Help Making Fuel enrichment device/controller

Hi gurus!, I am trying to find out how to go about making a fuel enrichment device for a current Turbo project. Now I brought an Arduino UNO starter kit and have a very basic idea of how to do things, I’m hoping this will do the job?

so a bit of background on the system it will be going in to…currently all the additional fuel enrichment is controlled by the vehicle ECM sending a Ma signal to what’s called an EHA (electrohydraulic Actuator) the signal can be anywhere from -10 to +120Ma. so the polarity reverses to cut the fuel off and the higher the milliamps the more fuel is injected.

so depending on what Arduino is capable of i need a pressure transducer input and either just send out a variable ma output depending on the transducer signal, down the line to the EHA with a diode to prevent back feed to the ecm?..will also have to have a switch to cut it off before the polarity gets reversed when you let your foot off the throttle.

or duno if this is possible… the arduino reads the signal from the ECM and with its transducer signal adds the required ma to the ECM,s signal and outputs directly to the EHA…this would be a lot cleaner.
so, it will essentially just me mirroring what the ECM says until it came on boost.

also the rate at which the ma increases with boost will need to be adjustable in the field if possible.

is it possible? or am I dreaming!

any wise words and guidance would be much appreciated.


The current used to control the actuator will be generated by a variable voltage into a known resistance. The resistance of the actuator coil is probably about 20 Ohms, but you need to determine this before going further. The variable current is probably created by a variable resistance in the sensor, although the fact that it can go negative indicates it is somewhat more complicated than that.

You can simulate the actuator load with a resistor/inductor or coil and measure the current with a sensor. This measurement can be processed in the Arduino. To do this you need a sensor that will handle +/- current up to at least 120mA. The sensor will communicate with the Arduino using either an analog (voltage) input or digitally (I2C or UART).

If you get this measurement into the Arduino then you can create a voltage output from the Arduino that is in proportion to that current reading, adjusted as you require. The Arduino can simulate an analog voltage output using PWM, but it will not be able to produce a voltage that will create a current of -10mA to 120mA into the actuator.

A better solution would be a digitally-controlled +/- current source device. You could use two of these, one configured for + and one configured for -, and switch between them using a control signal from the Arduino (unless, of course, you can find a bipolar digital programmable current source).

There is a good discussion of the problem here.


Hi Tristan

I am not trying to be funny here
A diode in the line will prevent negative current for a start. That is what diodes do.
Cheers Bob

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Hi Jeff, OK i will check what the resistance is. what do you mean by

“The variable current is probably created by a variable resistance in the sensor”? i thought it came from the ECU?

and when you say “you can simulate the actuator load with a resistor/inductor or coil” is that to make the computer think it is sending the signal to the actuator?

so im assuming your talking about the intercept the ECM signal and send out its own signal method here?
what about wiring in the pressure sensor input?


Hi Robert, yes i mean if the arduino is connected in parallel with the actuator circuit it would need a diode between the positive connection and the ecm to prevent voltage going back to the ecm? but like you say it will stop the voltage going the other way if the polarity is reversed??


The sensor is the pressure transducer that is providing the input to the controller. A transducer cannot control current directly, because current is dependent on voltage and resistance. But it can control voltage if it knows what the resistance is, in order to generate the correct current. So whatever mechanism is generating the control current has to work into a known resistance, and you will need to emulate that, so you can read the current. I took it for granted that you would read the current and then recreate it, adjusted as required, because I cannot see how using a controller of some sort in parallel with the existing system could work. It might be possible to insert a MCU-controlled variable resistance into the circuit (probably a combination of series and parallel) to fool the ECM into thinking it needs to do something other than what it is programmed to do, but you would need to know a lot more about the internals of the control system in order to even consider that approach, and I can’t see that anyone has ever attempted it like that.

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Hi tristan, Jeff
All pretty ambitious. But I can’t help thinking that playing around with an engine management system could be asking for trouble. I think you would have to know in depth exactly how the whole system worked.
But there is probably no perfect way to find out and without reverse engineering I doubt the manufacturer is going to tell you. There are companies by the way who have done this with various systems and offer modified program devices to fit. Don’t know exactly what is involved as I had no need at the time.

I think what Jeff is saying is the normal way to alter current is alter the voltage across a load (resistance or whatever) and you would expect the load to remain constant. A variable constant current supply does just that as can be observed with a current limiting power supply. When in limit mode the voltage will vary as the current limit is adjusted.

I think what Tristan is trying to do is to add a few mA to the control current from the engine management system. Could be easier with a hardware approach maybe. Be careful with the use of diodes as the forward voltage drop may have an impact. If the present system uses a variable constant current source this should take care of that but if it simply varies a voltage it will not. The negative current is the bogey man. How that is arranged is anybody’s guess.
Cheers Bob

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Hi jeff, yes i read the discussion you taged in you first post, thats pretty much exactly what im trying to do…got a bit heated in the end, not sure if old mate end up making a device but either way it was a bit above me the discussion anyway. might have to watch a few more videos to understand whats going on.


hi rob yea there is always risk involved hence why i thought id ask some people that actually know what they are doing haha and i have searched high and low for a commercially available device but no luck
yes might be a bit difficult trying the parallel method with the reverse polarity
thanks for your input

Hi Tristan,

I’m certainly no car guy but was wondering if there was an aftermarket off-the-shelf device available that would do what you wanted. From what I’ve seen a lot of vehicle modification is usually done by swapping the factory engine management controller for a more configurable aftermarket one like the units made by Haltech.

Is there a reason you wanted to try and make your own controller from scratch rather than use an existing device for your upgrade path?