550cc low impedance..help - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-18-2007, 05:52 PM   #1
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Default 550cc low impedance..help

okay..i read the manual but didn't quite get it.... my injectors are 550cc low impedance...i'm on constant page 1 and set my fuel requirement engine displacement at 1599cc and dail 550cc for injectors size and 14.7 for air fuel ratio..and caculated out a 4.9 / 4.9 ....what do i set my PWM current limit at? and my PWM time threshold (ms) ? any help? i'm lost...anyone running the same setup?
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Old 10-18-2007, 07:22 PM   #2
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Do a search for "low impedance" then read all the threads in the megasquirt subforum. You questions are answered there.

If you are using the PNP I strongly suggest you use resistors inline with your low z injectors. The Low z injectors sink alot of power to ground and the PNP doesn't have sufficient grounding in original form to support them. So basically it can be done, but it won't be easy and adding resistors will make your life a whole lot better.

The PWM settings you need are listed in the forum and in the megamanual.
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Old 10-18-2007, 07:29 PM   #3
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is there a site where i can learn how to put on a resistor? because i don't even know what that is...not too smart about these things..thats why i'm here...
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Old 10-18-2007, 08:54 PM   #4
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There are resistor packs on a ton of cars from the factory, I know alot of late 80's Toyota's use them. They're often in aluminum cases, maybe about the size of a pack of cigarettes, sometimes with fins like a heatsink. The MegaManual covers alot of this (www.megamanual.com), but basically you wire it in so your low impedance (2-6 ohm) injectors are seen by the ECU as high impedance injectors (12-16 ohm). The add resistance and sink away the heat...
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Old 10-18-2007, 09:03 PM   #5
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It seems to me that low-z injectors just aren't worth the hassle. Sell them, get a set of high-z Rx7 550ccs, and plug them right in.
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Old 10-18-2007, 09:09 PM   #6
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That's definitely the easiest solution....
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Old 10-19-2007, 11:36 PM   #7
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I opted for the $30.00 flyback board for my MS1-V2.2, that will allow you to run low-z injectors without resistors.

http://www.diyautotune.com/catalog/m...ecus-p-44.html
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Old 10-19-2007, 11:41 PM   #8
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Are you currently running the low z injectors with no problems?
The people that have had problems have been running the V3 board with the built in flyback. Only reason why i ask.
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Old 10-20-2007, 04:07 AM   #9
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Quote:
Originally Posted by cjernigan View Post
Are you currently running the low z injectors with no problems?
The people that have had problems have been running the V3 board with the built in flyback. Only reason why i ask.
So far so good.. Not saying much for it, I think I've got like maybe 20 miles on it.. lol.
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Old 10-20-2007, 09:24 AM   #10
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The v2.2 with flyback board, and better yet the v3.0 board, absolutely will run low impedance injectors with no problem. Using the stock grounds in the Miata becomes the limitation very quickly and I suspect is why many have had issues on these cars. I don't see these issues on other cars with dedicated grounds and proper wiring, including big nasty twin turbo V8's with 160lb low-z injectors...
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Old 10-27-2007, 06:26 PM   #11
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Just get the high Zs because I got mine to run fine except cutting out at random times. I added tons of grounds but nothing worked?? Put the 550 high Zs in and no more problems.
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