Improve your Fuel Economy and Performance

(14-10-2012 08:25pm)stodman Wrote:  So here is the question what is the mechanical difference between the td4 and sd4 engines?

They have different injectors and a bigger turbo plus the engine management software is different.

There may be other items as well.

Ceebee, just as a matter of interest, on this particular unit I'm guessing the plug that goes into the common rail only has three wires, yes?

I'm Just looking at that website and its only showing just this one three wire connection. Is this right?

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(14-10-2012 09:21pm)Evo-king Wrote:  They have different injectors and a bigger turbo plus the engine management software is different.

There may be other items as well.

I don't know about this LR motor, but typically other alterations between low tune and higher tune engines can include modifications to crankshafts, additional drillings to facilitate piston cooling jets, etc. it would need someone from LR to confirm or otherwise.

Fujisan, fromwhat I remember it Is just three wires going to a multiplug, which inturn fits into a plug that you disconnect on the left side of the common rail plug ( when standing in front if the car looking into the engine bay).

Thanks, that's what it looks like on the web site and not uncommon.

Many will know what it is connecting to, but some may not, so for those people...
The thing the tuning box is connecting to is the common rail pressure sensor. Basically the tuning box is just connected between the pressure sensor and the ECU. So far, so simple. The pressure sensor is a sender only device, that is to say, it does not receive information from the ECU, it sends information; in this case, the pressure inside the common rail. Once again, so far so simple.

The three wires are a five volt supply from the ECU, a zero volt or earth connection, also from the ECU and finally, most importantly, the pressure sensor output, to the ECU. This will vary between 0v and 5v. Typically around 0.5v at idle, maybe 3.5 at full power and should be pretty linear between the two voltages between idle power and full. A very simple device, performing a very simple function. That is to confirm the injection pressure in the common rail, is the same as the expected pressure on the ECU map, which in turn depends on all of the other factors at the time, I.e. throttle position, air temperature, air density, etc, etc.

The tuning box can only possibly output a voltage within the same range as the sensor normally sends to the ECU, simply because if it does not, then this is when the ECU detects that the signal is implausible taking into consideration all of the other signals it receives. So in essence, all the tuning box can do, is send a slightly different voltage to the ECU than expected in order to affect the power output.

By way of example, if you press your accelerator to give around 1800 rpm and are expecting to have x amount of power, the sensor may typically be trying to send a voltage of 1volt to the ECU, which would hopefully correspond to the ECU map for those conditions. But, the tuning box only sends say 0.9. The ECU notices this disparity and increases the pressure to get to the correct reading of 1volt. Very simplistically, Increasing the pressure in the common rail, will give more fuel injection for the same throttle input, and therefore more power output. This is where the advertised power increase comes from.

But this is where it also starts to fall apart. If you are using more fuel for the same throttle setting, you are actually consuming more fuel than you would have done previously, or have increased smoke, or higher emissions, so you certainly should not fit one of these boxes if you have a care for the environment. So - If you are overtaking, you need and get the extra power, but once you don't need the power, you will naturally ease off the gas. And guess what, you will now actually need less throttle than before to maintain your desired speed, so your engine will be working at proportionately less fuel input, less RPM and this is where any claimed fuel economy will come from.

In summary, when you need more power you will get it, but maybe at the expense of over stressing some components, and certainly at the expense of fuel economy, increased emissions etc, and when you don't need the power, you may gain a few percent on the economy side. Pretty much what the tuning box manufacturers claim, to be fair to them.

But that's all the box can do, it's a simple, or maybe even a slightly complicated circuit that acts as a voltage changer between the rail sensor and the ECU. It can't map anything no matter what anyone says. If you think about it, it really can't. All it can do is take the actual voltage from the sensor and send a different value than expected to the ECU. I'm not even sure it is remotely plausible to do anything clever here. Maybe if the throttle position was connected to the tuning box, then the box would know how to change the voltage for best effect, but it doesn't, so it can't.

The box has a tuning dial on it to adjust or alter the 'map' for power or economy. So what? If you re-read my explanation of what the sensor and box do, you can figure out what this adjustment actually does. It will either decrease the voltage for power, or increase the voltage for economy. Nothing more than a resistance change. Do your instructions say to reduce the power dial if you get excessive smoke, or engine warning lights, or worse, it goes into limp home mode? Well guess what, you probably had the setting too high and the ECU knows from it's map and the inputs from the other sensors, that the rail sensor signal is simply not plausible, and therefore shuts down into a safe mode.

Some of you may now be bored, I apologize. Some of you may have read this far and don't care, that's OK too. Some may not be convinced of what I have said, that's very easy to check. Just ask anyone in the auto industry how the common rail pressure sensor works. A few more of you may well be questioning how these tuning boxes manage to deliver all of the claims made by their manufacturers. Well, in that case ask them. I would be very interested to find out if it is uniquely different from what I have just described. (Although I'm pretty sure I have an idea how they justify the use of the description "map")

And bear in mind, the bottom line is all you are doing is adjusting the common rail pressure to be a little higher than the ECU wants it to be, in any given circumstance. You have not updated any other engine components to deal with the increased power. This may not be a factor if you don't use all the available power a lot of the time. But if you do, like when towing maybe, or if you habitually like driving it like you stole it... Then you may be, just may be getting close to something failing, maybe catastrophically, almost certainly expensively.

You all are perfectly free to make your own choices in life and for some people, these solutions may be just fine. I know that many people use them in older vehicles and they perform pretty much as advertised. But taking everything into consideration and in a modern engine system, it's certainly not for me and I certainly would not recommend it.

The Americans have a great 'rider clause' for these situations. "Your mileage may vary."

