Injectors and resistors

[Colin Wiltshire]

Some pics of the injectors and resistors planning to install,

Injectors are unknown size as can't remember.


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[GalantOnly]

Almost off topic... Must the resistors be wired on the ground wire or 12V wire of the injector? Or is it doesn't matter?

[Colin Wiltshire]

Almost off topic... Must the resistors be wired on the ground wire or 12V wire of the injector? Or is it doesn't matter?

I don't know yet, but I'm sure someone will know

[GalantOnly]

I'm asking because in the wiring manual to my cars stand alone ECU says that the resistors must be placed "on the +12V side of the injector". But the car is actually wired another way around with resistors on the ground side...:thinking:
So it may make no difference?... I hope :)

[swinks]

Colin these are US manufactured aftermarket 540cc injectors for Evo 1-3.
Wiring resistor pack will apply like any other low impedance injector injectors. You can't mess with wiring, otherwise you will brick ecu.

[swinks]

Alex, IIRC +12V feed is common in our injectors and ground is like individual signal, hence you wire up resistors in +12v line individually for each injector. Have seen somewhere utilized two stock resistor packs from Evo in Galant v6 engine, each pack for separate bank.

[GalantOnly]

Thanks Tomasz. But do you know if is it a problem to wire 6 resistors onto each ground signal from ECU, instead on the each 12V feed?

[foxdie]

Hmm, I was under the impression the injectors were switched negative (ground) by the ECU, I checked my old EFI ECU Pinout thread (http://www.clubvr4.com/forum/showthread.php?59222-Definitive-EFI-ECU-Pinout-(KS-Mod-friendly)) but it appears its not made clear. Let me see if I can dig up the ol' Galant wiring diagrams...

[wintertidenz]

You could possibly use a resistor pack from an FTO or GTO as well. Not sure how they plug in however.

[foxdie]

Technical time! (wow, not done this in months!)

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Looking at the diagram, the injectors are switched to negative / ground by a transistor / MOSFET in the ECU, so there'll be a (semi-)permanent +12V feed that the injectors connect up to.

Ps. This diagram is for a 6A13 SOHC (engine from a N/A V6 Sport), although it should still apply for VR-4s at least for most of the systems it could possibly be incorrect for VR-4s. You have been warned.

[foxdie]

As for the resistance / impedance, the inspection manual lists the stock injector resistance (again, for a N/A V6) around 13 to 16 Ohms at around 20'C.

And from another (reliable) source (@Gowf); The stock VR-4 injectors are 390CC High Impedance.

[foxdie]

As for wiring in the injector resistor pack, Google seems to favour installing the resistor pack between +12V and the injector, not between the injector and the ECU. That makes sense, as the resistor between the injector and ECU may cause lag.

[swinks]

Yes.
Putting it simpler...
- each bank has separate loom for injectors
- there are 4 wires in loom: +12V feed (common) and 3x individual ground. Can't remember colours.
Common wire splits accordingly to feed each injector. Resistors are needed on each +12V line between injector and loom plug.

You can setup resistor pack like this:
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Obviously you can use dedicated "resistor box" or separate resistors.

[Anderz]

There is no difference if the resistor is on the +12V side or the ground side of the injector
There will be same voltage drop over the resistor in both cases, which means same voltage lower voltage will be supplied to the injector as well in both cases
Just make sure that there is one individual resistor for each injector

[swinks]

There is no difference if the resistor is on the +12V side or the ground side of the injector

I'm afraid there is.
Not being expert but seen somewhere that injectors are solenoids hence it does matter which side of coil you apply resitor.

BTW, and beware, do not to install resistor directly near engine. Heat from heads will change resistance value of mentioned resistors. Best location - firewall.

[Adam.Findlay]

I'm afraid there is.
Not being expert but seen somewhere that injectors are solenoids hence it does matter which side of coil you apply resitor.

BTW, and beware, do not to install resistor directly near engine. Heat from heads will change resistance value of mentioned resistors. Best location - firewall.

they will get hot so make sure they are mounted somewhere where they will not come into contact with other objects (vac lines, IC piping etc etc.)
so firewall would be best.

[BCX]

It's irrelevant which side of the injector the resistor is on, coming from an electronics background. The resistor's purpose here is to limit current to not burn the driver transistor in the ECU. The voltage across the injector will be the same regardless of if you put the resistor before or after.

One *might* argue that it *might* make a difference in an AC circuit as the solenoid is essentially an inductor, but this is a low voltage DC circuit that is PWM (square wave).

It's also worth noting that impedance is not the same as resistance... there is a difference between them. Measuring the DC resistance of the injector doesn't give an indication of it's impedance. Impedance is resistance in an A/C circuit.

The VR4 (infact all Mitsubishi ECUs I've seen) sink injector current. I'd say this is a cost thing as they only need one NPN darlington transistor to do the switching directly from the processor, and I'm assuming there's also a diode to protect the transistor from the spike of the collapsing field created when the injector is 'on'.