Motronic for ignition only inquiry

[LJ851]

I have a an '82 SC that i am putting an '86 3.2 engine into. I am going with PMO carbs for various reasons including sound and visual appeal. I understand most the functions of the various sensors and switches Motronic uses but am not sure how many of these parts i need to use the ignition only. My engine is missing the speed and reference sensors and CHT sensor and i don't want to buy any sensors i dont need.

My goal is to have a minimal as possible wiring harness (removing all the fuel related portions and unused sensors) for aesthetic reasons , has anyone done this? Obviously the AFM will be out of the loop, how do i end up with the most effective timing curve? Yes, i already searched.

[Quicksilver]

Well straight off you have to have the reference senders because they control the timing. You probably need most of the other sensors too as it needs to know the environment before it can see what map/settings it should be working from. If I was set in going this direction I would give Loren at System Consultants a call as he has real back-of-the-hand knowledge of how all the systems work together in real life.

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That being said I wouldn't ever consider going this direction. This is like selecting a 20# sledge to open your christmas gifts... Yeah they will be open but there are better ways.

If you really want an electronic ignition module I would look at megasquirt or the Ford modules that are popular with hobbyists. They are less expensive, have flexibility of parts, and they have a great level of do-it-yourself support. You will need to create your own advance curve so the ability to program it yourself is important.
I'm trying to think of a reason to go to all this trouble if you are running carbs though. The advantage of electronics is mostly in fuel control. If you aren't doing that then I can't see a reason not to run a distributor and use an electronic points replacement of some sort. A lot simpler, a lot easier to support, and a lot less expensive.

[LJ851]

I agree the Motronic to run ignition only is not using all it's potential but so is using any standalone ecu as well. Motronic is also very durable, well proven and does a great job. Let's see how a megasquirt is doing in 25 years.

I also have most of the Motronic system already.

The 2.7 dist appears to be the only bolt in unit to fit the 3.2 and needs to be recurved i am told. That is enough money to push me towards my other option of the electromotive crankfire set up.

As far as my choice of carbs, it is purely a heart decision not a logical one. I have owned and tuned a few cars with standalone ecu's and dyno tuned countless carbed and fuel injected motorcycles so i am familiar with both sides. (I just converted my ducati to fuel injection last year) Plus, the PMO carbs seem to hold their value really well if i ever did want to put throttle bodies on later.

[Chuck.H]

Hmmm, let's think about this.

The timing is mostly controlled by three main tables, and then adjusted with a few others.

The main tables are idle, WOT, and part-load.

Idle and WOT are used when the throttle switches are closed - you'll want to add these to your PMO linkage. Part-load is not so simple, as this is a two dimensional table based on RPM (which you can get by installing your speed/ref sensors) and load, which comes from the (now missing) barn-door air sensor.

I think it will work if you replace the barn-door with a MAP sensor in the manifold (search for 'pressure sensing motronics' as people have done this before).

This leaves CHT, which motronic does use to compensate timing based on a cold or hot engine, so add that back also. So, IMHO you need to use every sensor in one form or another, sorry.

BTW, if you don't use the MAP sensor, I think you can still get it to work, but your part-load table will be effictively one-dimensional, still not bad considering the control you will have (can you burn EEPROMs?)

Hope this helps,
Chuck.H
'89 TurboLookTarga, 332K miles (with MAF sensor in place of barn-door)

[Tippy]

If you are running carbs, why not just run the SC dizzy/ignition and call it a day?

That hands down would be easiest.

[Tippy]

Originally Posted by LJ851

Let's see how a megasquirt is doing in 25 years.

Ok, I'll bite. Where are you going to get replacement parts/chips for the Motronic when they fail?

There is only so many workable units left in the world.

The MegaSquirt bits are very common components, not special one-off Bosch stuff.

[LJ851]

Originally Posted by Tippy

If you are running carbs, why not just run the SC dizzy/ignition and call it a day?

That hands down would be easiest.

I wish it was that easy! I even have one of those. Th 3.2 dist spins backwards compared to all the 911 dist's except the 2.7 so my SC unit would be mechanically retarding.

[gtc]

Single plug electromotive systems pop up in the used parts classifieds fairly often for under $1000. Seems like that would be one of the easier ways to get it done.

[Tippy]

Quote de Tippy

If you are running carbs, why not just run the SC dizzy/ignition and call it a day?



That hands down would be easiest.

