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Old 11-11-2012, 11:44 PM   #1
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Default Doing MS3x on a stock 91

So, I bought a MS3x with a DIYBOB from a member here. Should have it in my hands next week. Trying to be ready to plug it in and start playing ASAP.

The unit in question was set up for and installed in a '94. So, I'm looking to do whatever mods I need to do to convert it from '94 spec to 90-93 spec.

Studying the ECU pinouts between the two cars, since the 94 wasn't really all that different electrically, it appears that the only thing I'll have to change is the cooling fan output from pin 1L to pin 1R.

My first goal is just to get the car running on the MS with the stock AFM in place (I know I'll only really be using it for the AIT and to turn on the fuel pump). I want to see how much difference can be made strictly with tuning. Then I'll remove that AFM and play with sequential injection... and whatever else I feel like doing.

QUESTIONS:
  1. Is the above assumption about 94 to 90-93 wiring differences correct?
  2. There's some "fuel pump mod" that I can obviously avoid doing by just jumpering the fuel pump... is there any reason to consider DOING this mod? What's the benefit? (bearing in mind that I hypermile in this car, and frequently engine-off coast with the ignition on)
  3. I know on the MS2 there is a recommended ignition output mod to keep from frying coils... and I know that the MS3x uses it's own on-board outputs. What's the status of that default high ignition output on the MS3? Is that mod required, or is it a non-issue?
  4. The diode has been added to the IAC circuit on the DIYBOB. Any other similar Miata-specific mods recommended?
  5. Please point me toward the best MS3x write-ups out there. I've found some of them, but which one is best? Idunno.
  6. Any other tips that you think might help.

This will be the third MS that I've tuned, so I'm not a total newb. Just second-guessing myself a bit.
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Old 11-13-2012, 02:05 AM   #2
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Working on answering some of my own questions, might as well document here.

#2 - Fuel Pump
When I remove the AFM, I'll wire this output to Pin 2o on the stock harness. This will send the FP switching ground from the MS through the unused AFM signal wire. Then, I'll jumper pins A & F on the AFM connector, which will send the ground to the Fuel Pump Relay. Simple. No added wires. Easy to revert to stock. I like it.

Last edited by Loren; 11-18-2012 at 04:23 PM.
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Old 11-13-2012, 02:52 AM   #3
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#3 - Ignition Output default state
In the thread about the output inversion mod, I found it was stated (by both Matt & Joe) that the mod is not required for the Microsquirt (and Micro based PNP) because those units use a low-current logic-level output, which should be low, anyway. Since the MS3x uses the same type of logic-level output, I'm going to assume that the same applies. No danger of burning out igniters or whatever due to a default high-current output being applied at power-up.
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Old 11-13-2012, 04:26 AM   #4
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might help. used it to build my own ms3x (although I haven't got my car started with it yet...)

90-97 MS3 with MS3X | My Westfield MX5 90-97 MS3 with MS3X | & Megasquirt site
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Old 11-13-2012, 09:18 AM   #5
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yes, use the writeup Frank (and I*) have out there.



*I say I because I contributed to it.
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Old 11-13-2012, 11:58 AM   #6
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Okay, cool. Just read over that one. Pretty straight forward. Funny that I came up with exactly the same method for the FP switching. Must be the right thing to do!

Wish I could find some existing wires to use for sequential injection, but there don't appear to be any good options. Oh, well. First priority is just to get the car up and running on the MS...
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Old 11-13-2012, 12:21 PM   #7
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there's the purge valve, or there's probably two more in the AFM harness you could use.
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Old 11-13-2012, 12:31 PM   #8
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I wanted to leave the purge valve because I read that some people were using it as an additional "idle-up" valve to help with AC idle-droop. (and I have a Fidanza, so that could be an issue)

I did consider the purge valve and the PS pump wire (I have manual steering) as an option. Didn't consider other AFM wires... hmmm...
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Old 11-13-2012, 12:36 PM   #9
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lol. you have a ms3x, that has idle up code bro.

a/c activation is better than stock.


dont read any posts that pertain to a MSI.
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Old 11-13-2012, 12:40 PM   #10
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Quote:
Originally Posted by Loren View Post
I wanted to leave the purge valve because I read that some people were using it as an additional "idle-up" valve to help with AC idle-droop. (and I have a Fidanza, so that could be an issue)
The MS3 actually implements A/C control directly. You wire the A/C switch into an input pin on the ECU, and configure an output pin to drive the A/C relay. When you turn on the A/C, the ECU idles the engine up, waits, and then engages the relay.

