low impedance injectors, use resistors?
 

i have a 95 with the ms pnp and i was planning on running 440cc injectors from a turbo supra, from what i gather they are low impedance. So would it be better to use the resistors or the pwm feature? i searched but i didn`t really get my question answered, thanks!

I would recommend using resistors.

Hey this is something I may need to do soon as well. I have wondered for some time what sort of resisters will I need? Figuring out the correct resister value to reach an ohm load I can handle, but often I see people selling injectors with resisters and they have four little aluminium finned blocks. I realise those little blocks are the resisters but are they really necessary? Couldn't one just wire in normal resisters as available from radio shack and the like? How hot do they really get? What wattage will we need?

I have been around long enough to know that anything that is anodized blue aluminium Just HAS to make it go faster, and will therefore find its own buyers. But are they just snake oil or is there a real need for that level of cooling?

I use 10 ohm 10 watt resistors from radioshack on my dsm 450s. I've never felt them get hot.

I had a feeling that would be the case, thanks man.

well if thats the case im going to the shack, unless anyone else has anything different to say

Note the top of my intake manifold:
http://lh6.ggpht.com/_tMYIeupe-9Q/St.../Photo0055.jpg

Do the damn thing.

Most injectors flow about 1A of current through them during use. Lets assume 2A to be safe. P=V*I=14*2=24W. Remember, you are not constantly running them at 100% duty cycle, so they will be cool at idle with no load. Not so for 4k rpm boosted. Ever touched an injector that is shorted to ground accidentaly? Its hot like FUCK. You can easily burn yourself. So yes, you do need the resistors with the heatsinks on them.

Jim

I'm at this point too... I've got the 430cc from my 7mgte (2.9ohms?) and am trying to decide on adding resistors or using the PWM feature. Some searching said that if you use the PWM feature, you might also want to add a direct ground line (to the MS ground location) from the grounded side of R37/R38 to prevent noise... is this right? Also, can't defintetly find what our peak hold amps are for our application, so saying 2 amps is a 'safe' figure, we'd need about a 4.1ohm ~25watt resistor per each injector, or 11.1ohm for a 1amp current (according to DIYauto calculator a little more than 1/2way down the page) calculator

So far you guys are saying go the resistor route... so why NOT use the PWM feature on the MSPNP? What is being overlooked/wrong?

If you run the Hi-Res code, the PWM feature is doa. Hi-Res uses the PWM register for the fueling calculations yielding better fueling control at the cost of no Peak and Hold injector control.

-Rouphis

Those ones?

I personally never liked using individual resistors and wanted a cleaner look. I have some friends with lots of Honda parts and I grabbed one of their resistor packs that come on some Hondas. Looks like this:

http://www.mattjohnstonrally.com/cor...8/DSCN0437.jpg

Wiring is simple too. Here

^ thats exactly what I use , running Supra injectors. Works great.

The shack resistors or the resistor box?

Sorry, the Honda resistor box.

http://img383.imageshack.us/img383/7924/diy001a9ne.jpg

or

http://jgsturbo.com/injres.jpg

Needed when using low impedance injectors (such as DSM injectors). Gold anodized finish with solder lugs. 10ohm / 50 watt, no heat sink needed (built-in). Install 1 resistor inline with each injector on the positive side.
TA048 Set of 4 resistors- $19.99

JGS Precision Turbo

10 watt resistors is living kind of dangerously. 20 or 25 watt would be better.

Ive been emailing Matt back and forth about this topic today. If you would like to run just a single resistor per channel you can use a 3 ohm 75+ watt in line

It shouldnt matter if it is on the positive side or the megasquirt side of the circuit right? the current flowing thru the injector will still be limited .

3 ohms is the minimum required to where you shouldn't damage the injector drivers in the MS. It all depends on how much current you feel comfortable running through the injectors, but prudence dictates running a bit more resistance.

It doesn't matter where the resistor falls in circuit.

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.

i have an AEM 10 channel lo-z injector driver box for sale, if that interests you PM me...

