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420A What is needed for megasquirt?

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Brad Bell

Proven Member
192
5
Aug 15, 2014
Levant, Maine
I have been running a fmu/stock ecu turbo setup for years now and I am ready for megasquirt. Tired of all the bugs/unreliability and really just want to make the jump from one to the other.

I'm new to the whole megasquirt/tuning deal but have been doing alot of research the past couple weeks. So I'm asking what specifically is needed other than the unit itself. I'd like to do a complete standalone system pre assembled, I'm thinking a megasquirt 2 assembled unit from diyautotune.com with a 8' standard harness.

Now to the specific questions I have. Other than the assembled unit and harness, is there anything else I will need to order from diyautotune? Is there any specific mods I have to do to the unit to work correctly? I have read, and seen videos of guys installing megasquirt and they are installing a second coolant and manifold temp sensor, what is the reason for this? Can we not hook up the existing sensors to the ms? Map sensor?

As for fuel, I am running a begi/cartech rising rate sfmu, and understand I will need a 1:1 rising rate regulator instead if I'm correct? What model works best?

Thank you
 
The MS2 and 8’ harness will work. Just let them know what you will be using it on so they can do any internal mods when it’s being built.

I use both the stock coolant temp sensor and manifold air temp sensor. Second coolant temp sensor could be due to them keeping the stock ecu in place. Moving the air temp sensor to the inter cooling piping makes sure the sensor doesn’t get heat soaked like it can in the manifold. I have been meaning to move mine.

Map sensor is on the main board the the MS unit.

Any 1:1 rising rate FPR will work. Obviously go with a more name brand unit like aeromotive, fuelab, etc.

You will also need a wide band air fuel ratio gauge. The output gets sent to the MS unit so it knows what the AFR is.
 
Megasquirt can use pretty much any sensors in existence, but because it is most commonly used on EFI swaps for LSx V8s, the GM style sensors are well documented and come configured by default. To many, swapping sensors is easier than calibrating the existing ones, but its not a big deal. The 4G63 has some pretty decent Megasquirt support these days as well, and I'm considering it for mine because I find it easier to get right than ECMLink, H8 black box, and EVO 8 ECU.

If your engine harness is in good shape, you can get the DIYPNP N76 which is based on the MS2 and comes with the factory connectors for direct plug and play into the existing harness. No wiring necessary, but you can't get them preassembled.

OP has a 420a so that N76 won’t work. Have to do it the hard way on the 420a.

DIYAutoTune's website lists the N76 as compatible with all 2g DSMs regardless of engine option, hence my suggestion, but it's entirely possible they don't realize the 420a exists. I don't have any knowledge of the 420a ECU connectors. EDIT: Oh yeah, no. Completely different connectors. In my search for male 420a connectors to make a patch harness (which I did not find) I did find this: http://old.symtechlabs.com/catalog/complete-420aneon-megasquirt-ems-kit-p-57.html but it still lists the LC-1 as the latest EGO, so who knows if it's still an option.

Edit again. https://www.symtechlabs.com/megasquirt-ems/megasquirt-ems-kits/420a-neon-megasquirt-ems-kit.html Out of stock but potentially worth an email? Still not PnP though. Seems like it's just the normal MS2 stuff plus a 420a alternator voltage regulator, whatever that is supposed to achieve.
 
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Megasquirt can use pretty much any sensors in existence, but because it is most commonly used on EFI swaps for LSx V8s, the GM style sensors are well documented and come configured by default. To many, swapping sensors is easier than calibrating the existing ones, but its not a big deal. The 4G63 has some pretty decent Megasquirt support these days as well, and I'm considering it for mine because I find it easier to get right than ECMLink, H8 black box, and EVO 8 ECU.

If your engine harness is in good shape, you can get the DIYPNP N76 which is based on the MS2 and comes with the factory connectors for direct plug and play into the existing harness. No wiring necessary, but you can't get them preassembled.


OP has a 420a so that N76 won’t work. Have to do it the hard way on the 420a.
 
You will also need a wide band air fuel ratio gauge. The output gets sent to the MS unit so it knows what the AFR is.
Thanks for the info guys, I currently have an AEM wideband gauge so I'm guessing the signal wire from the sensor itself will have to be spliced into the megasquirt along with the gauge itself? What about the factory narrowband sensor?
 
If you are leaving the stock ecu in place you can leave the factory sensor in and hooked up. If you are removing the stock ecu then the stock O2 serves no purpose.

Out of the wide and controlled there should be a 0-5v output. That will be sent to the MS unit via the wideband input. Believe it’s pin #23.
 
