Microsquirt Newb

Another newb thread....

I'm working on sourcing parts and reviewing wiring diagrams to convert my 83 244 Turbo from k-jet to Microsquirt. Going wasted spark using LS truck coils and the Yoshifab DSM CAS adapter. At the same time I'm adding an IC, replacing the exhaust (turbo back), and adding a 940/960 electric fan.

Everything looks pretty straight forward as far as hardware/sensors/injectors/etc needed and wiring under hood. There are a few finer points that I'm getting some conflicting information online or just not understanding the best way to go about something. Some of these things may be crystal clear when I actually start diving into this hands on, but I'm trying to plan this out as much as possible to alleviate any unnecessary downtime and doing a half assed job.

1. Power to the MS unit itself. Are you using the 12v constant and keyed on from the stock fuel pump relay location to power everything your MS install (relays for the MS, FP, coils, injectors, etc)? Or are you pulling from a separate source?

2. Confused a bit about Microsquirt with wasted spark. Originally I was looking at a MS guide that made reference to jumpers on the board itself to get this done. As I dug deeper I found the PDF install guide I'm looking at now (appears this is the most recent version). It makes no reference to any physical modifications to the unit itself...merely wiring options/requirements for pairing desired coils and of course changes in the settings in the software? Is it correct that the Microsquirt unit does not require any physical modifications to the board?

3. Original plan for the 940/960 fan was using a Saab or equivalent aftermarket sensor housing with a BMW dual temp sensor to control. I'm conflicted as to whether or not to have MS control the fan or to keep it separate. I like the idea of complete separation from the engine management, but on paper it seems using MS makes for a less complicated overall install since I'm building a harness anyways. Any advantages or disadvantages to going either way with this?

4. Can you share photos of your wiring solutions for the fuses/relays for the MS, and mounting solutions? Looking for some Volvo specific inspiration and ideas to keep things clean/organized.

If I recall correctly from my research on the microsquirt, running waste spark with LS coils on a 4 cylinder would take up all the available aux I/O, there's only 2 on a micro.

That is what I thought at first as well, however in the manual its showing for COP you would use IngOut1, IngOut2, WLED, and ALED. One per output. What is throwing me off a bit is scrolling down further into the wasted spark section its showing an example of an 8-cylinder running 8 LS coils, pairs of coils paired to the four above outputs. Since I'm going WS...based on this and what I've been reading online I should be able to pair to my IgnOut1 and 2, leaving my WLED and ALED outputs open.

Unless I'm completely off. Feel like I'm losing my mind a bit going down this Google search MS rabbithole.

yes you would just use ign1 and ign2 for wasted spark.

When I converted my '85 K-Jet, I decided to use a LH2.4 harness so that I could break in the new motor using LH2.4, then adapt to MS later (using a plug&play type setup). It also lets me go back to LH if I get tired of fussing with MS.

For wasted spark using COPs, you want to set MS to "wasted spark", using 2 outputs. MS also has a "wasted COP" setting that uses 4 outputs, but triggers them in pairs -- you'd only use this temporarily if the cam timing isn't working (and assumes that you want full non-wasted cop eventually).

If you have the spare output pins, running a couple fan relays off MS is nice -- very easy to set and change the on/off temperatures.

#1 Follow the recommended wiring diagram in the manual

#2 There is only one manual you should be reading and it is found @ msextra.com/manuals/ms2manuals/
In section 2 "Hardware" scroll down to MICROSQUIRT. Download the PDF then print out only the pages that apply to your install.
The setup manual is a big help when you are done wiring.
The CAS is a hall type sensor so you do not need any jumpering inside the case.
There are 2 ways to do "wasted spark" with COP, use the wasted spark setting and pair up the coils, or use "wasted COP" and use all 4 outputs.
You can do sequential spark with the CAS depending on which trigger wheel is installed. DIY Auto trigger-wheels/
The 24-1-1 setup works sweet setup as a 12 tooth crank speed wheel for a fast sync

#3 I'd use the MS to run the fans if you have the outputs to spare

#4 No way I'm showing anyone my wiring hacks

Test everything before wrapping up your harness, don't ask why or let your ego say it's all good. Nothing worse than to have to rip up all your work to make one small change.

#1 I have the main side of the fuel relay, triggered by the key, powering mine.

#3 Do it on MS just so you can fine tune it from the seat.

