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Solenoid injector validation on aftermarket ECU

Diesel Tuning Fundamentals

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13 years back we were looking into running all kind of modern diesel on an aftermarket ECU so logical thing to do is investigate what is needed to run these engines.

In this topic I will concentrate on aftermarket ECU for motorsport use and this is what we came up with. Almost all aftermarket ECU use this BOSCH injector control outline as a benchmarks some even fake it until you maybe make it looking @ the documentation unable to get to the 25A boost current and others we tested over time and may fail take eider off the marked or never enter the marked so do not under estimate the boost peak and hold and coil recharge control needed to run these solenoid injector in a control short circuit as most coil including wiring going to them are under 0,5 Ohm so a short calculation on 14V power supply makes way over 28A coil current without current control.


Boost peak and hold and coil recharge control explained. Please have a look @ the picture.


Red circle in the picture. Boost period 50 microseconds @ 60Vdc start voltage makes 30A coil current and a power surge of 30A x 50V = 1500Watt so thing to look for is dos the ECU have a big capacitor to back this up? Well some don’t but also unable to run these injectors but 25A @ 40V still makes 1000Watt so even for a small injector it will pull some load for a very short time but result on unable to get this boost current later on.

Dark Bleu circle. Peak time. 22,5A for 400 microseconds. In this picture we used the boost voltage for 220 microseconds in current limit mode to reduce the power surge to almost zero on the battery supply as we consume power from the boost voltage capacitors and the remaining peak time will be taken from the 14V capacitors & battery supply.

Boost and peak are critical on precise start of injection. Failing to get to boost/peak current in a given time makes the injector valve operation low resulting in inaccurate fuel injection or even failing to open the control valve in the injector.

Light bleu circle. Hold current. Well this is only there to limit the power consumption to hold the injector valve open. Dropping the hold current by 0,5A on this injector and it will close the injector valve so accurate current control is needed. Still RMS 10A @ 14V makes 140 Watt power consumption per injector.

As last the green critical. Coil power recovery. Takes the energy out of the injector coils so the injector valve is able to close fast. Also part of this back charge in this example is used to charge the capacitors in the system so in all the power surge is minimal on this type of injector diver so wire diameter and length come become less critical. Take in mind some type of ECU even extending the wire loom to the injector by 1 meter will get you into problems.

Inconsistent injector control. In the link below you will find an example on a pilot injection that’s OK but the main injection has a short on boost voltage duration by about 15 microseconds and the result is we now need 220 microseconds to get to peak target current and you can place a question mark if this injector will still function in a hot condition getting a small bit more resistance in the injector wire loom/coil. On this ECU we were getting occasional dropout on main injection.


Other problematic things on injector control. Pilot to all main injection chance over point.

@ some manifold/boost pressure the need for a pilot injection is no longer there and yes on max engine power it will reduce engine power simply as there will be more injector return fuel with multiple injection per cycle that needs to be pumped by the hi pressure fuelpump eating a way some of your engine power. @ the same time your missing out in total injection duration as coil off time on most ECU must be around 100 microsecond and injector response time is about 300 microseconds so in total 400 microseconds can be lost using only one pilot injection so @ 3000Rpm that’s bit over 7 crank degrees your missing out able to injector that diesel fuel.

Pilot injections produce engine power. Post injection should not produce engine power so turning post injections on and off is easy not hitting the smoke limit that is.

Turning a pilot injection on and off maintaining same engine power not jumping up or down on engine power is not easy as you have to estimate injector response time during chance over and @ the same time chance start of main injection timing as well. As you can understand getting this done with big injector and some fuel pressure it can be a challenge to handle this so just looking @ some pilot injection settings not turning them off in the fuel mapping will give some impression on how your able to handle this with your ECU system. A setting for minimum injector quantity will not cut it with big injectors as fuel quantity around this injector minimum on time is very progressive.

Your Posts on Diesel Tuning is highly valuable, thank you.

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