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Old 02-05-2008, 09:07 AM   #1
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Default Standalone MS install on a 94

I'm midway through my MegaSquirt setup. I've been heavily noting everything I do on the way, but I'm now coming to a few points of contention, primarily because I'm doing this as a standalone ECU in the factory case.

I was wondering, has anyone done a standalone install of a DIY MS in their MX-5 (ie, MegaSquirtPNP does not count), and how did you solve things such as where to wire the AC? What should I do with the many other seemingly unused wires in the harness?

I'm pouring over a few wiring diagrams now and seeing what I can figure out, but if anyone has pointers then I'd appreciate the help.

Thanks.
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Old 02-05-2008, 10:00 AM   #2
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It's never been done and there's nowhere you can find info.


especially not here -------V
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Old 02-05-2008, 10:11 AM   #3
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Sorry mate, we all buy MSPNP's.
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Old 02-05-2008, 10:13 AM   #4
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Wow really? Jeez.

Looks like I've got some unexplored territory to wander through.
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Old 02-05-2008, 10:24 AM   #5
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Wow really? Jeez.

Looks like I've got some unexplored territory to wander through.
They are being sarcastic. A bunch of people have DIY MS's installed on 94's.

Including myself.

I have no A/C so I can't help you there.
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Old 02-05-2008, 10:29 AM   #6
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Old 02-05-2008, 10:35 AM   #7
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He had proper grammar, even if the question has been repeated a million times, and he should have searched before, he deserved at least one proper answer.
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Old 02-05-2008, 11:00 AM   #8
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Originally Posted by reddroptop View Post
He had proper grammar, even if the question has been repeated a million times, and he should have searched before, he
deserved at least one proper answer.
if standalone and megasquirt was searched, my stick post would have been the first thread linked.

without hazing miataturbo.net is just a big circle jerk.
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Standalone MS install on a 94-bingo.jpg  
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Old 02-05-2008, 11:24 AM   #9
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if standalone and megasquirt was searched, my stick post would have been the first thread linked.

without hazing miataturbo.net is just a big circle jerk.
My post was thinly-veiled sarcasm. Your thread is not relevant to my question. Has anyone DIY'd the MS in their 94, and kept their air conditioning. What of the other unused wires - did you find a use for those?

Your thread makes no mention of AC. Posters in your thread basically kissed their AC goodbye or never had it in the first place. I'm still wondering - does the ECU ground that wire under particular circumstances? Is it always grounded? Is it just a sense wire to tell the ECU when the AC is on?? But, thanks for assuming I'm an idiot. I've searched with many keywords, both forum-specific, msefi, miata.net and Google, but I'm not coming up with much.

I have figured most of the wiring myself thanks to some diagrams from my Haynes manual and a harness diagram from DIYAutoTune. I just can't figure out how the ECU is relevant to the operation of the air conditioning.

* From what I understand of the AC condensor fan, that only operates when the factory ECU reads a temperature from the above a certain temperature level - otherwise it is activated by the AC relays - hence it has a wire to the ECU.
* The coolant fan relay is an easy fix - I can wire that with no problems, or just use the existing voltage switch I have now.
* Clutch switch - I've found the wire, I'll just have to patch that in for use with the launch control once that's hooked up
* (and more when I think of it when it's not 1:30am in the morning)
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Old 02-05-2008, 11:25 AM   #10
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to be fair, the HOWTO doesn't cover things like A/C, and is fairly piggyback centric.

Sabre - If you look over the factory wiring diagrams, it's fairly obvious how to enable the factory A/C without the OE ECU. A few relays on a separate board will do it. The tricky stuff comes with adjusting the idle when the A/C is on, and shutting off the A/C at WOT.

I'm working on an MS2 for my 94, hoping it will eventually be standalone. I've got other issues on the table now, but I hope to eventually address the A/C topic.
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Old 02-05-2008, 11:32 AM   #11
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Thanks beer! The FAQ is very piggyback centric. When I bought my car, it came with the Haltech E6A fit already - so I don't have a factory ECU. The MX-5 ECU I do have is one I bought from a local disassembler for $20.

One thing I've also considered so far is where the AC goes into on my current Haltech setup - which will require a multimeter and the pinout of the E6A's harness (which I also have). The ultimate goal for me is to have the MS in the factory case, which is going to require a bit of grinder work, some spacers and some careful positioning. The MAP sensor will either be relocated externally, or I'll just drill a hole in the case for the MAP vacuum tube to go into. I'm suspecting it's either just not connected or grounded.

I've got a lot of it figured out but won't fit it into the MX-5 ECU case until I've tested the MegaSquirt thoroughly. No point going to the effort of that if I just throw in the towel in frustration anyway.

But right now I'm up to the part where I'm soldering the DB37->MX-5 adaptor harness together, hence my current question regarding the AC and any other wires people found to be of interest.
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Old 02-05-2008, 11:35 AM   #12
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I didnt see the a/c part.

no if you run piggyback you'll have to built a custom circuit to engage the a/c. Diyautotune.com did this with the MSPNP, which was the only reason it took them so long to come out with it.

It wont hurt you to run piggyback and only have the oem ecu control it and nothing else.


while the I only have a 92 shop manual, the circutry should be the same for your 94, just the wires at the harness wont match, so this should help you figure out what you need to do. I want to figure it ou one day, but i got too many other things i gotta do.

http://www.boostedmiata.com/pdfs/

please save as.
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Old 02-05-2008, 07:46 PM   #13
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I'm running home built MS on a 1995 full standalone and my attack plan for A/C is pretty simple.

Already wired the aux A/C cooling fan relay trigger in with the main cooling fan, so they both run when needed.

Haven't tested this part yet, but its pretty simple for me. I'm simply removing the PCM from the equation 100% because I didn't think it was really necessary to screw with. Going to attach the wiring diagram also, but its pretty simple.