Take care out there.


(Minor edits for clarity only.)

Thxs for the lesson Fujisan. What about an ecu remap? Do you know how they work?
Personally, I think I'll leave it all alone and just enjoy the car as is...

Fujisan, full respect where its due for your detailed explanation above.

The instructions do indeed state that you can adjust the tuning box if you get problems with the ecu etc, so you seem to be bang-on!

There are 3 variants of these boxes, I went for the economy box as I was happy with the performance of my SD4, but there are also power and towing boxes available.

In at nutshell, all I want is better MPG, (ideally above 40 on my routine trips to work) but I am now thinking that maybe I settle for a lower figure rather than cause damage to my engine in the long run.

It would be interesting to hear from any forum members who have had these boxes fitted to previous cars over a longer period of time to see if they have experienced any issues?

(15-10-2012 12:19am)Craig_d1 Wrote:  Thxs for the lesson Fujisan. What about an ecu remap? Do you know how they work?
Personally, I think I'll leave it all alone and just enjoy the car as is...

A full ECU re-map is an altogether different animal. A professional re-map will involve getting the car into a controlled environment and on a dyno, so that the differences in tuning are only ever mainly attributable to the new map and not any other variable, and so that the difference in tuning can be accurately measured on the dyno. Because it is done in the ECU, It should also take account of all of the other engine sensor inputs, to ensure that within the parameters of the remap, other results are not unduly compromised (such as soot production, NOx levels etc.)

Of course there are differing qualities of remaps as well and the best will generally be quite expensive and involve either buying a new ECU chip or in some cases a complete new ECU to swap into the car. These would generally be regarded as a better solution as its easier to reverse to tune by putting your original ECU back in.

Please don't take any of this as an endorsement of either ECU remapping or tuning boxes, I'm simply answering the question.

Back to tuning boxes for a minute. Offering various types (i.e. tuned for economy or power, etc.) is a relatively simplistic thing to do as all they need to do is either increase or decrease the voltage that their tuning box sends to the ECU. If you think about it, you can probably achieve most of this yourself, by backing off the so-called 'boost' control/potentiometer. Reduced boost = less pressure = greater economy than higher boost levels.

So let's say that at 2000 rpm the common rail pressure sensor would normally transmit 2 volts to the ECU, then perhaps (in a very simplistic example) you can see how a 'tuning box' tuned for max power would send say 1.5 volts, causing the ECU to boost the pressure a fair bit. When tuned for a more modest power increase would send only perhaps 1.8 volts, causing the ECU to increase the boost pressure, but not as much. And a box tuned for economy might send 1.95 volts resulting in only a minimal boost gain. I suppose it's also possible in for a 'tuning box' to actually be set up to send more than the expected voltage to the ECU, which would fool the ECU into thinking there was too much pressure and actually reducing the boost applied, but unless a permanent reduction in power was desirable, I can't really see the point.

Please don't take these voltage figures as at all representative of an LRE, or of any other vehicle, I only use them to illustrate the principle involved.

Anyway, I had best shut up now as I really do run the risk of boring the heck out of people.

For those with a bit of spare cash and not worried about Fuel economy try http://www.prindiville.co.uk/ I'm not spamming but a good friend of mine recently had his Mercedes SLK AMG done by these guys and he is extremely impressed with what they have done for him.

(15-10-2012 10:48am)FujiSan Wrote:  A full ECU re-map is an altogether different animal. A professional re-map will involve getting the car into a controlled environment and on a dyno, so that the differences in tuning are only ever mainly attributable to the new map and not any other variable, and so that the difference in tuning can be accurately measured on the dyno. Because it is done in the ECU, It should also take account of all of the other engine sensor inputs, to ensure that within the parameters of the remap, other results are not unduly compromised (such as soot production, NOx levels etc.)

Of course there are differing qualities of remaps as well and the best will generally be quite expensive and involve either buying a new ECU chip or in some cases a complete new ECU to swap into the car. These would generally be regarded as a better solution as its easier to reverse to tune by putting your original ECU back in.

Please don't take any of this as an endorsement of either ECU remapping or tuning boxes, I'm simply answering the question.

Back to tuning boxes for a minute. Offering various types (i.e. tuned for economy or power, etc.) is a relatively simplistic thing to do as all they need to do is either increase or decrease the voltage that their tuning box sends to the ECU. If you think about it, you can probably achieve most of this yourself, by backing off the so-called 'boost' control/potentiometer. Reduced boost = less pressure = greater economy than higher boost levels.

So let's say that at 2000 rpm the common rail pressure sensor would normally transmit 2 volts to the ECU, then perhaps (in a very simplistic example) you can see how a 'tuning box' tuned for max power would send say 1.5 volts, causing the ECU to boost the pressure a fair bit. When tuned for a more modest power increase would send only perhaps 1.8 volts, causing the ECU to increase the boost pressure, but not as much. And a box tuned for economy might send 1.95 volts resulting in only a minimal boost gain. I suppose it's also possible in for a 'tuning box' to actually be set up to send more than the expected voltage to the ECU, which would fool the ECU into thinking there was too much pressure and actually reducing the boost applied, but unless a permanent reduction in power was desirable, I can't really see the point.

Please don't take these voltage figures as at all representative of an LRE, or of any other vehicle, I only use them to illustrate the principle involved.

Anyway, I had best shut up now as I really do run the risk of boring the heck out of people.

one of the best explanations i have read - thanks for taking the time to share this.

Well I'm not going to bother with it! To be fair I have had over 40 mpg from mine on a long run! Just by changing manually and when accelerating on the motorway, flicking it into 6th on Commandshift so the system doesn't change down.