I wish it was that easy! I even have one of those. Th 3.2 dist spins backwards compared to all the 911 dist's except the 2.7 so my SC unit would be mechanically retarding.

So you can locate the 2.7 dizzy and then call it a day?

Not sure if the rest of the SC ignition bits adapt to the 2.7 but if it does, sounds pretty easy and far easier than the Motronic stuff.

Just a thought and at least get you up and running quick.

[LJ851]

Does anyone have any first hand experience with my original inquiry?

[Steve@Rennsport]

Originally Posted by LJ851

I have a an '82 SC that i am putting an '86 3.2 engine into. I am going with PMO carbs for various reasons including sound and visual appeal. I understand most the functions of the various sensors and switches Motronic uses but am not sure how many of these parts i need to use the ignition only. My engine is missing the speed and reference sensors and CHT sensor and i don't want to buy any sensors i dont need.

My goal is to have a minimal as possible wiring harness (removing all the fuel related portions and unused sensors) for aesthetic reasons , has anyone done this? Obviously the AFM will be out of the loop, how do i end up with the most effective timing curve? Yes, i already searched.

The Motronic system needs crank position & reference sensors to handling timing and sense RPM. You'll not get access to all the timing maps since the PMO's will not offer load and throttle position information.

Its really FAR from ideal and you will leave plenty of throttle response and power on the table. BTDT, and its not great.

My best suggestion would be to use a CCW distributor (recurved OEM Bosch or JB Racing) and an MSD ignition to get the best performance and fuel economy out of this package. I've done both and properly done, works VERY nicely.

[ischmitz]

If you want to be adventurous maybe look into Megasquirt-II. While it was developed for fuel delivery initially MS-II and later versions control ignition as well.

Other than Motronic you can program ignition maps freely and use MAP to get a 3D map (RPM, MAP). You do need a crank position sensor though.

[strictly]

LJ851

apologies to drag up a TFTD but im wondering how you got on with this?

Im in a very similar position to you (i.e a 3.2 (taken to 3.4) with no sensors/fuel injection (bare block) but this time for a 3.2 (came with no engine, but half the wiring loom is missing to =((

so im currently looking at my options. I happen to have some PMO 46's to hand so your original post mirrors mine...

Im half deciding between selling the pmo's and finding a complete motronic injection system, vs fitting the pmo's and figuring out how to do the ignition side, im searching old threads and using that to guide me.

im going to look at what cams, etc are currently fitted but thats a different story!

[LJ851]

I ended up making my carrera distributor a functional unit (basically a clockwise spinning SC distributor) by using a variety of bosch distributor parts. I am triggering a MSD 6al and it's been faultless.

[Jonny H]

Lock the dizzy and use one of our fully programmable CDI+ boxes? You could retain the SC harness and it'd all look stock.

[Omegaman]

^what he said :-)

[strictly]

Originally Posted by LJ851

I ended up making my carrera distributor a functional unit (basically a clockwise spinning SC distributor) by using a variety of bosch distributor parts. I am triggering a MSD 6al and it's been faultless.

ah intresting, probally going to be my best attack point to, there is so much of my motronic missing im best forgetting it was every there!

So basically you took your 3.2 dizzy and built it work like a normal distributor where you can change the timing. How did you work out what parts to use/distributor curve or was it just pot luck? I get that i then need MSD (but i could also cdi/perma tune i presume).

Do you think my best starting place will be a 2.7 or 2.4 dizzy? Is yours full mechanical advance or has a vac advance as well (i havent checked my pmo's yet (for the vac connection - if mine have one)

[strictly]

Originally Posted by Jonny H

Lock the dizzy and use one of our fully programmable CDI+ boxes? You could retain the SC harness and it'd all look stock.

Hi johnny, ah ha intresting. The advance curve is fully programable with your cdi? Do i still use a dizzy or use a crank trigger wheel (thats actually wants currently fitted)

I read your article in one of the mag's a few months ago, ive still got it, i'll have a reread of it

I love your light mettalic green sc that you had in the back ground. I had the exact same colour in a 78sc (LMG with cork interior). Man i miss that car, that was a nice sc!

Im in the UK too.

Luke

P.S. Edit - johnny ive had a glance at your website ok cool, i see the advanced cdi unit can do quite a bit, and answers my questions!! I'll going to re-read your article, and put it on the options list

P.P.S if you ever decide to sell your sc, give me a buzz, ive got a couple of 911's im sure we could discuss when the time comes (i.e if you fancy a change)