Locked distributor with MoTeC

[Number 7]

Following on from my earlier post about removing ARP head studs, the engine is now undergoing a full rebuild at TVR Power.

Now I have what may well be a dumb question, but as I'm no mechanic, I need to ask it: my setup is a very early MoTeC ecu controlling ignition as well as fuelling. The distributor is retained, but locked up somehow, and used as a cam sensor I think, with the ignition settings being in the ecu map. Unfortunately the dizzy was removed before the builder was aware of this setup. My concern is knowing how the dizzy will be refitted in exactly the same position as before. If it isn't, wont the ecu be firing at the wrong time?

[sidecar]

Marking the dizzy and then putting is back in the same place is a good starting point only, you should always then time up the ignition system with a strobe. I can take out my dizzy and the refit it and get within 2 degrees but that is about as good as you can ever get with this method.

I run a locked out dizzy with a programable MSD system, I've no idea how your system works but I think that you will need to find out. My system 'adds' retard, the dizzy is actually timed up at 46 degrees BTDC, the MSD then 'pulls' out the timing according to a curve that I programmed into it via the software that the system came with. When it is pulling out zero degrees I'm running 46 degrees of advance. (Over 3000 RPM and with a high manifold vacuum).

[Number 7]

Thanks Sidecar. That's what I feared. Engine builder is not familiar with the system and the company that fitted it years ago has long since gone. I even had to send it to Australia a couple of years back for a checkover, as no one from MoTeC in the UK could do it. Finding a MoTeC dealer in the UK familiar with the RV8 I imagine would be impossible. I'd rather not wreck my brand new engine with wrong ignition settings. I might fire off some emails to Australia.

[DaveEFI]

When you say it's used as a cam sensor, that normally means there is a crank sensor too. And that's the one which gives the accurate ignition timing.
The cam one then merely the engine phase. If it is the latter, the timing of that isn't usually critical. But if the locked dizzy is providing the primary tach signal, obviously needs to be set as before.

But the only real way to know would be to check the manual for your particular injection.

[garrycol]

I had a 123 electronic ignition setup on another make of engine. Same basic logic will apply.

Now the distributor you have will be being used as a crankshaft position indicator - as it is in a simple points dizzy system. Yes is it being driven by the camshaft but it is telling the ECU where the crank shaft is. Of course the timing chain has to be set up correctly for it to do this.

I am surmising now but I bet I am right. On my 123 system I just set the engine to TDC on the power stroke and I rotated the dizzy until a little light comes on - but with is just a cheat so you don't have to pull it apart - the light comes on when the rotating sensor inside the dizzy lines up with No 1 cylinder when the engine is at TDC on the power stroke - really no different in doing an initial setup for an oridinary dizzy.

So set your engine up on TDC on the power stroke (so it is not 180 degrees out) and put the dizzy so that the sensor is pointing to No 1 cylinder. When the dizzy is in its rough position then turn slowly until the pointer/sensot is accurately pointing to No 1.

Of course you could always read or download the setup instructions for your system

Garry

[stevieturbo]

When you say it's used as a cam sensor, that normally means there is a crank sensor too. And that's the one which gives the accurate ignition timing.
The cam one then merely the engine phase. If it is the latter, the timing of that isn't usually critical. But if the locked dizzy is providing the primary tach signal, obviously needs to be set as before.

But the only real way to know would be to check the manual for your particular injection.

Pretty much this.

BUT...it really depends what the crank trigger is. If there is no TDC reference then cam trigger position is absolutely critical, if there is a TDC reference on the crank, then it can be less critical.

But ultimately your ecu will have been told where to look for the cam trigger and of course it will want it to be there. So it needs to be re-installed where it was before.
If different, you'll need to check within the ecu to see where it was, or where it can be and tell it the new position.

So really you'll need to be looking into the software to find this out, I doubt a manual will ever tell you unless it's a system that insists on the cam trigger location being in a very narrow range.

However...what ecu is it, and just how old is it ?

The fact you're retaining dizzy for sparks, means as far as they go...cam trigger location can be less important, simply because the mechanical dizzy/single coil controls where each spark goes to.

So for this setup a cam trigger isnt really important at all.

You really need to find out what way the ecu really has been configured.

[DaveEFI]

Reading again, I'd guess it's the dizzy which is providing the primary tach signal. And likely the only one. Can't really see a system having fully sequential injection but dizzy ignition.

Again just speculation, but most mappable ignition systems allow an offset to be entered to trim the static timing. You should be able to find that in the software. So setting the dizzy by eye should be close enough to get it running, then check the timing against the software settings using a timing light.

[stevieturbo]

I'd agree, but sequential is the main season for a phase trigger.

If it was all done correctly, then simply pointing rotor arm to no1 as usual, with dizzy installed as per original should be ok to get it started

Is there a crank trigger ? Sounds like maybe not

[DaveEFI]

Yes. But if it is an old after-market programmable ECU, would it even offer fully sequential injection?

I suppose you could modify a dizzy to give the primary tach signal and the phase one, but I've never heard of anyone doing it.

[stevieturbo]

Sequential is nothing new, I've used 20 year old systems that offer it

Point is with his, it probably isn't sequential anyway, and the dizzy is the only trigger, and more than a single tooth, although a single tooth on a dizzy could do it all, albeit crudely

We need more info

[Number 7]

Thanks for all of the contributions chaps. There is no separate crank trigger. The injection is not sequential either - this is a very early MoTeC ecu. I had it fitted in '99, and it had probably been on the shelf for a number of years prior to that, but despite it's age, and the compromise of retaining the dizzy, it works very well. Doesn't have all of the bells and whistles of modern stuff, but it suits me fine. I think I may have a manual somewhere, so I'll dig it out, although whether it's going to mean much to me is another question. The answer I got from MoTeC support is I think essentially what has been suggested here: put a timing light on cylinder 1, and move the distributor to match the reading in the map. Will find out in a week or so.

[stevieturbo]

If you do the usual point rotor arm at cylinder 1 when it is at tdc firing stroke, that will at least get it running, or very close to it, then check from there