I'm confused about injector banking, timing....oh and alternating injection - Miata Turbo Forum - Boost cars, acquire cats.

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Old 08-29-2008, 04:29 PM   #1
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Default I'm confused about injector banking, timing....oh and alternating injection

I noticed that the Megamanual doesnít say anything about timing when running fuel only, it seems like it only needs RPM.

I always thought that MS needed to know when to inject based on crank position but Iím starting to think that it doesnít (unless youíre running sequential injection).

The reason I mention it is that I have no way to determine what my CAS is set at since Iím not running spark yet and itís a í99.

Iím wiring up my injectors now, and Iím going to go with 2&4 and 1&3 banking, but I wonder if it matters?

For that matter, why use alternating injection instead of simultaneous injection?
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Old 08-29-2008, 06:16 PM   #2
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It won't matter how you pair your injectors. I did mine 1&2, 3&4 I think. It won't make any difference. MSI can not run sequential injection. MS2 can, but you would need a crank and cam sensor for the MS to distinguish TDC on the compression stroke from TDC of the exhaust stroke. Sequential injection is mainly used to 'slightly' increase fuel economy and emissions. Basically forget about it. I think I use alternating injection but can't remember. The why is so you don't open all the injectors at the same time and then fuel pressure drop at the same time. By staggering them it helps reduce the pressure drop.
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Old 08-29-2008, 07:03 PM   #3
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Ive read that it makes a difference in idle quality and part throttle driving. It may not have an effect on power production but I've read that it has an effect on the quality or driveablility of the car. I paired mine according to how the coil packs are paired.
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Old 08-29-2008, 08:47 PM   #4
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Originally Posted by RdSnake View Post
Ive read that it makes a difference in idle quality and part throttle driving.
That's exactly it. The move from banked to full-sequential was done primarily to reduce emissions at idle and light throttle. Under heavy throttle, the injectors are, by definition, all running pretty much all the time. Think of it this way: the intake valve only does about 30% duty cycle, yet the injectors are commonly run all the way to 80 or 90% duty cycle. IOW- at heavy load, the injectors are shooting at a closed valve most of the time anyway.

The official injector pairing is 1-3, 2-4. This is different from the ignition pairing.

Fluke, the MS does know when to inject based on crank position. You don't get to specify the injector timing, it's automatic. You can not easily determine whether your injectors are 180 degrees out of phase without access to an oscilloscope, and truthfully, it doesn't really matter all that much. If your wheel decoder is set up correctly, then INJ1 is 1-3, and INJ2 is 2-4.

Last edited by Joe Perez; 08-30-2008 at 12:16 AM.
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Old 08-29-2008, 09:32 PM   #5
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The official injector pairing is 1-3, 2-4. This is different from the ignition pairing.

You mean OEM wiring? I believe it is. But I remember reading a thread on the MS Board, when I was setting up my MS-II early last year, that made me pair the injectors the same way the ignition wires are paired.
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Old 08-30-2008, 12:27 AM   #6
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Yes, the OEM pairing from '90-'93 was 1/3, 2/4. Attached below is an excerpt from the '92 FSM. As has been said however, its not a matter of life or death, merely an emissions thing. This is why the '93 CA model was the first Miata to get full sequential injection, (it had a completely unique ECU and harness) whereas the rest of the cars didn't get it until '94 with the change to the 1.8 engine.

When I first did mine, I accidentally had the two injector lines reversed, and it made very little perceptible difference when I corrected the wiring later.



FWIW, the first-gen port injected 4 cyl engines from Toyota and Mitsu also use the same injector pairing. Not sure about Honda.
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Old 08-30-2008, 09:55 AM   #7
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Thanks a lot Joe. Would you be able to post your timing settings? I'd like to at least have something reasonable in there.

Thanks again!
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Old 08-30-2008, 11:29 AM   #8
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Quote:
Originally Posted by fluke View Post
Thanks a lot Joe. Would you be able to post your timing settings? I'd like to at least have something reasonable in there.
Before I removed my CAS, I used the default DIY wheel configuration. Assuming an NA CAS, the following settings will be correct assuming that you are wired for INJ1 to drive 1&3, INJ2 to drive 2&4, SparkA to drive 2&3, and SparkB to drive 1&4. Also, this is for MS1. The MS2 setup screen is different.

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Old 08-30-2008, 02:27 PM   #9
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I was going to follow the OEM injector wiring but my research on MSEFI made me conclude to follow the firing order.
Read the post by devastator about 5th post from the bottom:


http://www.msefi.com/viewtopic.php?f...57852f#p201671
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Old 08-31-2008, 08:52 AM   #10
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Originally Posted by Joe Perez View Post
Before I removed my CAS, I used the default DIY wheel configuration. Assuming an NA CAS, the following settings will be correct assuming that you are wired for INJ1 to drive 1&3, INJ2 to drive 2&4, SparkA to drive 2&3, and SparkB to drive 1&4. Also, this is for MS1. The MS2 setup screen is different.

Thanks Joe, could I see what you had for the data on the "spark settings" page?
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Old 08-31-2008, 12:15 PM   #11
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I don't have a copy of that page available right now- I'm away from home using a laptop and just happened to get lucky that my wheel settings were already posted elsewhere.

Basically, it's just the defaults, I think my trigger angle was about 70, and I set a cranking advance of 15. It's been a while since I looked at that screen, so I'm going from memory. Your settings will vary.
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Old 08-31-2008, 12:22 PM   #12
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Quote:
Originally Posted by RdSnake View Post
I was going to follow the OEM injector wiring but my research on MSEFI made me conclude to follow the firing order
Yeah, I saw that. And I went through a basically similar thought process early on while deciding how to wire the car. My experimentation produced similar results to his, in that "changing the injector leads from injector to injector, had very little effect."

Ultimately, I decided to set them up in the same order that they were configured from the factory, under the assumption that someone at Mazda who knows more than I do about engine management decided that they should be that way for a reason. From time to time, I find it easiest to simply humble myself and accept certain things as articles of faith.
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Old 08-31-2008, 12:40 PM   #13
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Quote:
Originally Posted by Joe Perez View Post
under the assumption that someone at Mazda who knows more than I do about engine management decided that they should be that way for a reason.
Meh, maybe. But there are a lot of shortcomings from Mazda too like the thermostat position for example. But yeah I see the point I guess. But anyways my car idles at 700 RPM cold just fine.
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Old 08-31-2008, 01:37 PM   #14
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Thermostat position... no ****. Living in SoCal for years, I never understood what the big deal was- my engine never overheated, even on the massive canyon runs we'd do a couple times a year. As soon as I got to FL, the needle started spending most of its time fluctuating between the 1 and 2 o'clock positions as the fans fought to keep up... I gotta do a reroute if I'm gonna be staying around here.

But yes, I was surprised as I played with it how little it seemed to matter in which order the injectors were wired. I figured that since I was making a pseudo-arbitrary decision, I might as well rely on precedent and go with how it'd been for years.
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Old 08-31-2008, 01:41 PM   #15
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The original injector pairing may be good with the original ecu but may not necessarily be good with megasquirt. Anyway, the difference may be purely technical and may not matter at all in real life. I just wanted to substantiate the reason why I did mine using the firing order.
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