#4 I think the trick to a good MS install is to use mostly black wires of varying gauge and then shove the whole deal behind the glovebox wherever it fits.

Thanks for all the info guys.

Cwazywazy said:

#4 I think the trick to a good MS install is to use mostly black wires of varying gauge and then shove the whole deal behind the glovebox wherever it fits.

Click to expand...

Would probably want to use different color wire nuts to keep track of which splice goes where. I have a huge bag of them from HD.

Hoping to clarify a few things as I read through the manual again and order the necessary parts to make this happen. Between the manual, you guys, and a ton of online searching a lot of things are pretty clear but there are still some items that just aren't clicking. Much of this may be the info overload stage at this point...please be gentle.

Setup again is microsquirt with wasted spark LS truck coils, DSM CAS with Yoshifab trigger wheel. I'll be pairing the coils using Ign1 and Ign2, leaving the other two optional outputs open. This is a kjet car so will not be using any existing harness.

Based on the manual it looks like I only need to utilize VR1- for the CAS since I'm not Wasted COP. But, I'm seeing quite a bit of conflicting info here on the board in my searches. For my setup I do not need to wire in VR2-, correct? Is there any reason I should just wire in the VR2- when it comes to any diag procedures I may need down the road? I have no plans on going Wasted COP, but obviously wiring it in is not a big deal at this point.

Scratching my head a bit with the TPS VREF. Based on all the appropriate diagrams the TPS VREF out is going to split off to multiple locations: TPS, MAP, VR1-, and VR2- (if needed). Originally I thought I needed a 1k pull up to my coil pairs but it looks like that is only needed on the two optional ALED or WLED outputs for a Wasted COP setup, which I won't be using.

My confusion at this point is with this is the jump from TPS VREF with a 1k pull up to the VR1- (and VR2- if needed) wire between the CAS and ECU. Is it as simple as it looks in the diagram...jump from TPS VREF with a 1k resistor to my VR1- lead from the CAS back to the ECU? Where in the loom is the best place to make this happen? Seeing these are twisted and shielded in the MS harness, it seems it would be best to jump in at the connector to the DSM CAS itself or back in the passenger compartment closer to the ECU?

I'm also curious as to why this jump is needed. Not to question the people putting this manual together, but to learn why it is a requirement to jump a 5v output from the ECU with a 1k resistor to a sensor input back to the ECU. Really trying to get a better understanding as to why for my application.


Lastly...grounds. MS manual is very clear on grounding sensors and the unit itself. Quite a few guys with our particular applications are grounding sensors at the engine and the ECU back where the stock ECU grounded. I'm all about following MS's instructions on grounding and have no problem doing so, but curious if you guys have any different experiences or suggestions with grounding.

you need to wire up both the cam and crank sync with the CAS if you're running wasted spark, or have a missing tooth crank speed wheel (which the yoshifab trigger disc is not, and neither is the DSM disc iirc). So you'll be using both vr1 and vr2.


a pull up resistor is exactly that simple... a resistor between a +V and the signal wire (be it 3v, 5v, 12v, whatever). It's used to bump up low level logic outputs. If you're really curious, google it and read up, it's not limited to just megasquirt stuff.

grounds are best run to the battery negative for noise reasons. you can tie in to other ground locations, but run the risk of inducing noise. You may or may not run into issues if you use other ground locations depending on various factors. You also need to verify the +12v reading on ms matches the +12v at the injector clip or you will likely get strange injector behavior.

Another CAS option is to use a DIY trigger wheel 24-1-1.
That can be used as a crank speed 12 tooth -1 for a fast sync.
Only that one input is needed for wasted sparks (as it is a missing tooth wheel).
The second input, a cam position to establish 720? cycle phasing is needed for full sequential operation (or to establish crank position on a non-missing tooth wheel).


Some logic level devices have a vague or floating state that is not definite.
A pull up voltage applied to the device output creates a definite square wave signal. (on or off)

If you're going wasted spark, why not skip the CAS and use the stock 60-2 flywheel pattern and stock VR sensor?
This is by far the easiest system to wire in, in my opinion.

Thanks again for all the info, guys. Things "got real" as soon as I submitted the order and despite at least a month of reading through various sources I start second guessing everything. This combined with my last failed project (long completely different automotive project story) and a tendency to over think things is really getting to me mentally. So I truly appreciate this info.

culberro said:

If you're going wasted spark, why not skip the CAS and use the stock 60-2 flywheel pattern and stock VR sensor?
This is by far the easiest system to wire in, in my opinion.

