Digiplex ECU

[Piero]

Hi,
I need to use the distributor of a Strada 130TC Abarth on my RWD 131 engine. I will be mounting it on the exhaust side cam box.

I have distr + sensors, crank pulley, but no Digiplex ECU. I have the distr base mounting of a Beta Volumex to mount it to the ex cam box, for the correct oil drainage.

What I am hoping to learn is, how good is this set up, is there a better more modern ECU that I can buy? If I am stuck with the original Strada 130TC ECU, how will it cope with a tuned motor?

Many thanks
Piero

[SteveNZ]

Microplex ignition is very good for its time. Fully mapped so such better than any centripetal distributer. It cannot be altered for a modified engine though. Not without some creative mods anyway.

[Piero]

Thanks Steve.

Not quite sure about what "it cannot be altered for a modified engine though".. Are you talking about the Strada ECU or a centrifugal distributor?
Can a dyno man remap a modern ECU to work for my tuned motor?
What would be a good make or model to use?
Will it have, and do I still need the vacuum hose?

Many Thanks

Piero

[NickRP]

Piero,

If I were you, I'd stick to Digiplex, at least for start. It is not programmable, that's true. But still, it is programmed in the way which works fine for many many DOHC applications.

All the best,
Nikola

[Guy Croft]

Nick, hi

The Digiplex reads rpm, crank tdc and manifold vacuum only from one port.

It has 512 stored ignition values and determines the best (?) according to those the input parameters of manifold vacuum and rpm.

I imagine that if the vacuum condition at a given speed does not mimic the original engine the advance it selects could be way off optimum for that engine.

The reason I ask is that I have heard no-end of reports of low speed misfire/hesitation on 130TCs with Digiplex on non-standard engines and wonder if this may a contributory cause. Perhaps not.

The Microplex - by the way - is only for the Delta Turbo (carb) system - mentioned in an earlier comment.

GC

[NickRP]

Hi Guy!

You said - Digiplex is reading signal only from one port. This shouldn't be the case, it should read vacuum (i.e. its mean value) from all the ports, joined together by vacuum rail. Otherwise, individual port pulsations will surely "confuse" it.

As vacuum is used for load sensing, sure, with modified engine this will be misleading to certain extent (the more agressive the cams, the more prononced the problem).

I do not have hands-on expirience with 130TC. However, I took part in a few low budget racing SOHC projects, where keeping the original electronics (Digiplex 2) was prerequisite. There were no troubles with it, I admit. When the vacuum signal was too weak (causing odd ignition advance fluctuations at low revs), people often remove the vacuum tube. Not the type of the solution I particulary like, but still, it worked (suprisingly) well. Static advance can be adjusted, of course, by moving the sensor relative to the crank.

Did you get reports of Digiplex problems also on other Digiplex equipped cars (especially Digiplex 2)? Maybe 130TC Digiplex has some bugs in it... who knows.

Regards,
Nikola Radenkovic

[Guy Croft]

It definitely only reads vacuum from one port, Nick, no.4, see GC book p140 if you've got it, there is a factory schematic there.

Now, I don't have the faintest idea how vacuum condition varies in absolute terms from one engine to another or what the benchmark vacuum/load characteristic is even for the 130TC in standard trim. It's going to be risky to use a premapped system on a non-original layout. If it runs well, that's great. If not, you may not ever know why. I am at a loss to suggest any other alteration to the Digiplex setup other than 'don't use it' - because it might prove less effective than a conventional distributor. You certainly cannot reprogramme it, not as far as I know anyhow.

There have been 2 or 3 threads on the site regarding Digiplex equipped 130TCs hesitating or misfiring on pickup. See for example:

http://guy-croft.com/viewtopic.php?p=2578#2578

I'm wondering - and I hate to say this, whether an improved layout might be linking the ports together for the vacuum signal. Anyone care to try?

Piero - I think my advice is not to use Digiplex or anything associated with it. If you want programmable ignition get Weber Alpha from Northampton Motorsport 01604 766624, friends of mine and members here.

GC

[SteveNZ]

The Microplex - by the way - is only for the Delta Turbo (carb) system - mentioned in an earlier comment.

GC

Sorry, the 130TC does have a Digiplex. Im lazy and refer to them all as a Microplex. Uno turbo and Croma/Thema turbo has a Microplex too. What is the difference between a Microplex and Digiplex?

[Guy Croft]

Microplex has built-in boost retard.

