205 SI Megasquirt- Thoughts?

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Kendal

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Tadpole
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Hi all, I bought myself a little 205 SI a few months back for use as a daily driver but also as a relatively cheap and simple car to tinker with and hopefully learn a bit along the way. I'm fairly mechanically minded, but haven't done much more than oil and filter changes since high school- about 10 years. So it's been great to dive in and get my hands properly dirty once more- I've managed to sort out a few little quirks the car had when I bought it and now it seems to be running pretty sweetly.

But you know how it is, there's always the pull of the next project! I've been doing a bit of reading and thinking about what to do with it and I'm wondering about giving it the Megasquirt treatment, with the eventual goal of updating to a Gti manifold. I'm pretty confident with a soldering iron (I was using one before I got my pen license!), so the assembly doesn't really scare me. It seems like it'd be a relatively simple install too, as I believe the SI already has all the sensors required. It's the ignition that seems the most daunting. I've read most people recommend going the fuel only route first, then adding ignition later, but it seems like that'd be a major pain in the SI, having to run both ECUs together.

What are peoples thoughts? I couldn't find any reference to anyone doing the conversion on an SI, has it been done and would the gains be worth it?

Thanks
Kendal
 
Good idea. All you need is a GTi manifold/injectors/fuel rail etc. to make it worthwhile. Use the existing wasted spark ignition. Input can be standard 60-2 flywheel. Why can't it all be one module?
 
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PeterT said:
Good idea. All you need is a GTi manifold/injectors/fuel rail etc. to make it worthwhile. Use the existing wasted spark ignition. Input can be standard 60-2 flywheel. Why can't it all be one module?
Click to expand...

Thanks PeterT, I guess I wasn't very clear with the ignition. I've read a few people say that it's best to start with a fuel only setup and then add the ignition control later. It seems to me that that wouldn't really be the case for the SI, as a fuel only setup would mean retaining the old ECU to control ignition. So yep, I'd be looking at doing it all from the one box, but from the digging I've been doing in the megasquirt manuals it's the ignition setup that seems most daunting to me.
 
No real issue, get some LS1 or LS2 could, directly controllable out of the box. Any Commodore wrecker will suite. Allows you to tidy up a bit too.
 
you shouldn't need ls1 or ls2 coils. As mentioned just use the existing si coilpack. but you may need to add an aftermarket ign module. get the good megasquirt kit that does fuel and ign. it all open source so info will be out there somewhere. Wait for Graham to chip in as he has first hand experience with megasquirt and 205s
 
The coils will certainly need a module to carry the current, unlike an LS1 coil which has a built in ignitor. The Si coil pack is so neat and tidy. It would be crazy not to use it. You can buy dual channel ignitors quite cheaply.
 
Kendal said:
It's the ignition that seems the most daunting. I've read most people recommend going the fuel only route first, then adding ignition later, but it seems like that'd be a major pain in the SI, having to run both ECUs together.

What are peoples thoughts? I couldn't find any reference to anyone doing the conversion on an SI, has it been done and would the gains be worth it?
Click to expand...

I recommend against starting with fuel-only in your case. Ignition is not hard at all as long as you know your advance curves. Going fuel only you'd have to share sensors (or double up) with the ignition ECU and that, as you say, could be a major pain. If you don't know your advance curves it shouldn't be too hard to read them from your standard engine with an advance tester type timing light. And there's always the possibility of a dyno tune afterwards to optimise your timing.

Pretty sure you'd need to use the MS2/Extra firmware to support wasted spark and a 60-2 toothed wheel. An extra BIP373 chip added to the standard MS2 kit should see you right for igniter duties.

Have fun,

Rob.
 
I'm thinking of using my spare MS1 to do this, using the original ignition as you suggest.
I would have thought the ignition side of things would just use revs and manifold pressure so the TPS could be liberated for the MS also the temp sensors. You would then need to trigger the MS, could be done by using a pair of diodes feeding from the inputs to the coil pack perhaps? There are many MS input options for triggering available.
Aftermarket management should make a big difference to this engine, it seems to rely heavily on feedback from the oxy sensor and there is quite a lag after putting your foot down, a new oxy sensor usually improves things a lot.

Standard MS2 firmware will support 60-2.
 
I'd buy a 2nd hand Haltech for $300 before I had car with two ECU's. So Heath Robinson.
 
Although you will need to leave the original ECU in place as a lot of the wiring in the car uses this as a junction point.
To do it properly you would need to redo the wiring from scratch.


PeterT said:
I'd buy a 2nd hand Haltech for $300 before I had car with two ECU's. So Heath Robinson.
Click to expand...
 
GRAHAM WALLIS said:
Although you will need to leave the original ECU in place as a lot of the wiring in the car uses this as a junction point.
To do it properly you would need to redo the wiring from scratch.
Click to expand...


So Graham, is that to say that using a MSII extra for fuel + ignition I'd have to redo the wiring rather than using the original loom with an adapter? What other systems run through the ECU in the SI? If it was a project car, that'd be a good excuse to reduce the rats nest of wiring in the engine bay, but as a daily it could be a problem. Definitely too much for one weekend!

I had a new O2 sensor on order, but apparently Bosch can't supply one until late August at the earliest, so I guess I'm going to have to look other places. Any recommendations?
 
Just go to Bursons or similar and buy a 4 wire sensor for $50, you will just need to cut and join wires.
I forget which wires go to the ECU but I know we got into a bit of trouble when we removed it in a mates car.
Maybe if you were to use the original loom as you suggest you may get away with it but it would be a real headache sorting everything out. I use a megasquirt loom when I do conversions, means you get a properly terminated DB37 connector as well. It is hard to solder car loom style wire to these connectors.

Kendal said:
So Graham, is that to say that using a MSII extra for fuel + ignition I'd have to redo the wiring rather than using the original loom with an adapter? What other systems run through the ECU in the SI? If it was a project car, that'd be a good excuse to reduce the rats nest of wiring in the engine bay, but as a daily it could be a problem. Definitely too much for one weekend!

I had a new O2 sensor on order, but apparently Bosch can't supply one until late August at the earliest, so I guess I'm going to have to look other places. Any recommendations?
Click to expand...
 
the si has the two brown multi plugs like the gti but ive never looked at the ecu side of things too hard. Graham is the si ecu mounted in the same place as the gti? I can only assume if it doesn't come out like a gti ecu and loom then is it wired back into the the fuse box near the glovebox area of the car? or the muti plugs are different?
 
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