Thank you for your words of wisdom ;). I guess I won't worry about installing them then.

that sucks the resistors wont work for you Cspence, the pack came off Rotornuts car, and he was running low imp. RC550's with a Link ECU.

:dunno:

I think they'll work from what Joe Perez was saying. How did he have them wired? Do I just splice a resistor into the 12v source for each injector?

yeah! they were wired in right before the ECU in line with the signal wires....

Hmm. You've got a 1.6, don't you...

Normally, I'd say to splice them into the line between the injector and the ECU. But yours are banked at the INJ harness.

Ideally, you want one resistor per injector. Mostly, this just keeps the heat down. If you run one resistor per two injectors (ie: inline with ECU on a 1.6 harness) you'll have ~ 6.5 ohms series resistance, and be dissipating about 25 watts.

So yeah, it'll be a little messy, but you kinda need to cut apart your INJ harness so you can do this. It doesn't matter whether you put the resistors on the +12 side of the injectors or the ECU side.

will the honda resistor box work using a stock ecu? The car runs and drives with stock ecu and original fuel supply. I want to limp this for now untill i get ms, i have 450 injectors yet to be put in. Also have honda resistor boxes sitting around, so if i can use that as a band aid for now id rather not see the car sitting around.

It depends.

You can easily enough measure the resistance across it with an ohm-meter to see what the resistance is. You're looking for something in the general vicinity of 8-12 ohms.

There are some downsides to this.

First, it's my understanding that the Honda box has five wires, with all of the resistors joined at one end to a single common. Thus, the box must be installed between +12 and the injectors, rather than between the injectors and the ECU. Since the +12 supply to the injectors is commoned to a single wire within the INJ harness, you will need to remove the INJ harness from the car and cut it completely apart, bringing out separate +12 feeds for each of the four injectors in order to connect them individually to the box.

Second, running any kind of resistor in series with a low-z injector defeats the purpose of having a lo-z injector in the first place. It removes the ability of the injector to be "slammed on" with a large amount of current at initial opening. I have never done back-to-back measurements, however I would not be at all surprised if a lo-z injector which was so wired exhibited poorer turn-on performance than a hi-z injector of equivalent flow rating.


But the most important factor here is application-specific. If you want to put this box between your stock ECU and some 450cc injectors, then no, that will not work at all. 450cc injectors are way too big to run on the stock ECU.

That is exactly what i was looking for. thank you.
Another question, i have tried to look for this. why dont people use more parts from a 323. will the injectors from the gtx do me any justice? Or would i throw parts at this fuel system all day but still need an ecu? Ill be running an internal wastegate at 8psi.

as a counterpoint, I should mention that running the JBPerf injector drivers for low impedance injectors works very well except that they take up far too much space in my case and I have a lot of extra wiring and soldering that could fail and cause problems.

https://lh4.googleusercontent.com/-8...0/DSC_3370.JPG

https://lh4.googleusercontent.com/-6...0/DSC_3372.JPG

[QUOTE=DXO;515982]I personally never liked using individual resistors and wanted a cleaner look. I have some friends with lots of Honda parts and I grabbed one of their resistor packs that come on some Hondas. Looks like this:

http://www.mattjohnstonrally.com/cor...8/DSCN0437.jpg

Wiring is simple too. Here[/QUO

I took the factory wire loom off and none of my wires are the colors in this diagram. I have a 97 with emanage ultimate ecu 440cc injectors trying to upgrade to low impedance 1000cc rc injectors. Will this work for me as well?

This is understandable, given that the diagram you linked to is for a Honda Accord rather than a Mazda Miata. Rather interestingly, the color codes for the 1976 VW Beetle and the 2014 Lamborghini Diablo also don't match up.



See post #48.

You could make it work by ripping apart the stock injector harness and completely re-wiring it. But it would be less work to splice individual resistors into the wires between the injectors and ECU, and even less work still to run the correct injectors in the first place. Lo-z injectors used to be new hotness, now they're pretty damn antiquated.