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Old 03-12-2008, 02:34 AM   #1
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Default Injector resistor pack

So... I spent few days trying to find some info on injector resistor pack... Where the hell can I buy one and does anyone have any wiring info?
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Old 03-12-2008, 02:37 AM   #2
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are you just trying to turn a low impedance injector into high impedance? If so, you can just buy a resistor from radio shack with the correct ohms. Like resistance of a miata injector minus resistance of low impedance injectors equals the resistance of the resistor that you need. Please someone correct me if im wrong.
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Old 03-12-2008, 02:38 AM   #3
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Some honda's and DSM's have them from the factory so you can check local junk yards. All you're doing is putting a resistor in serious with the injector, not complicated.
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Old 03-12-2008, 04:25 AM   #4
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radioshack idea sounds good to me. any confirmation that it will work before i fry my megasquirt?
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Old 03-12-2008, 04:53 AM   #5
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Your MS should be able to run low impedance injectors.

Meaning, you don't need resistor packs
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Old 03-12-2008, 05:25 AM   #6
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You do need additional grounding though, IIRC. Why are you trying to run low-imp injectors, though?
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Old 03-12-2008, 08:22 AM   #7
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Quote:
Originally Posted by wes65 View Post
are you just trying to turn a low impedance injector into high impedance? If so, you can just buy a resistor from radio shack with the correct ohms. Like resistance of a miata injector minus resistance of low impedance injectors equals the resistance of the resistor that you need. Please someone correct me if im wrong.
You'll need the 10ohm, 10 watt resistors and a really good heat sink.

Or JGStools sells the 4 resistors for ~$20.00, or you can order them for around $3.70ea from mouser. Or you can pull a resistor pack out of a Honda...Or if you have MS, you may or may not need them at all... My low Z's are running just fine on the base MS...
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Old 03-12-2008, 08:26 AM   #8
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if you need to run resistors and dont want to just take someones word for it, here is the info you are looking for to explain why you would use a certain ohm or watt. Also a calculator to help you figure it out.

http://www.injector-rehab.com/kbse/resistor.htm
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Old 03-12-2008, 08:30 AM   #9
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if you are looking into resistors , you should look into running an AEM Injector driver. much better than the bandaid that are resistors...
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Old 03-12-2008, 11:18 AM   #10
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RUN THEM LOW IMPEDANCE!!

at most you have to run a few wires. DO IT. I'll send you wire.
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Old 03-12-2008, 11:43 AM   #11
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http://www.radioshack.com/product/in...entPage=search

I believe this is what you need... its been awhile but I've done this dozens of times. Never added heatsinks and never had any issues. Last car I made a resistor pack for was an MR2 Turbo, I put about 20k on it, and then another 5k or so was put on it before the douche that bought it from me wrapped it around a tree. So they work without issues.

I had planned on doing this with my MS and the injectors I have to eliminate the variable of grounding problems while I tune. And after I get everything setup the way I like it start to screw around with running them low impedance with the MS...

And on that note: Can I get away with installing a single resistor on each of the two injector wires on my "boomslang" or is it necessary to run a resistor for each injector after the wires split?
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Old 03-12-2008, 11:55 AM   #12
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boomslang is the ground...wont help you there.
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Old 03-12-2008, 12:04 PM   #13
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Ah, ****. Now I feel like a doofus. Switched ground, constant power... brain fart.
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Old 03-12-2008, 12:55 PM   #14
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Actually, you could put a single resistor in the harness between each pair of injectors and the MS. You just need to adjust the values.

First, Ohm's Law: I = E / R, where I is current, E is voltage, R is resistance.

Take a simple scenario: If you have a ten ohm resistor in series with a two ohm injector, and you are applying 14 volts, then the current through the system is 1.17 amps. It's actually the current that we're striving for. I don't know if 1.17 amps is "ideal" or not for any given injector, but we'll say it is. Also, we'll note that 13.6 watts are being dissipated as heat in the resistor whenever the circuit it on, so it'll need to be rated for this. (You can get away with a 10 watt part since DC is never 100%, power averages over time in these circumstances)

For two injectors then, first do a parallel resistance calculation, using 1/RT = 1/R1 + 1/R2... Two 2 ohm resistors, in parallel, are an effective 1 ohm load. If we put a 5 ohm resistor in series with the two injector tied together, we have a 6 ohm total resistance. Run the math again, and we have 2.33 amps total through the circuit. However, since the two injectors are of equal resistance, the current will be split evenly between them- 1.17 amps through each. Perfect. Now, however, you've got 27 watts going to heat in the resistor, so you'll need to up-size accordingly- 20 or 25 watts should do in practice.

Alternately, there is a way you could use 10 ohm, 10 watt resistors. Wire two of them together in parallel to form an 5 ohm, 20 watt equivalent resistor pack, and put the resultant resistor pack in series with the line between the injectors and the MS.

All that being said, allow me to reiterate what others have asked. Is there a reason you're not using the PWM driver on the MS to run them as low-impedance injectors? There is a reason they are designed that way; when using a series resistor you lose the benefit of the ultra-fast opening time that low-z injectors are designed to provide.

edit If grounding is that much of a worry, you could always run a pair of heavy (16 ga or so) wires directly from the ground side of R37/R38 to a dedicated ground.
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Old 03-12-2008, 01:23 PM   #15
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mspnp doesnt have board for low impedance injectors...
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Old 03-12-2008, 01:27 PM   #16
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Yes it does. They just don't recommend it because it doesn't come with overbuilt grounds to make sure that there are no noise issues. Ask them how to add more grounds to the MSPNP or do a search on here, they described how to do it at least twice already. Then run those individual ground wires straight to the stock ECU gnd location to help eliminate noise.
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Old 03-12-2008, 01:29 PM   #17
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hm... ok... ill try that then
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Old 03-12-2008, 02:03 PM   #18
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You should be ok. MSPNP is based on the 3.57 SMD MS board, with the extra daughterboard to make it PNP. All the mods you'll be doing will be to the main board, and even though it's primarily surface-mount, the components of interest here are still through-hole.

It just won't work with HR code.
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Old 03-12-2008, 03:14 PM   #19
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any links for write up? i cant find any for some reason. im slow today.
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Old 03-12-2008, 03:26 PM   #20
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Writeup?

1: Solder a big, heavy wire to the terminal of R37 and R38 which is connected to ground.

2: Install a ring terminal on the other end of these wires and connect them to ground at the head.
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