Turbo diesel fuel saving idea/question?

[nubbzcummins]

I have the ability to "fool" the map sensor into thinking that it is getting more or less boost than it actually is. Less boost sensed it fuels less and more boost sensed it fuels more. Here is my question/s: Which will actually save me more fuel for higher mpgs...less/more boost sensed? I want to say less boost sensed but will this cause the turbo to build boost slower and put too much load on the motor causing more fuel to be burned? Will making it sense more boost fuel more making the turbo build boost faster/quicker response to grades causing less bog thus less fueling? During my daily commute in o/d at 55mph I am running around 1350rpm and 0-10psi boost depending on the grade. Most grades during my comute I only make a max of 5-7psi.

[SVOboy]

I wouldnt recommend fooling the computer into improperly mixing fool, creating a lean condition while boosting is not good. Rather, I would find a way to make it run less boost.

[tasdrouille]

Do Rams have a MAF? I assume the gurbo is a VGT.

You should do it when cruising at low loads. Tricking the ECU into thinking boost is higher, so it's effectively dialed back. That'll will help with backpressure.

[nubbzcummins]

Originally Posted by SVOboy

I wouldnt recommend fooling the computer into improperly mixing fool, creating a lean condition while boosting is not good. Rather, I would find a way to make it run less boost.

A turbo diesel boosting with lean air/fuel mix is not a bad thing to my knowledge. Being lean helps cool egts in a diesel. Please let me know if this is incorrect.....

[nubbzcummins]

Originally Posted by tasdrouille

Do Rams have a MAF? I assume the gurbo is a VGT.

You should do it when cruising at low loads. Tricking the ECU into thinking boost is higher, so it's effectively dialed back. That'll will help with backpressure.

It has a MAP sensor.....The turbo is stock and pretty sure it is a VGT..... So making it think more boost is there will make it more fuel eff? How does this effect back pressure? I have 5" exhaust BTW.....Please explain your last statements as I'm

[ConnClark]

Boost is not a bad thing. It can and actually does improve efficiency on a diesel in most cases. It is a case of diminishing returns however and you will reach a point where the improvements are off set by the parasitic load it takes to generate additional boost.

Generally a turbo diesel will only make large amounts of boost when it needs it. Off peak load the turbo usually finds a happy equilibrium if its matched to the engine right(Car makers usually do a very good job of this). A properly matched turbo that is tuned for efficiency will actually create more boost than back pressure at cruising speed and load. Unless you know for a fact that its not tampering with your turbo to get it to run at a lower boost level at cruise isn't likely to improve your mileage.

Tampering with other things such as a free flowing exhaust or intake that will increase your boost and will generally help however. Replacing the turbo with a more efficient one will help too. Just keep in mind that all aftermarket turbos are not more efficient. Some are there to just target the performance market.

The only real way to improve mileage by lowering boost is to keep boost low by the way you drive. The turbine of the turbo is driven by energy not recovered by the pistons. Driving in a manner that keeps your boost low is a sign that you are recovering as much energy as possible with the pistons and therefore are recovering as much energy as you can to move you down the road.

[nubbzcummins]

I believe that I need to do some testing on this to find out what works best. Will probly alter boost sensed by map sensor +/- and IAT sensed by map sensor +/- and see what each one shows as far as FE. May do this in severial trials under the same conditions and driving styles to see what proves to be the most FE.

[nubbzcummins]

Altered my boost sensed by the map sensor on the last short tank to make it sense more boost than is there. I used a 33ohm resistor between the 5v supply and the signal. My signal voltage before at idle was in the 1.27-1.3v range and after the resistor was put in it read .3-.5v higher at idle depending on how warm the engine bay got since this was done under the hood and the heat changes the resistance of the resistor some. Cruising it was also sensing more boost but pulling a grade it would not sense more boost than before(2.3v signal). I ran like this for about 1/2 the miles on a very quick refill and got 21.4mpg which tells me this kills my fuel mileage based on driving like the 21.6mpg tank. I then placed the same resistor between the signal and ground wires to make it sense less boost in the area of 1.17-1.2v in the signal wire. The max signal sensed like this is 1.91v vs 2.3v as before and also senses at least .1v less while cruising. So far this tank is along the lines of being a record mpg tank(22.27mpg) and this is driving the same as my 21.6mpg tank. Check out my fuel logs for details. I will see how this tank turns out before I go to other settings.

[nubbzcummins]

Update: Just added a new fuel log with the 33ohm resistor between signal and ground on the map sensor. Idle voltage sensed was 1.18v vs 1.28v normal and max sensed on grades at 55mph cruise is 1.91v vs 2.32v normal. Managed 21.71mpg and 800.3 miles this tank. For my next tank I have it set to where idle voltage sensed from the map sensor signal is 1.1v and max on grades at 55mph cruise is 1.3v. Doing well so far as it seems to be doing slightly better than my last tank. Will have another update in about a week.

[ConnClark]

Originally Posted by nubbzcummins

Update: Just added a new fuel log with the 33ohm resistor between signal and ground on the map sensor. Idle voltage sensed was 1.18v vs 1.28v normal and max sensed on grades at 55mph cruise is 1.91v vs 2.32v normal. Managed 21.71mpg and 800.3 miles this tank. For my next tank I have it set to where idle voltage sensed from the map sensor signal is 1.1v and max on grades at 55mph cruise is 1.3v. Doing well so far as it seems to be doing slightly better than my last tank. Will have another update in about a week.

Doing one tank and changing a variable isn't a valid test due to not filling the tank to the same level each time. You need a minimum of at least three tank fulls on each configuration to draw any remotely valid conclusion.