Subaru Justy on megasquirt?

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austynn2001
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Subaru Justy on megasquirt?

Post by austynn2001 »

Hey all, I have an 89 Justy that I recently picked up for the wife. It was carbureted from the factory but I bought a brand new EFI head and intake for it. My plan was to adapt a Harley CV carb, which I did. However, I cannot get it to run right. Now I'm thinking I would be wiser to reinstall the injectors I pulled out and find a throttle body and run megasquirt on her. I've got a couple questions though. First is does anyone know if the justy TPS would be usable by the megasquirt? Also the distributor has no vacuum advance and the only two wires are for the crank position sensor. I believe this one is a 3 tooth which seems like it would be compatible. I'm completely new to the whole world of tuning so please be easy on me :)
jacky4566
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Re: Subaru Justy on megasquirt?

Post by jacky4566 »

What is the voltage output on the TPS sensor? If its a linear 0-5v when you move the throttle then its usable by MS.

You could leave the distributor ignition for now and do Fuel only. or start reading about coil control in the MS manuals.

Two wires means the sensor is a VR. If your not sharing the VR sensor then it will be easy to hookup.

My best recommendation is to start reading the manuals, there are 3. Setup up, Hardware, and Tuner studio.
austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

Thank you for the response. I'm not sure what the TPS puts out for voltage. I'll have to look into that. I haven't purchased one yet in case it won't work. I did see something about using the MS for fuel only at first. I think that would help me get this thing on the road. I will definitely look into the manuals you speak of. I'm very interested in being able to figure out the tuning side of things. I'm very capable of doing any mechanical work but I suck with electronics.
austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

It looks like the Justy TPS just runs off of whether or not there's resistance across the TPS based on position. Does anyone know of a similarly sized (for 1.2L engine) Throttle body/TPS setup I could adapt to my intake that would be compatible with MS?
billr
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Re: Subaru Justy on megasquirt?

Post by billr »

If it is only a variable resistor, not a pot, you could probably get by using it by adding a resistor in series and making it into a pot. It would be quite "non-linear", but should be good enough to define idle, flood-clear, TP-based AE, things like that for a speed-density system. An alpha-n or ITB system... not good.

Honestly, I'm kind of confused about what this TPS is from. You started with a Subaru carb (no TPS?), then talked a about a Harley carb (still no TPS?) and are now asking about a Subaru TPS. Please clarify.
austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

I had mentioned purchasing a throttle body from an EFI Justy and was wondering how the stock TPS would work. I have no clue what the entire first half of your post means but now I've got something to research. Thank you.
billr
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Re: Subaru Justy on megasquirt?

Post by billr »

Okay, let's start with the basics. Do you know what an electrical "pot" (short for "potentiometer") is? If not, focus on studying what a pot is and how they operate; it is a fairly simple but widely-used device. Does the term "variable resistor" mean anything to you?

Did you mention what year and engine (if there were options) that Justy TB/TPS came from? If so, point me to the date of your post with that, I browsed this thread again but couldn't find it. If I can idnetify what that TPS is, it should be easier to advise you on how to use it.
austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

Sorry, I didn't realize pot was short for anything. Yes I know what a potentiometer is. Variable resistor not so much. The throttle body I would ideally use would be from a 94 Subaru Justy. It's a 1.2l 3 cylinder. Weird little thing.
billr
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Re: Subaru Justy on megasquirt?

Post by billr »

Well, I think we have been wandering in the weeds here. I peeked at pictures of that '94 Justy TPS, it has three terminals and is probably a pot like most others. It likely will work fine as-is.

A "variable resistor" is what you would have if you connect to only one "end" of the pot and its wiper, leaving the other end terminal of the pot unconnected. Resistance between the two wires (wiper and one end) would vary from 0 ohms to the full (end-to-end) nominal resistance of the pot as the pot is adjusted.
austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

Ok I ordered a throttle body with the TPS attached. I'll look for a pigtail to fit to make it easier to wire up. So, for sensors all I've got right now will be the two wires off the distributor (crank position), TPS, one coolant temp sensor, one wire oil pressure sensor and a one wire o2 sensor. I have a feeling I'll be needing to upgrade at least a couple of those. It's been a crazy four day weekend but I plan to read through the manuals mentioned above during the week.
billr
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Re: Subaru Justy on megasquirt?

Post by billr »

The oil pressure sensor is non-essential, I wouldn't even try connecting it until the engine is up-and-running fairly well; no need to make the install more complicated than it needs to be at the beginning. The 1-wire O2 sensor is a "narrow band" and really near-useless for tuning; I wouldn't bother to ever connect that.

