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:
This will be the third MS that I've tuned, so I'm not a total newb. Just second-guessing myself a bit. |
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. |
#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. |
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 |
yes, use the writeup Frank (and I*) have out there.
*I say I because I contributed to it. |
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... |
there's the purge valve, or there's probably two more in the AFM harness you could use.
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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... |
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. |
Originally Posted by Loren
(Post 949267)
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)
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. |
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. |
Originally Posted by Loren
(Post 949281)
But, if you guys think I absolutely don't need to worry about that... I'll trust you. :)
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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. |
1D is a ground. 1F and 1K could work. 2P 2O and 2K should all work off the AFM.
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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. |
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. |
Originally Posted by Loren
(Post 951035)
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.
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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. |
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? |
1 Attachment(s)
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: https://www.miataturbo.net/attachmen...ine=1353361820 |
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