Theres +12 volts going to the fan/ac switch on your dash, which runs into the evap core temp switch, then into the system pressure switch, finally into the PCM. PCM takes that signal into account, along with throttle position/engine load then decided if its prudent to allow the AC to run. When the temp reaches a specific set point inside the evap, it'll kill the compressor clutch. All the PCM does is ground the relay for the compressor clutch when its time for action, so I'm going to add in a relay to take place of the PCM.

Theres a blue/black wire that goes from the clutch relay to the PCM on connector 1J. As said before, the PCM just grounds that. Hook that to a relay, input of the relay would be just ground.

Typical Siemens/Tyco relay wiring would be this:


So I'd ground Pin 30 and 86 to the chassis/engine.
87 You would wire to the blue/black wire.
85 you'd wire PCM 1Q which is Light Green/Black wire coming from the dash switch, pressure switch, and temp switch.

I'd check all this out before you actually try it, which is what I'll be doing here in a week or two if it warms up. By theory of the wiring diagram, turning your A/C Switch on, if the core temp and pressure are correct you'd send a +12 volts to the relay, which would ground the clutch relay, and boom.. A/C. This will not cut off the compressor for full throttle acceleration, but that I don't care about. I don't use the A/C very often, normally when sitting in traffic or waiting at autox on a hella hot day.


This is the 1995 A/C wiring diagram, which is the same as 1994.
http://www.jugrnot.com/95sys-1.jpg (HUGE IMAGE!!)

Good luck!
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Old 02-05-2008, 08:10 PM   #14
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I am running MS-II v3.0, EDIS with IRTB's. I did a parallel install on my MS. The MS controls fuel and spark while the factory ecu controls idle. It works quite well. I get idle up when I press the a/c switch, turn the steering wheel and warmup-all the nice qualities of factory idle. I think its the perfect combination. I let the factory ecu handle idle and I let MS handle spark and fuel.
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Old 02-05-2008, 08:36 PM   #15
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Quote:
Originally Posted by elesjuan View Post

Already wired the aux A/C cooling fan relay trigger in with the main cooling fan, so they both run when needed.

How did you do this, I want to get my AC fan to turn on with the radiator fan.
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Old 02-05-2008, 08:43 PM   #16
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How did you do this, I want to get my AC fan to turn on with the radiator fan.
What hole have you been hiding in? Just jumper the two wires on your boomslang that go to the fans. That will trigger both relays so both fans come on at the same time.
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Old 02-05-2008, 08:52 PM   #17
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What hole have you been hiding in? Just jumper the two wires on your boomslang that go to the fans. That will trigger both relays so both fans come on at the same time.
LOL!!!

Yeah, jumper boomslang pins 1L and 2S to your fan output mod on the megasquizzle.
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Old 02-05-2008, 08:54 PM   #18
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elesjuan - that's about what i thought was involved. from the factory wiring diagrams, it appears there's a switch as well as variable resistor on the TPS, i'm wondering if that's a WOT or closed switch. that might help in the WOT declutch. what are you doing about idle control with A/C on?
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Old 02-05-2008, 09:27 PM   #19
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Haven't gotten that far yet. I have about 6 hours total driving and tuning time, I'm really comfortable with the tune as it sits now. Have made several WOT redline pulls in 1st, 2nd, and thrid gears keeping a close eye on AFR with great success.

The circuit I described isn't final, I haven't even started to build it yet. For A/C Idle, I'm not 100% sure. Kinda wish I knew exactly what DIY did for A/C but I'm not too worried about it. Maybe with a good enough tune MS can handle the extra drag on the engine by increasing the idle pulse and maybe a little more fuel? We'll see.

I also noticed theres an "idle switch" output from our TPS (Red wire, goes to position 1N on PCM) but it almost appears its a normally open circuit, so I assume its a WOT switch. From what I can tell, it gives a +5 volt feedback when the circuit is closed returning to the PCM but I've yet to test it. If thats the case, I might include that to kill my A/C clutch relay circuit when I hit wide open. Was just planning on turning it off manually when needed.

Not really sure how far along you are with the project but I'll offer up any documentation I've taken during this if it'll help you. I've got the wiring diagram (easy to find though) for the entire cars electrical systems, mapped the pinout of the PCM harness to interface with Megasquirt, etc. Are you building the boomslang harness to do a full plug-n-play with wiring?

http://spreadsheets.google.com/pub?k...A0Z3FkV_q0Wjbg

Thats my spreadsheet with pinouts. The clutch switch doesn't currently work for launch control, don't know if you're planning on that or not. If you have cruise control that switch on the clutch is wired in parallel with the brake pedal switch to shut down cruise when you depress the clutch or brake pedal. Using that switch for launch control trigger, I'm in launch mode 100% of the time because the circuit isn't an on/off. Going to mount my own microswitch on the clutch pedal for launch with an arming switch. Other things like 1E (Check engine light) I've wired up for shift light, reusing the PRC valve wiring harness for my boost control solenoid to keep from running more wires, and a 94 you shouldn't have to worry about the tach output mod from megasquirt. Your coil harness should have 5 pins total. +12, GND, Trigger1, Trigger2, Tach. All the extra inputs and outputs I'm planning on using in the future I went ahead and added an aux i/o DB15 plug in place of where the LEDs would be, so that helps a lot when all 37 pins on your DB37 are used up.

Anything else you need some help with, feel free to ask and I'll do my best! This thing is a total freaking blast to play with!
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Old 02-05-2008, 10:18 PM   #20
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Quote:
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LOL!!!

Yeah, jumper boomslang pins 1L and 2S to your fan output mod on the megasquizzle.
Looks like 1a and 1b on my car according to madracki diagrams.
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