GC

[NickRP]

Microplex also has knock retard...

As for the Digiplex vs. conventional distributor, I am biased. If we say that conventional distributor can be mapped, well, yes, but this involves quite a lot of effort and quite a chance of not getting it right (without knowing what exactly is wrong). On the other hand, Digiplex, with vacuum port disconnected is acting in the same manner like conventional distributor. Stock distributor is ok for stock engine. Stock Digiplex is also ok for stock engine. When the engine setup is changed, both will be inadequate. And as always, conventional distributor is always introducing error into the system, due to components prone to wear out, inferior coil charge strategy etc.

Oh, I was not aware of the specifics of the vacuum connection on 130TC Digiplex setup. On other (non individual throttles) setups, it was, of course, different. Then this particular Digiplex must have solid software filter to eliminate the pulses.

Pierro, I can also offer you affordable programmable ignition system, based on Weber Marelli electronics, together with accessories (like loom, sensors...), Windows software for programming it and lead to connect the ECU to your PC via diagnostic port. If you are interested in details, please let me know.

All the best,
Nikola Radenkovic

[Guy Croft]

Robert Girard has posted some data which may be useful here:

http://guy-croft.com/viewtopic.php?t=353

[SteveNZ]

Digiplex, or at least Digiplex 2 has knock retard. I cannot think of many cars with Digiplex (1)

[Guy Croft]

This is all getting too confusing for my liking.

I want to introduce fact from OE manuals only - as far as this is possible.
Piero's thread is about a TC so let's just stick to Fiat-Lancia Twin Cams or we'll be tied up forever. To begin with shown in the photos below are two Digiplex ecu units a 401A and a 406A one or both may be from Strada 130TC, not sure which.

What I do know is:

Digiplex 406A was used on the Strada 105TC
Digiplex 402BX was used on the Regata 1600 TC (non reversed port) (sources OE manual)

All the above mentioned ecu have 11 pin connections and both are wired (L-R see photo) as follows:

pin
1,5 tdc sensor
2,3 flywheel ring-gear tooth pickup (rpm sensor)
4 ignition positive 12v
6,7 vacant (no connection shown in manuals I possess)
8 ignition positive 12v (as 4)
9 earth (battery negative)
10 tachometer
11 coil negative

There is a photo of the OE wiring harness and coil, you can see the 2 sensor plugs, crank front pulley and fw.

To the very best of my knowledge no knock sensor was ever integrated into Digiplex, but if someone has definitive OE manual information to the contrary I shall stand corrected and amend this post.

As far as TCs go, I know that a MICROPLEX ignition (only) unit was used on the rather rare Lancia Delta HF Turbo (carburetted version) and on that unit had NO knock sensor. This system is identified in my book page 141.

I have managed to find 8 advance curves ex Fiat Strada 105TC, for the Digiplex 406A, rated from 0.04 bar to 0.6 bar manifold vacuum (1 bar = 14.5 lbf/sq in = 29.62" Hg) and speeds 0-6000rpm.

I will put them onto graphs as soon as I can, I cannot reproduce them here directly due to copyright. I imagine that, since these are mapped systems, there may well be differences in the rpm/vacuum response between engines of different cubic capacity (ie: 105TC, a 1600, may not be the same as the 130TC, 2 liter).

What I can confirm as Nick states is that the full throttle advance curve (certainly on the 406A and probably all of them) is almost identical to the standard 10 deg at idle rising to 34-36 eg total at 5500rpm used on nearly all the conventional distributors of the TC series. The part load advance can be as high as 42-46 degrees, which ties in nicely with the demand I have seen while mapping Weber Alpha FI-Ignition systems.

For the record, no more, to the best of my knowledge knock sensors (with associated ignition retard (not to be confused with the earlier manifold-pressure actuated 'boost-retard used on the Microplex) were only launched with the post 1986 series of Delta Turbo ie (the reversed port layout), Delta 4WD and 8, 16v Integrales and their cousins. These particular engines had Weber IAW fully mapped systems, with fuel injection and ignition management all from the same ecu. The Delta HF Turbo (carb) was carburetted and had no fuel management system. Croma Turbo I know little about, but be careful about confusing full fuel-ignition ecu with ignition only - since that is what this thread is about.


I hope that my 'facts' stack up and I have not made any errors; this is a very useful thread but please don't post statements of characteristics or data unless cited direct from OE manual, thanks.

GC