Digiplexes --- several on Ebay currently

One reason; US emissions. The timing curves for the US-spec cars are horrible in terms of performance.

 

And detonation. Ferrari has always run scared of it. One reason so many of the cars had very conservative compression ratios on the pre detonation sensor cars.

Ever wondered why the cars went from 8 something to 1 to 11 to 1 in the 355?

 

Point well taken. I figured that they were (also) paranoid about NOx emissions which are almost directly tied to combustion temp. Based on the combustion chamber design, I didn't really even consider detonation to be an issue. Then again, how could it be at the low ratios prior to knock sensors...

I do find it quite amazing on just how much both the QV and 2-valve engines "come alive" with just a 1 point bump in compression.

 

Their concern about detonation goes way back. Even most of the old comp motors only had around 10:1.

American street V8's were in the 12's for a while.


But there is no question, smog laws were an issue too. Lower compression and conservative timing.


My 328 is 10.7:1 with stock timing and California pump gas works great in it.

 

@Adrian,

after switching to the electromotive XDI ignition set up five ears ago, I have 2 digiplexes med801A as left overs - one is (almost) shot, the other still in working order

sofar, I saved them although I`m pretty sure I will never use them again -
on the other hand, if there is a chance that the modules can serve a nice project of someone who knows his stuff ...we can give it a try
and maybe, in the end you will not only find out more secrets of those boxes but also I end up with a repaired unit

if you send me your address via pm, I can have both units shipped to you by next week

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Fantastic, thanks! I'll send you my contact details as pm.

Danke,
Adrian

 

For the fun of it i did a quick draft design of a new 801A/802A electronics board with a programmable coil output ignition driver, status led's for RPM/TDC/APS/Ignition for easy fault finding and an USB port for installing custom maps. Just a doodle right now but i'll probably build one or two to do some software development and testing on it.

I noticed that the connector terminals 4, 6 and 7 of the original MED 801/802A are not connected in the 308 GTB wiring sheet, although internally they are wired to the PCB. Does anyone know what the terminals are for?

Adrian
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Terminal 6 is connected to the coolant thermoswitch on the US i-2V (801A) -- see the note on page D5 of the Mondial8/QV WSM 281/83 that indicates that the ignition map shown in Fig 6 is for a "hot engine" and the whole map is retarded by 5 deg "with cold engine" -- one of the maps on page D5 is Fig 6 (801A US i-2V) and the other is Fig 6/1 (805A US 308QV), but they mucked up the multi-language labeling at the bottom so I'd guess that Fig 6 (801A) is on the left, but don't know that for sure. Since no coolant thermoswitch is present on euro i-2V (802A), terminal 6 is not used.

But are you saying that you have a single "308...wiring sheet" that applies simultaneously to both 801A and 802A?

 

Dave, yes 6 & 7 could be for bench testing but then again it does not seem to be documented anywhere and factory testing would have direct access to the PCB test points. Hmmm..
A Fiat (Uno?) Digiplex wiring diagram i found somewhere in the net shows terminal 4 as the connection point for the economy meter, so that would make sense as terminal 4 supplies the RPM signal from terminal 3.

Steve, sorry that should have been sheets. Terminal 6 wiring is not shown in the ignition chapters (page 71 of the 308 GTB and GTBiGTSi US owners manuals) but i found it in the circuit diagrams of the 308 GTB and 308 GTBi/GTSI owners manual after looking again, thanks!

 

Maranello parts uk currently have new ones on special at the moment,(part 115977) priced at £369. ($560) For those with Euro cars....

https://www.ferrariparts.co.uk/PagesExternal/ManagerSpecials.aspx

 

Great, thanks for checking!

 

Simply AWESOME!!!!!!

 

All, thanks! Have added an input for terminal 6 for later use. Will spend a bit more time to see if the approach is feasible and then create a new thread if there is interest. I need to do a bit of research to see what components make sense and can be easily sourced.

Adrian
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I am planning to replace my digiplexes with Nick's electromotive units and I just read Rifledriver's comment that Ferrari left horsepower on their US models. I have a 1985 Calif 308QV with the 805MEDs, therfore will I notice any power increase with the Electromotive units?

Joe

 

Plenty of us would love a reliable plug and play adaptation of the existing units that would extract more performance. Definitely a market for it 'round here.

 

Wow, that is a great photo that preserves some engineering history of the changeover from leaded components to surface-mount components. Can't fault them for trying to keep the cost down (a via-less PCB?) in this application, but surface-mounting leaded components was ballsy -- no wonder they figured out that they needed to pot it in cement

 

Stay tuned...I've heard several rumors that a well-respected supplier will be marketing exactly that in the not too distant future.

 

The PCB in the MED801 actually isn't a PCB at all but a ceramic substrate hybrid Marelli deployed hybrids in the precedessor of the Digiplex mid to end of the seventies, and then opted to do a full hybrid with thick film resistors and SMD capacitors for the Digiplex 1 & 2 series. Except two transistors, all other discrete parts are in wire-through packages (but with surface mount wires), an interesting mix of packages and technologies.

Marelli went back to wire-through PCBs with the Microplex and the more complex IAW series. Ceramic hybrids are good for small and low volume custom circuits but not really that robust and economically viable in a size as used in the Digiplex units.

Quite forward thinking engineering for that time though.

 

A Ferrari shop down in Orange county sent out six digiplex to a place in Arizona that he claimed got it all back and was all repaired. I'll see if I can find out who and where in AR. repairs Digiplex.