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Any questions you have before you begin buying, building and installing.
By Gossman
Hey everybody!

As most of the people I've read in this forum always say, I'm new to Speeduino and standalone fuel injection, but not new to the engine and engine management side of things generally. That being said, this will be my first foray into the field of building a standalone engine system for this and I figured what better way than by doing it on a $200 car! I've got myself an old EA81 (1982 Soob GL) and got myself an SPFI unit off of a 'newer EA82 unit. Cool stuff, but before I get much further on this build and please accept my apologies if it's redundant at this point, but I've read through pages and pages of this forum, the wiki, and facebook pages and I'm not sure if I've got this all right.

I'm going to be purchasing a Micro ECU from ... powerfull/ when they get back in stock (possibly NickZ here on the forums?) and had a couple questions regarding the installation and accepted inputs from the sensor I've currently got and how exactly they're supposed to wire up.

1) I've got a 4 wire TPS sensor that I believe I should be able to use 3 of the wires for my use but I could be wrong - can I omit the idle switch and use it as any other 3 wire TPS?:
TPS sensor.png
TPS sensor.png (37.43 KiB) Viewed 5616 times
2) My distributor is from the original SPFI system and has what looks like a 360 tooth encoder wheel read by an optical sensor of some sort. I've replaced the 360 tooth encoder wheel with a 24-1-1 optical wheel for a VG30E. A little modification and it seems to fit just right but I'm not sure where to go from there. Will this set up work okay without a physical crank trigger? And does a crank trigger even matter with an SPFI system?: ... DaVeTOMLx4
Optical Wheel.jpg
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CAS (Disty).png
CAS (Disty).png (25.89 KiB) Viewed 5616 times
3) Third concern is the coil. I also got it from the original SPFI system and it appears to be a dumb coil with some sort of ignitor attached on a bracket next to it. Will this work with the speeduino? If so, how would I go about wiring it up?
Coil 1.jpg
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Coil Specific.png
Coil Specific.png (33.9 KiB) Viewed 5616 times
4) Last major concern is the fuel injector itself. It's a throttle body injector of low impedance (2ohm) and high flow. I'm not sure what I could replace this injector with because it's so oddly specific, so my alternative was to buy a big resistor block and put it on the + of the injector, but I do not hold the hold open amperage so the resistor block will essentially be a "best guess" based on some arbitrary numbers I put in the injector resistance calculator... Do I literally wire this resistor physically 'in line' with the + connector and just have a giant ceramic block in my harness somewhere or am I an idiot?:
1F@20PSI = 133ml
800cc or 76pph

Really sorry for my noob questions but I've reached a couple places where none of the information I've found applies to me very well or it's way above my head... Thank you for all your guy's help ahead of time and I know there's more I'd like to ask but for now these are my biggest hurdles to cross.
By theonewithin
Your best bet is to read through the wiki as it answer the majority of your questions such as decoder wheel, ignition, TPS and injectors.
User avatar
Hi @Gossman - I see you've done some reading, so I'll throw out some stuff.
1) Yes, just use terminals B-C-D, but verify correct direction and true full range of signal.
2) If the wheel you're now using is the one I think it is, then you'd only use the 24-1-1 signal (no "cam" signal), set-up as 12-1 Missing Tooth at crank speed. Note Speeduino supports the Nissan 360 pattern, but I don't know the applicability to your original wheel.
3) My ref's say a PRW-1, but your photo does not match that, and looks more like a BM20x series. Not being sure, I would first bench-test that your diagram is correct (B+, Sig and GND through module mount). If not, post better images, info, or circuit diagrams.
4) The results of the Injector Resistor Calculator have worked pretty well so far. In your case, 2-ohms, 2A and 14V results in a 5-ohm 25W resistor. Mount it anywhere from the Speeduino output terminal to the injector terminal. On a heat-resistant surface is good. Update your progress!


Wire-wound resistors are the usual $2-3 go-to for injector resistors, and multiples can be neatly ganged. About 1"(25mm) long:
Wire-wound_5-25.jpg (17.86 KiB) Viewed 5579 times
By Gossman
1) Perfect! I can put an ohmmeter and run the throttle open and closed a few times to make sure it's within the proper range, right? Or can I calibrate it for this specific gauge if not?

2) Awesome! So I'll follow the set up in the wiki as a 12-1 crank sensor in TunerStudio, and then provide pin 1 with 12v switched, pin 2 and 3 to the ECU reference and position signal and ground it through the engine/chassis or an ECU ground?
P.S. The wheel i ended up going with I believe I linked in the original post. It looks a little less convoluted than the one that was already in the disty, but I've saved it incase the new wheel won't work. I was just pointed to this one by somebody on facebook and decided to give it a shot!

3) This is the only other schematic I have in the OEM service manual regarding the ignition coil circuit diagrams. I've also attached better pics of the coil itself. Hope this helps! I can get more!
SPFI Ignition.png
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Coil 2.jpg
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Coil 3.jpg
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Coil 4.jpg
Coil 4.jpg (229.69 KiB) Viewed 5526 times

4) Thanks for the clarification! I'll search online for something that looks similar to that resistor block as that's probably much better than what I was going to do. Would it be fine to mount that on the intake manifold near the throttle body or would it quickly overheat?

