My supra injectors were 2.98 -3.17 ohms..... use resistors. I see why now. :)

Hang on, so you mean I can stick one 3 ohm 75w resister on each of the injector outputs at the MS. So inside the car, 2 total resisters and be fine? I would MUCH rather do that and not have to find a home for 4 little (brittle) ceramic bricks under the hood.....

You could always use a peak&hold driver board...

Jean

Well two little discoveries that end the debate for me. I had another look thru the megamanual and it clearly states NOT to use one resister for two injectors. So that is out. The other thing is I have found the little aluminium 25watt 10 ohm resisters on ebay for £2 each ($3). They are gold not blue so wont go as fast of course, but at that price I will eat my words and get a set of them as it is just the easy route. And frankly if old Ben from Diyautotune says that is the best way to go I am inclined to believe him.

So case closed for me, I will just follow the herd on this one.

FWIW, I will be going this route very shortly. I don't mind running resistors ( and I have no problem suggesting them on a budget), but I'm going to focus on cleaning up my install as much as possible over the next few months, and part of that is tidying up my engine bay wiring so it doesn't look like crap.

Meh. Even at steady-state they're only going to see 14w, and in reality they're hardly ever running at anything remotely approaching 100% duty cycle. Your turbo will melt before the resistors do.


This is definitely the best option. By installing resistors inline, you defeat the super-quick response which is the hallmark of P&H injectors. In this mode, chances are excellent that they'll actually run slower than conventional saturated injectors.

Jean's P&H board, by comparison, actually drives the injectors as they were meant to be driven. It gives them full power at initial opening, then throttles them back to holding current by using PWM. You'll get much better response out of them, which directly translates to better idle quality and lower idle emissions. And c'mon, it's only $61 shipped with all components. I've spent more than that on lunch before.

Peak&Hold Injector Driver Board for Megasquirt

Dammit Joe!!! just when I had given in, now you show me the right way and i need to find another $60.

Oh, quit your bellyaching. For you it's only £40, and 40 is less than 60. :D

This is the best way, by far you get to run the High_res code AND low impedance injectors.

So where is the junction box that is the black/yellow wire? I know the 4 black ones go to your injectors. I also saw where someone spliced all 4 wires from the injectors that weren't hooked up and put them to the black. Also what are some good cranking pw's and accel enrichment settings for theses lo-z 440's? Thanks!

The so-called "junction box" is merely the place where +12 is coming from to supply the injectors. On your car, this is a white/red wire which leads to the injector harness. The resistors go between +12 and the injectors.

In the standard Miata INJ harness, the white/red wire is connected to all injectors in common, so you'll need to rip the harness apart and run discrete supply wires from each injector to the resistor box. This is the burden to bear for running the Honda box- all resistors are internally commoned on one side, so you can't place them between the injectors and the ECU, where the wiring is already discrete and thus easier to tap.

Under the intake manifold there is a sub harness that connects to the water temp sensor on the back of the head and to the injectors. I just pulled this out and wired the Honda resistor box into this. It helped that i had the Honda harness to strip apart to make this easier tho. It looks very stock with it like this.

so i am wiring this resistor box in before the injectors. The resistor box has one 12v constant coming in and 4 coming out. So in theory i am just grabbing the 12v injector power before it gets split into 4 and letting the honda box do that, right?

Absolutely correct.

Ok, new question
 

So I have injectors that have 12.6 OHMs, and my 90 miata runs 13.8 OHMs. Should I reduce then down to this amount or will they be fine?

FYI i have successfully used these on a low imp setup on hi res code. . . 1 per injector channel

3 ohm 50 watt resistor

It doesnt get hot at all.

You're fine.

The difference between 2 ohms and 12 ohms is huge. The difference between 12 ohms and 14 ohms is trivial.

So, the resistance in my honda resistor box is only 6.5 ohms, and my injectors are 2.9 ohms, so thats 9.4 ohms, is that cool on the megasquirt?

I just bought some low impedance injectors and they came with the individual resistors like the gold one Brain posted.....I measure 5.5 ohms across them but am second guessing if that's enough resistance (7.5 - 8 ohms with the injector). Should I just buy some 10ohm resistors or should the ones I have be sufficient. Also as far as install goes, these just get wired in-line with the 12v lead going to each injector, correct?

Let's say your injectors are 2 ohm, so the total series resistance is 7.5 ohm. Assume 13.5 volts supply, so you'll get 1.8A per injector, total of 3.6A per driver assume you're running two channels.

The current limit on the MS's driver circuits is set at 14A.

You'll live. In fact, the injector performance won't be quite as bad as what the folks running 10Ω have to live with. It'll still make baby Jesus cry, just not as much.