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Honestly it was an option that never hit my radar. My search started with the kjet to MS guide here using the CAS so that occupied most of my research going forward. For a moment I did consider dizzy with an MSD box or equivalent, but I had some issues with a bad 6al back in the day that left a bad taste in my mouth. I also felt the CAS was a much cleaner/simplified install in the engine bay in comparison.

I’m a fan of it. It’s a lot cleaner than a stock dizzy setup, and the CAS as well. You just remove the stock distributor and use a 40mm plug to seal up the hole.
Another benefit, is that you don’t have to deal with clocking the CAS unit or a distributor ever again. Slap the flywheel on with the missing teeth on the stock location, and set crank offset to about 84deg (I think). That’s it

Yeah hindsight it would have been a great option. Bummer it wasn't something I caught prioras it would have been very tempting to T5 swap at the same time as well. I'm already committed to the CAS route though.

Alan29 said:

Yeah hindsight it would have been a great option. Bummer it wasn't something I caught prioras it would have been very tempting to T5 swap at the same time as well. I'm already committed to the CAS route though.

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it's alright, people fight with the vr sensor for the 60-2 almost incessantly, almost no one has issues getting the CAS to work. (fwiw I don't know 100% why folks have such a hard time with the 60-2 stuff, but VR signals in general can be difficult to get working cleanly)

I'm running d514a ls7 coils in wasted pairs, triggered by a 60-2 flywheel pattern. Like everyone else who has ever done it, I had to add a resistor across the + and - of the stock VR sensor to eliminate a breakup over 4k rpm. Have not had any issues since... zero, it works extremely reliably.

linuxman51 said:

grounds are best run to the battery negative for noise reasons. you can tie in to other ground locations, but run the risk of inducing noise. You may or may not run into issues if you use other ground locations depending on various factors. You also need to verify the +12v reading on ms matches the +12v at the injector clip or you will likely get strange injector behavior.

Click to expand...

Ok cool its starting to make a bit more sense but could use a little more clarification on the grounding scenario. So instead of grounding the MS unit to the head/engine, it is advised to run its two power grounds directly to the battery. My sensor grounds (CAS, TPS, MAP, WB sensor ground, etc) still go to the MS sensor ground lead as normal.

Regarding other grounds tied into other locations...is this where I would look to take my power grounds from the coils, injectors, and WB directly to the battery as opposed to the engine?

Are there any further precautions I should for shielding any wiring beyond the already shielded VR leads from the CAS?

Again I'm sorry if these are stupid questions, but noise hasn't been a concern on the types of basic wiring I've done in this past where grounding location isn't much of an issue.

you can ground the coils to the engine. ground (and preferably power) the wideband from the same source as the MS to cut down voltage differentials causing a skew in the readings. Injectors don't have a ground as such (the ecu does that).

Occasionally folks have introduced noise on signal wires coming in to the ms with proximity to outputs (esp high voltage outputs like coils), so I'd suggest you try and separate the outputs from the inputs as best possible in the loom.

I haven't looked at the MS grounding schemes in ages so I've forgotten the details. In general, the best configuration for all the low power sensors is to ground them to MS "sensor ground". Some of the K-Jet/LH temperature sensors ground through the block, but I think the LH2.2 temperature sensor has 2 pins and does not ground through the block (the LH2.4 sensor has 2 pins but is dual sensor with grounding through the block).

What Wideband O2 sensor are you using? Does it provide separate sensor and power (heater) ground wires? If not, you probably [?] want to wire WB02 ground to a MicroSquirt power ground at the MicroSquirt.

I'm not sure what's the best setup for +12v injector power and +12v MS power. I'd think that connecting these together near the injectors would be best?

The CAS uses hall sensor outputs, not VR, and thus has better noise immunity.

Going back to adding a factory 60-2 flywheel/flexplate vs. CAS, the issue you'll run into with a B21 block is the mounting of the CPS bracket. The B230 blocks have 2 drilled and tapped bump-outs in the bellhousing for the CPS bracket. The early B21 blocks do not have the bump-outs, but my 84.5 GLT B21FT block did have un-drilled bump-outs. Without the bump-outs, you'll need to make a custom CPS bracket -- it took me way too may hours to do this for a rebuilt '82 block (drill press, hacksaw, and metal file).