Again, thanks for all of your help! I'm trying my best to get as much of a plan set in stone for how I'm going to do things and sort out a roadmap before actually tearing the car apart because I would very much prefer the car not to be in the garage in pieces for weeks on end. I know I won't be able to plan it all out, but I need to start a wiring harness and relay block plan and build and I just end up stressing myself out if there are too many "I'll cross that bridge when I get to it" questions left on the table. Let's not even begin to ask about the idle up valve! : :lol:
By Gossman
I’m not trying to be confrontational here, and I respect your somewhat passive aggressive comment because you clearly know much more than I, and I hope to one day be where you are - but it may surprise you to learn that I have indeed been through the wiki several times. I’ve also lurked on here for quite a while. I’ve lurked on Facebook, google, MS forums, and asked a few questions here or there across a couple different platforms.

For instance - you say my TPS and crank set up are wrong - I do not understand how my understanding of the TPS differs in this instance specifically. On the wiki it says speeduino needs a variable resistance 3-wire TPS. - not a 2 wire on/off type. I appear to have both in one. As I’ve tried to make clear before; I do not understand EFI as you guys do. It says nothing about 4 wire switches and in the schematic for my switch that I’ve dug through many layers of OEM manuals for, it appears that this TPS has a power, ground, and a rheostat inside of it that I’m hoping will work as a 3 wire TPS. I just need to test it’s resistance, right? I have no other experience and it obviously does not mention my application anywhere that I’ve found so far. Quite understandably the wiki has nothing about wiring yet as that section is under construction, but I simply need help here. You say the answers are in the wiki, and if that’s the case, then it goes over my head and I simply don’t know what I don’t know then.

I’m sorry to clearly be putting you off with these evidently very stupid questions, but I do not know how to do this properly and I would really like to learn. Please believe me when I say that I have gone through the wiki. I’ve learned a lot and downloaded the speeduino manual, but the practical implications of certain things I just simply don’t understand.
Hey @gossman :)

Welcome to the forum.

I'm by no means an expert, and completely understand your difficulty applying the wiki to your project. Been there myself. :D

Something that may help, is for you to install Tunerstudio, and familiarise yourself with the different areas of the interface.

Regarding TPS. Once you have excluded the on/off terminal, determine the signal wire. The other 2 are + and -. It doesn't matter which way the + and - are connected, as the firmware will deal with it. You need to configure your sensors in TS (under tools). It will be as simple as putting you foot on the accelerator and clicking.

Regarding the large resistor for injection, I also have the location issue. I don't think over the engine is a good idea. Possible on a relay panel if you have one. Depends how hot it may get I suspect. Perhaps attached to the bulkhead.

One thing I have learned, doing is better than theory. :D
User avatar
1) Yes, but test the Signal pin to both (+) and (-) terminals for smooth and linear progression end-to-end. It may then be calibrated if the output voltage is within the 0-5V range.
2) Verify your sensor power voltages, as most are 5V, but in any case the signal output must be under 5V (or grounding with pullup) before it reaches the processor.
3) That coil driver appears to be 4-wire to me, with +12V and Signal on the spades, and wires to the coil. That assumes body grounding not shown. Find the power ground ;) Put it on the bench and test or scream at it until it either makes sense or you replace it with a known unit. There's too much involved for me to guide through "if-then" testing a BJT unit like this right now. Perhaps search for transistor testing methods. It's not hard, I just can't verify by looking at an image.
4) Yes, be aware they may get hot, and ensure the heat would not affect anything nearby.

By Gossman
Thanks for the clarification everyone! That helps me a ton and I will continue experimenting with my build to get something that'll eventually work. I did download TunerStudio a while ago and tried playing around with it, but I don't have a speeduino.ini file and I'm not exactly sure where to find one without having the ecu, or how to play around with the software without it. Can I play around with one of the other generic file types and then just transfer it over to the speeduino file or is there somewhere I can just get the ini file and play around with it?

I suppose I'll also need some sort of oscilloscope, right? TO properly test the signal references from my sensor to be sure the ECU can accept them?

As for the coil... Perhaps I'll just get a well known coil type and use that instead. Can't be that difficult to swap it out with a more modern unit, right?
User avatar
Gossman wrote:
Sun Jan 12, 2020 7:33 pm
… I did download TunerStudio a while ago and tried playing around with it, but I don't have a speeduino.ini file and I'm not exactly sure where to find one without having the ecu, or how to play around with the software without it.
Go here, download the full ZIP package of info and code: Or, download the latest version directly here:

With only an Arduino Mega or clone, you can load the code (using Arduino IDE or SpeedyLoader) and connect to TunerStudio. With a second Arduino (UNO, Nano, etc) loaded with Ardu-Stim (one example), you can simulate RPM, and some resistors or pots (or actual 5V sensors) will give you more simulated inputs to see in TS. Go from there.
Gossman wrote:
Sun Jan 12, 2020 7:33 pm
I suppose I'll also need some sort of oscilloscope, right? TO properly test the signal references from my sensor to be sure the ECU can accept them?

As for the coil... Perhaps I'll just get a well known coil type and use that instead. Can't be that difficult to swap it out with a more modern unit, right?
In each case, you have three choices — research what you have for info; test what you have for info; or use something else that has known info. Each has its up and down-sides for different components, so the choice is yours. Test equipment is always useful (including troubleshooting and diagnostics), but not always required, depending on which path you take. A multi-meter, logic analyzer and/or cheap O-scope (both from $20 and up) can certainly help at various points now or in the future. That's your call.

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