth gear with a readout of 23l/100km indicates a maximum fuel delivery of roughly 6ml of fuel per second. This means that in one second under the conditions I saw, only 1.5ml of fuel per second per injector is used, which I reckon under full load conditions isn't much.

So is there something else under those conditions limiting fuel delivery or is it at max?

I guess a trip to the Toyota Dealer is in order, I just hope they have a mechanic who can answer me!!

Steve.

[olcoolone]

The engine ECU calculates to amount of fuel needed for a given value.

The given value in this case is engine load.

The ECU will determine 23 Lts is the right amount of fuel needed to maintain forward motion at this given load, any less fuel and you would start losing power and anymore will become a waste product (black smoke and loose of power).

If the ECU gave more fuel it would not develop anymore power and produce higher emissions.

It’s like filling a pool, once the water level has reached the top there is no point in filling it more….the water going over the sides will be wasted.

If you changed down a gear the engine RPM would increase, more air would be sucked in and the engine would develop more power and as a flow on effect more fuel would be needed.

In the olden day (about 10 years ago) you could increase fuel delivery by turning the pump up and this was useful when people fitted aftermarket turbos or exhaust mods where they could get more air in or out of an engine…. But to increase the power once they got more air in and out was to increase the amount of fuel being delivered.

The air fuel ratio (Stoichiometry or AFR) has to be spot on or the vehicle runs lean or rich and the energy in the fuel will not reach its maximum potential.

If a diesel runs lean it will not do the same damage to an engine as petrol will and the same goes to over fueling, you will just loose power.

Getting back to the olden day diesels, once you carried out the mods to allow more air in or out you had to increase the amount of fuel entering the combustion chambers and the only way of doing this was to increase the amount of fuel being delivered by the pump, the down side was you might of only needed more fuel at 2600 to 4000 Rpm but you had to increase the fuel delivery by X% across the board….so you got less power down low due to over fueling and more up top once the air fuel ratio became correct.

This is why older diesel produced black smoke by the bucket load.

Some old diesels ran load compensators that overcame some of the over fueling issues by being able to increase fuel delivery when the vehicle came on boost.

Now to modern times….the ECU programming and a combination of inputs from sensors can get very close to maintaining the ideal AFR needed at any given time.

In short they will only deliver what fuel is required to meet a set target…..no more no less.

[Drew]

I too have seen figure like 70l/100km in low range in soft sand dunes with the 33's make you realsise how much fuel you may need on a desert trip

[olcoolone]

We usally take 200 to 260lts when we go remote, the last trip we used just over 30lts per 100 kilometers and that was for 500 kilometers.

We were towing our camper trailer over virgin ground in low range second traveling at about 5 kilometers per hour for upto 8 hours a day.

It was extreme 4x4ing.