Diesel tuning box - a total waste of time.

[tolsen]

The title says it all but I'll add a few more details. I bought one of these boxes and spent most of a day testing it out. I tried all possible settings but did not notice any difference in neither power nor torque. Engine felt actually more lively and powerful without the box fitted.


My box suitably wrapped up for protection and ready to be fitted.


The box came with original BMW and Mercedes Benz plugs. Regrettably the manufacturer had neglected to fit the terminal seals so water will enter and cause trouble pretty soon after installation. The box itself is not weather proof and has to be located in a dry compartment - not so easy on a Smart 450 and there is no guidance in the generic installation instructions.


Tuning box hooked up temporarily and ready for testing. Did the testing without fitting engine cover. Just dropped carpet and left the box accessible on top of carpet above engine. There is no way of fitting this box in the only available dry area (cavity between RHS tail light and fuel filler neck) without removing the terminals out of both plugs. There is just not enough space for the large plugs to feed though the gap available.

Conclusion:
These diesel tuning boxes are probably a total waste of time. Don't buy one or even think of buying one.

What is it and how does it work:
A tuning box connects between common rail pressure sensor and engine ECU. It fools the ECU by lowering the signal voltage from pressure sensor resulting in a higher pressure in common rail, more fuel injected, more power and perhaps more smoke.

Bosch common rail pressure sensor same type as fitted on the new Smart Cdi. Signal output is analogue.


Tuning boxes read signal output from pressure sensor and lowers signal according to a predetermined (mapped) graph as above before outputing modified "tuned" rail pressure signal to ECU. Adjustment is usually possible by turning a knob or operating dip switches.

ECU compares the "tuned" rail pressure signal with specified pressure stored in its MAP. End result is a higher pressure in common rail.

Older tuning boxes were completely analogue. More recent tuning boxes have the prederemined graphs stored digitally. This means they can be made cheaper as only one piece of hardware is required.

Tuning boxes only modify one parameter which is fuel rail pressure. You will fail MOT with one of these fitted when the new MOT test requirements enter into force.

[2minits]

The problem with the smarts and tuning boxes (some new ones are different and alter more than just fuel pressure) is they only alter the fuel rail pressure, which is fine until the pressure sensor in the rail realises what is happening and drops the pressure the car is supplying to compensate for the increase in pressure the box is causing...so you will see a performance increase for a short time..sometimes it's minutes....sometimes hours but the car does learn it...
The newer boxes alter pressure, injection time and duration, and boost pressure...they are an altogether different animal, but The price shows the work they require to get them to work properly all the time (development costs etc..)

[tolsen]

Tunit boxes cost 490 pounds and connect between fuel rail sensor and engine ECU. They can therefore only manipulate the analogue fuel rail pressure signal and nothing else.

[tolsen]

I have confirmed that the tuning box is doing what it is supposed to, that is to lower signal voltage from rail pressure sensor.

I hooked up a Fluke multimeter and measured difference or drop in signal voltage, before and after the tuning box. Result is shown in table above. 1 is the lowest setting and 8 is a higher setting. Engine was loaded similarly as going up same hill at constant speed at 2000 RPM.

Next step was to confirm whether the engine ECU was smart or whether it was being fooled. An easy check when you have the tools. I used my Winstar Magus diagnostics kit:

Winstar has a facility whereby one can monitor both specified rail pressure and indicated rail pressure at same time, see to the right of above screenshot. Indicated rail pressure in this case is the "fooled" rail pressure since the tuning box has lowered rail pressure signal voltage.
I confirmed that the ECU was constantly adjusting pressure such that indicated or "fooled" rail pressure would be nearly identical to specified rail pressure. There is some transient effect in above screenshot as the two pressures are slightly different but not by very much, only 8 bar.
Confirmed the above for a range of tuning box settings.

My conclusion based on above tests is that the ECU is being fooled and that the tuning box indeed is doing what it should which is to increase common rail pressure. The higher pressure should in theory result in more power. We shall do some further tests tomorrow and perhaps confirm if there is more power and torque.