You do need a MAP sensor and MAT sensor input right at the beginning. The MAP sensor is essential, but the MAT could be "faked" with a simple resistor across that input.
austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

I'd assume a GM MAP sensor would be easiest to use? They're pretty cheap on eBay. And should I purchase the MS3 as well as the relay box?
billr
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Re: Subaru Justy on megasquirt?

Post by billr »

Well, I gave you a bit of bum info on the MAP. You do need that, of course, but the MS has a usable one already built-in! I like using an external MAP sensor (yes, the GM type) so I can have a baro sensor too, and so I don't have to run a long vacuum hose from the engine to where my MS is mounted, and because the external 1-bar sensor gives better resolution on my NA engine. But, that (a MAP sensor) doesn't need to be an immediate buy.

Are you asking about MS3 vs. MS2 or Microsquirt or other? Yes, I always recommend starting with the MS3, and the kit if you have, or are willing to learn, soldering skills.

The relay panel might be handy, but also isn't essential. This was originally a carbed car, right? That probably doesn't have most (any?) of the relays and fuses you will want, so I'm thinking I would order the relay panel. Again, I would go for the kit. If you need to learn soldering, that relay assembly is a lot more forgiving and would be a good place to practice.

By the way, an external MAP sensor isn't so easy to use unless you also have the MS3X board. The MS3X is also a good value, but doesn't need to be an immediate buy.
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Re: Subaru Justy on megasquirt?

Post by racingmini_mtl »

austynn2001 wrote:And should I purchase the MS3 as well as the relay box?
If you are talking about the Megasquirt relay board, it is definitely not adapted to an MS3 setup so I would not use it but would rather start from a generic automotive unit.

Jean
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austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

You are an awesome help. I don't mind buying what I have to in order to get this thing running well. I normally would have done some reading by now, but we hit some very serious family troubles this weekend so free time is going to be cut severely. I'd like to collect whatever parts and pieces I should have to be prepared for when I've got time again. It was indeed a carbureted car. I thought I had seen somewhere that MS3 was best for a 3 cylinder engine. I am not opposed to getting the kit and really learning the system. Would I be money ahead just to get the MS3X board right off the bat? I appreciate hearing from someone with experience in a subject who know what to do. However, it's knowing what not to do that usually saves more money.
billr
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Re: Subaru Justy on megasquirt?

Post by billr »

I don't think there is any cost saving by ordering the MS3 and MS3X at the same time. The MS3X is very easy to add later, so i would wait on that until you see if you really need its features.

Without the MS3X, I would do a "standard" build of the MS3 and use its built-in coil driver along with the existing single-coil and dizzy cap/rotor. With a 3-cylinder engine you will probably never run out of dwell time with that single-coil (like I do with a V-8), so there may never be any real advantage to modding the stock MS3 or adding an MS3X so you can use COP or CNP.

Likewise, the standard build only provides two (universal) injector drivers, so you would probably be limited to firing all injectors at once with this 3-cylinder; but that should work fine. If you do decide later that you want full-sequential injection, then the MS3X is the easiest way to get that and the needed CMP input in one easy package. Just be sure to run individual control wires to each injector and join them near the MS, not at the engine. That way they can be split out later for sequential, if desired.

Most (all?) of the MS3X features can be duplicated by adding fairly simple custom circuits to the basic MS3, but pricing on the MS3X is so low it is hardly worth the effort, even for us that are fairly comfy with electronic circuits and design.

I also suggest you buy that "how to" book from DIYautotune. I don't have one, but am probably stupid not to...

A stim (the JimStim only) would be helpful, but not essential. It is another good place to practice your soldering skills, but if money is tight I would spend the dollars on the relay panel, not the JimStim.

Keep asking questions, our goal here is to help you have a satisfying experience with MS. Listen, at least, to others if they differ from my opinions, I am not claiming to be infallible!
austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

I'll order an MS3 and the relay box on Friday. I'll do as much reading as I can fit in in the meantime. Do you think it would be worthwhile to get a GM MAP sensor coming as well? I don't mind investing early to save myself headaches in the future.
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Re: Subaru Justy on megasquirt?

Post by jsmcortina »

As Jean says, avoid the "Relay board".

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WestfieldMX5
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Re: Subaru Justy on megasquirt?

Post by WestfieldMX5 »

no need for the GM map sensor. There's a map sensor inside the MS3 that works just fine.
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austynn2001
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Re: Subaru Justy on megasquirt?

Post by austynn2001 »

jsmcortina wrote:As Jean says, avoid the "Relay board".

James
Thank you. Somehow, I never even saw his post there. Forums suck to use on this phone. So I'll pick up the MS3 kit as well as the JimStim kit. Will the crank position sensor within the distributor be sufficient or will I need trigger wheels for the crank and/or cam?
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