It also supports idle-up for the fan output as well.

Very slick.

(Edit: curse you, Braineack, for beating me to the point. Now I look like a Johnny-come-lately. You will rue this day.)


For the sequential conversion, I just ran six new wires (four INJ and two GND) through the little hole in the firewall which is behind the fusebox. Bored it oversize a bit with a unibit, used a wood bit to mangle a hole through the rubber pad behind it, and then used a coat-hanger to pull the new wiring bundle through. Put some split-loom tubing around it, and ran it in parallel with the stock harness that goes up to the back of the head.

Much easier than un-wrapping a bunch of 22 year old harness to sneak one or two wires out of it.
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Old 11-13-2012, 12:54 PM   #11
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Yeah, I'd read about the MS3's great idle control and AC idle-up, and I'll be using it. Just wasn't sure I wouldn't need to do any other tricks, so I was going to leave the purge valve on the table. But, if you guys think I absolutely don't need to worry about that... I'll trust you. And I look forward to being impressed!

I hear ya, Joe. Was thinking of maybe doing something like that... maybe run a dozen "spare wires" through the firewall to cover sequential fuel and anything else that might come up later.

My box is supposed to ship today. I'm gonna be jonesin' all week.
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Old 11-13-2012, 01:06 PM   #12
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Quote:
Originally Posted by Loren View Post
But, if you guys think I absolutely don't need to worry about that... I'll trust you.
You don't need to worry about it. The MS3 does everything except make you a sandwich, and I understand that they have that partially functional in the current Alpha code.
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Old 11-13-2012, 06:29 PM   #13
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Mmmm... sandwiches.

Hey, what about pins 1d, 1f and 1k that go directly to the diagnostic connector that I'm not using? I'll have to check their size, but they could work for injector circuits.
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Old 11-13-2012, 06:52 PM   #14
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1D is a ground. 1F and 1K could work. 2P 2O and 2K should all work off the AFM.

Last edited by Braineack; 11-13-2012 at 07:05 PM.
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Old 11-13-2012, 07:55 PM   #15
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I'm using 2P for the AIT. 2O for FP switching.

Looks like there are a few wires hanging out there that could be used, though. I like repurposing stuff.
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Old 11-18-2012, 06:01 PM   #16
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Update.

For the seq. fuel, I'll be using pins 1F and 1K to the diagnostic connector. I'm trying to retain easy backwards-compatibility with the stock ECU and systems for now, so I'll just tap into those wires and run a 2-wire harness for those two injectors that can be easily unplugged and switched back to stock.

Pretty simple stuff so far.

I also decided to go ahead and order a WB02. Bought one of those $105 units from 14point7.com, we'll see how well it works. I was going to try to tune with the stock NB, but thought better of it.

FedEx says I won't see my MS3 until Friday.
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Old 11-18-2012, 06:50 PM   #17
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Quote:
Originally Posted by Loren View Post
I also decided to go ahead and order a WB02. Bought one of those $105 units from 14point7.com, we'll see how well it works. I was going to try to tune with the stock NB, but thought better of it.
I'm looking forward to your review of this unit. I've read a lot about it, but never actually heard a first-hand account. Hopefully you will retain the stock NBO2 sensor as a calibration reference.
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Old 11-18-2012, 08:22 PM   #18
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Not planning to install a second bung in the exhaust (though... I guess I could).

But, I can easily do some reference tuning and logging with the stock sensor... then switch in the new sensor and log the same points. (all with EGO off, of course) Would be a good reference test in lieu of having both sensors in the system.
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Old 11-19-2012, 05:47 PM   #19
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Hey, is anyone familiar with the stock injector harness? Oh, I bet someone is!

I figured I'd go ahead and pre-configure my injector harness so that I can switch a plug when I'm ready to go sequential.

I know the injector signal wire is shared between pairs of injectors coming out of my ECU... anybody know where they actually split into two wires? Is it right where the harness splits to go to the individual injectors, or is it somewhere before that?
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Old 11-19-2012, 05:48 PM   #20
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it's easy to determine when you rip apart the harness. I cant quite remember off the top of my head.

here it's just around the first injector:

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Doing MS3x on a stock 91-ms3x-051_001.jpg  
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