[tolsen]

The tests have been successfully completed. There is in fact a very modest improvement both in power and torque but too small to be detected by my butt dynomometer. All tests were carried out on a 6% gradient stretch of A957 just south of Durris Bridge.

Test A: Carried out in 6th gear. Testing ability to pull uphill at lower revs.

Test B: Carried out in 5th gear. Testing ability to accelerate uphill at higher revs.


A very modest improvement indeed. Who wants to pay nearly 500 pounds just to go 8 km/h faster up a dull Scottish hill?

[PikesTnt]

Thanks for the report - very interesting, even to those of us with petrol engines

As you say £500 to go a wee bit quicker up a hill doesn't sound worth it. Apparently, in the 60s they used to drill holes all over motorbikes to save weight. A wry comment was that it saved about as much weight as having a p*ss before the race. Likewise with this unit - If you were to empty the boot, the ashtrays and your bowels before driving off, you'd get a comparable performance boost

Sorry if you were having your tea when you read this

[tolsen]

Having proved that tuning boxes are poor value and bad choice it would be interesting to look closer at remaps.
Anybody out there in possession of a remapped 450 Cdi and prepared to share a copy of your remap file for testing purposes please contact me.

[TAIM]

having proved that tuning boxes are poor value and bad choice it would be interesting to look closer at remaps.

You haven't proved anything other than your box is not tuned to your engine.

There are parameters within it that will de-tune the engine as well as up-tune it, some customers will request that the box is de-tuned for economy at the expense of performance increase.

You need to have your box rolling roaded and tuned for your engine and then you can come back and make your statements about the effectiveness of it.

I can categorically state having owned a (tuned) box for the last six months that they definitely provide a more than substantial increase in torque and power output...(44bhp upped to 64!!)

I have a dyno graph that proves it, and a daily performance that also proves it. (it's on here somewhere)

I can also catergorically state that the power increase does NOT go down as the ECU supposedly learns that there is a box present... the performance I've experiencing day to day is just as good as the day I had it tuned up.

They definitely work, they definitely work well, and the performance definitely stays the same day after day.

[tolsen]

You haven't proved anything other than your box is not tuned to your engine.

There are parameters within it that will de-tune the engine as well as up-tune it, some customers will request that the box is de-tuned for economy at the expense of performance increase.

You need to have your box rolling roaded and tuned for your engine and then you can come back and make your statements about the effectiveness of it.

I can categorically state having owned a (tuned) box for the last six months that they definitely provide a more than substantial increase in torque and power output...(44bhp upped to 64!!)

I have a dyno graph that proves it, and a daily performance that also proves it. (it's on here somewhere)

I can also catergorically state that the power increase does NOT go down as the ECU supposedly learns that there is a box present... the performance I've experiencing day to day is just as good as the day I had it tuned up.

Don't do (the brand) any more uneducated disservice until you have had your box tuned for your engine.

They definitely work, they definitely work well, and the performance definitely stays the same day after day.

I agree with the last bit as I had confirmed that during the tests carried out.
I see thowever that TAIM knows as little about tuning boxes as he knows about torque. No rocket science goes into the design and manufacture of these crude devices. In spite of fancy claims made by manufacturers, all that is manipulated is an analogue rail pressure signal, see description on how they work in post 1 and post number 4.

[tolsen]

Above shows the fuel injection tab in WinStar.

Fuel is injected twice: A tiny preinjection followed by the main injection.

On my 2002 Cdi only the following parameters can be modifed in a remap to improve power and torque output:

• Rail pressure.
• Injection angle for start of preinjection.
• Injection time period for preinjection.
• Injection angle for start of main injection.
• Injection time period for main injection.

Preinjection does not add much to power output so there are only 3 parameters that are worth while modifying:

• Rail pressure.
• Injection angle for start of main injection.
• Injection time period for main injection.

Turbo boost pressure is regulated mechanically and not under control by engine ECU.

Tuning boxes can only modify one parameter (rail pressure) which explains why there is only a modest improvement in power and torque.