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Modifying A Power Fc To Map, Without D-jetro

GTRNUR

By GTRNUR,
in Engines & Forced Induction

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GTRNUR Grand Master

GTRNUR

Posted
Posted (edited)

Hi All,

I was thinking about MAF vs Map. You see all my tuning knowledge is with MAP based ECU's. I want to re-tune my GTR which has a power fc with MAF sensors so i need to re-learn how to tune the car based on MAF.

One of the the firsts thing that everyone usually does is turf the standard MAF sensors and upgrade to nismo or Z32 sensors. They then go about cutting and re-soldering the Z32 plugs on their GTR loom. Its simple and involves connecting the +12V, 0-5v signal and signal ground correctly.

The reason we all know is to maintain a tunable resolution when airflow is substantially increased when boost is turned up. Im told you can tune beyond the max limits of the sensors when the sensors are no longer able to provide tunable sensor information, but your limit is that your stuck with one boost level to maintain the correct AFR's. Thats all provided you have a fuel system to support what your doing. No boost cut/MAF sensor limit cut applies with the FC tune. Downside is that if you change that boost level your tune goes out the window.

Now it occurred to me that it would be possible to very easily connect an after market external MAP sensor to the ECU and achieve a tunable result. The ECU doesnt need to know that its dealing with manifold pressure. All it needs to do is provide fuel and spark, and sense varying loads.

So, here's my idea.

Purchase a Haltech 3 bar map sensor. Then get a 7805 voltage regulator, and a couple of small capacitors to make a small 5V regulated power supply. Connect the output of the supply to the map sensor, and have the sensor output go to the signal input for what was the MAF sensor inputs.

This basic design wouldnt have a full vacuum or max pressure calibration, but if it works it would be easily possible to modify the power supply circuit to make that adjustable. If it works I could fine tune the design later.

Also, the FC Datalogit software allows the ECU to make fuel corrections based on intake air temps with the GTR, so it really has potential to become a decent upgrade.

Why would you do this? Im thinking because its cheap for starters, allows tunability to any boost level so long as you have the sensor for the job. Allows you to ditch the MAF sensors, or keep the stock ones in place to retain that stock appearance.

This modification is so simple to implement that you could literally have a bypass switch to switch between MAF or MAP load sensing, and then just change the ecu maps and your off and running.

Anyone have any thoughts?

Cheers,

Ian

Edited by Vspec R33
Adriano Grand Master

Adriano

Posted
Posted

I believe that the standard computer can be reprogrammed to run maps also. A few things that i can see being a drama are:

(1) The amount of fuel trim that the air temp sensor has in its range, this is essential in getting right, as the change in air density with temp has a monumental effect on AFR's,

(2) although not an outright problem on its own, the ecu has inbuilt scaling which compliments the non linear voltage curve of the AFM, ie:going from 4.0v to 4.4v almos doubles the amount of airflow, and hence fuel im not sure if this can be eliminated totally. I dont know if you would need to make a voltage regulator, as there is already a 5v power supply to the AFM.

T04GTR Grand Master

T04GTR

Posted
Posted

rb26 is tuned with throttle for fuel. map for ignition.

there is not enough manifold to get the resoultion for a map only tune. eg. load rising can tune to a good 14:1 at a point but when lifting of or crusing at the same load point it could be 10:1 or 18:1.

i tried to change my tune to map only but just was not as good a a throttle/map configuration.

so to answer your question no you cant. and this is why the d-jetro is so hard to get correct. it may drive well and make good power. but put a wideband afr meter on it and it tells a differant story

GTRNUR Grand Master

GTRNUR

Posted
  • Author
Posted

Yeah good points... The autronic, wolf and haltech ecu's all use a TPS to map change over point that allows TPS + RPM for lower load tuning and then it switches to map after. I'd have to develop a circuit that could do the same thing i guess. Its possible, but it would be a little clunky as you'd have to adjust a variable resistor to set the change-over point...

All of the sudden its gotten too complicated. ah well..

GTRNUR Grand Master

GTRNUR

Posted
  • Author
Posted

Im still going to re-search how some people have replaced the MAF sensor with a MAP on their standard ECU's. There has got to be a way to make it work with a reasonable result.

Also, the load band calibrations for the FC Datalogit on page 3 of the configuration allows you to define the load points for each voltage reference. I dont see why you cant use 5 or 6 of these load bands for light load tuning, and then use the remaining two points for high load. The ecu aproximates the values inbetween based on averages of the values set in the map. I recall seeing one version of Autronic ecu that had only two load bands for on boost tuning, yet you could calibrate it for any map sensor.

I suspect i'll probably end up selling my FC and getting an autronic or wolf 5 plugin tho... we'll see...

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