Perfect, now that you say it I do remember a white output wire coming from the gauge that I didn't use. Well so far it all sounds pretty straight forward, I think my next steps are really just to order the unit and let them know what platform its for in case they need to do any internal mods like you said.
 
If you can solder and follow direction and have the time you could get the disassembled kit and put it together yourself. I built my MS3x like 9 years ago. It was time consuming but a fun process. The manuals are also a lot better setup now.

You can get a base tune fine from symtech labs repository. just don’t try to order from them. They went defunct years ago. I’m surprised the website is still up to be honest.

http://old.symtechlabs.com/support/msq_rep.php
 
I am currently installing a fully assembled surface mounted MS3 plus in a 420a car, fully replacing the stock ecu, we somehow have a blown daughter board which contains the processor within 5 minutes of trying to start the thing, likely either static damage to the board or factory defect, a few on their forums have had the same problem, there doesnt seem to be much support as far as caring that a $800 purchase is dead after 5 minutes of being installed, that leaves a terrible taste in my mouth, the support in general sucks for this thing if you ask me, I am used to installing the Link G4+ ecu's so I am spoiled on support and lifetime warranty. The daughter board itself is $230 so I am not too happy right now, as it looks like we are sol and I suppose just have to spend that much more to fix a new standalone. If I had known that my buddy was going stand alone I would have had him get the Link unit but he bought this without my knowledge.
 
How is this done exactly, any regulator in specific? Thanks Paul
I can't remember where the idea originally came from, but I think it was from Vortech or a similar company that sold a supercharger kit for the Neon. They suggested using a VR-125 voltage regulator from a late 1980's Dodge Omni. It turns out that works pretty well, so it has been the standard part for the job since then. Any online or brick-and-mortar parts store should have them. There's a connector available for it too.

Here are installation instructions: https://www.symtechlabs.com/docs/alt_voltage_regulator.pdf
 
The MS2 and 8’ harness will work. Just let them know what you will be using it on so they can do any internal mods when it’s being built.
Alright guys I have my pre-built megasquirt 2 v3.57 in hand from DIYAUTOTUNE. I have attached the quote sheet they gave me listing some of the internal mods that were done to the unit. They asked a bunch of questions before hand to come up with the right mods. I understand the 420a needs two ignition outputs, thus a spark output B being brought out to pin 10 on the DB15 plug. However, the 5V pull on tach input and jumper ECU for VR input I don't quite understand if someone can elaborate.

My plan is still to run this as a complete standalone unit in the car. I'm thinking I'll simply cut all the wires from the two plugs for the existing stock ecu and attach all the inputs and outputs from there into the ms harness. For the most part it seems pretty straight forward looking at the wiring diagram (see attached). My only questions are what needs to be done to run stock coolant fans, stock tachometer, speedometer. I know I can configure within tunerstudio to setup output wires but what wires would I be connecting exactly? I need a small fusebox? Can I use the stock relays for fuel pump etc.? I have the external voltage regulator for the alternator as well.

If one of you can just give me a brief rundown on how you wired in your ms for your 420a that would be great, either post it here or message me. Just trying to plan ahead and do as much research as possible before diving into this.

Thank you

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Alright guys I have my pre-built megasquirt 2 v3.57 in hand from DIYAUTOTUNE. I have attached the quote sheet they gave me listing some of the internal mods that were done to the unit. They asked a bunch of questions before hand to come up with the right mods. I understand the 420a needs two ignition outputs, thus a spark output B being brought out to pin 10 on the DB15 plug. However, the 5V pull on tach input and jumper ECU for VR input I don't quite understand if someone can elaborate.
The v3.0/v3.57 boards have two crank sensor input circuits: one originally designed for VR sensors and one designed for Hall effect or optical sensors. The VR circuit is a bit more versatile and works well enough for Hall effect (like in the 420A) and optical sensors with 0-5V+ outputs, so they configured your ECU to use that. The 420A crank sensor is a lot like a simple switch that makes and breaks a connection to ground. The output alternates between 0V (ground) and nothing (no connection). By adding a pull-up resistor, the sensor makes a 0-5V signal instead.

My only questions are what needs to be done to run stock coolant fans, stock tachometer, speedometer. I know I can configure within tunerstudio to setup output wires but what wires would I be connecting exactly? I need a small fusebox? Can I use the stock relays for fuel pump etc.? I have the external voltage regulator for the alternator as well.
You will need to build circuits for each of these things inside the ECU: something to trigger the fan relays and something to feed a signal to the tachometer. It's not just a matter of checking a box in the software; the ECU lacks the hardware to do these things by default. The stepper IAC outputs can trigger relays, but you'll need those for IAC control. The speedometer gets its signal directly from the sensor, so there's nothing to do there.
 
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