Mondial DigiPlex MED 801A Testing

Can't say that I've ever seen such a F document for Digiplex -- because there really isn't any place to test stuff. You've got the input signals from the RPM (aka Tachimetric) flywheel sensor and the two TDC flywheel sensors (but both of those have to fail to take out both banks), and power and ground. And the outputs are just the signals going to the coil primaries (so those are switching or they are not). There's a good schematic on page D1 of the 281/83 Mondial8/QV WSM, and there should be one in Section 3 of your OM. (Give a shout if you need a copy of the 281/83 WSM.)

They did write a better document for the Microplex system because on that system (with the Power Transistors separated out from the main single Microplex ECU) there are more place to measure things. Microplex use the same flywheel sensors, but has just one TDC flywheel sensor (so the information about the flywheel sensors in Service Bulletin 80-28 would also apply to the Digiplex flywheel sensors). You can get a copy of that Microplex Service Bulletin 80-28 here:

https://www.dropbox.com/scl/fi/p8jqhfui433o89imz7xs7/Service-Bulletin-80-28-microplex-ignition.pdf?rlkey=tguaco5cg0324ug1v0ha8b40z&st=49jbl9mz&dl=0

PS IMO, it's better if you just keep it all in one thread, rather than starting a new thread for every sub-topic, in your quest to fix your Digiplex ignition system.

 

No, that's just a rather bad translation -- that "on/off switch" is a thermoswitch mounted in the coolant expansion tank which is "open" when cold, and causes the Digiplex ECUs to retard the ignition timing map by 5 deg IIRC. Then, when "warm", it closes and "tells" the Digiplex ECUs to remove the extra retardation. But, regardless of the "on/off switch" state, there should always be spark.

 

These are for a 308 QV but I would expect your car to be similar.

Basic wiring of the digi.

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If you have a diagnostic plug, check the manual but for the 308 QV it is as follows.

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What you need to do is check that crank sensors are generating the correct signal which you will need a scope for.

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Then you need to look at the "ignition trigger' which fires the coil. Below are examples of a bad trigger signal, left, (due to a carbon track in the distributor) and a good signal on the right. (A bad signal may have a different appearance than the one shown).

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These can be check while cranking the engine.

 

The only single component I have seen take out both ignitions is the RPM sensor. It is easily diagnosed.

 

A related question which I should know the answer to, but don't -- We have a Bosch 7mm Opti=layer mag core ultra-premium wire running from the coils to the distributors. How much resistance should we be seeing between the connector on the coil end to the spring loaded contact in the center of the distributor cap??

p.s. FasterIsBetter II is my grandson. I'm glad to be teaching him to love auto restoration. He's very enthusiastic! !

 

F of your era are designed with a spirally-wound fine-wire internal conductor in the spark plug wires, and typically have a resistance of about 700 Ohms/foot IIRC (and a non-zero inductance). That said, I'm having a vague recollection that of some of my prior coil wire resistance measurements being closer to 2K Ohms (which is a little higher on a per foot basis). What you definitely don't want is a wire with a very low resistance (i.e., very low impedance) = hard on the output transistors of the Digiplex ECUs.

Are you also presently now without the stock resistive spark plug extenders?

 

Steve, Thanks for getting back to us on this. Your input is extremely helpful as always. Two prior owners had worked on this car and changed a number of things. We've been slowly sorting what was done and trying to make sure things are actually working. Here's where we are kind of at with what we've done:

One of the prior owners set up a separate wiring run for the fuel pump and the starter. It looks like he tapped into the white wire under the steering column and connected that to his make-shift starter circuit. We can turn on the key and the dash and other stuff comes alive. The prior owner's mechanic told us to turn on the key to the run position, turn on the fuel pump and then hit the starter switch under the dash that had been installed. We do that and the engine turns over nice and strong (we put in a new battery; the old one was dead). But it doesn't start.
We have tested at the spark plug leads and have been getting no spark there at all when we kick it over.
We tested the wires coming to the coils and we do seem to be getting power there.
We tested the leads from the coils to the distributors and they tested out at 73K ohms (yeah, 73,000). Did a little research and it sounded just way too high. So we got a couple of new coil leads and they test out at more like 9K, within the limits that seem generally acceptable for a 16" piece of wire.
We had new distributor caps, so we changed those as well and all leads test good with wire resistance within limits, about 7.5K per foot.
Still no spark at the plugs.
My son picked up a sensor that's supposed to pick up magnetic field activity (Hall effect?). When held to the coils when turning the engine over, the sensor shows activity/pulsing at the coils, but no spark.
On other thing to mention, when we turn the key to the run position, something in the passenger foot well is clicking like crazy. I haven't dug in there yet to see what's going on. Any idea what that might be??

So anyway, any additional thoughts you might have would be greatly appreciated. Any suggestions on where we go from here? I feel like if we can get it started, other projects will fall into place and we'll be okay and have some fun with this car.

Many thanks as always,
Steve W

 

That you're up a creek without a paddle? Seriously, that is some major, major molestation.

There are quite a few electrical gizmos in the passenger footwell on a US version, but nothing that should be actively clicking with just the key "on". There is a tachometric relay in there that receives the tach signal (i.e., the signal from the minus side of the coil primary that should be switching from ground to a positive voltage at each firing event) and whose function is to disable the air injection system at engine speed above 4400 RPM when cold. If this tachometric relay is clicking a lot (when the engine isn't even running) = that could be a sign that you have a very strange signal on that coil connection for some reason. Also, the passenger footwell is a common area to hide added electrical stuff so wouldn't hurt to see what else might be in there, and identify what is "clicking".

Do you have a link for this device to describe how it works and what it outputs? Does the activity/pulsing correspond with the rate that firing events should be happening during starter motor cranking, or is it just a "something is happening" indication?

Would still say that confirming the RPM flywheel sensor signal and TDC flywheel sensor signals are reasonable/correct per SB 80-28 is a needed diagnostic step.

 

My courtesy light timer under the passenger foot board clicked when ignition turned on. I simply unplugged it for now. It was also the source of the parasitic power draw when ignition off.

 

Thanks for this - where is the "ignition trigger" located and how do we test it?

 

It's the yellow/black (5-8 bank) or the green (1-4 bank) wire connected to the coil for the corresponding bank. Again, you need a scope to test it. Test it by connecting the scope between it and ground.

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Here is a video:



Here is another video I make with some explanation.You see when the ignition is turned on the voltage jumps to 12V. Then once started (or cranked) it shows the intermittent grounding to create spark.

 

Steve, where can I locate a copy of SB 80-28 and what equipment do we need to test the sensors?

 

Johnk, in the last video you have a small scope that you connected. Any info on make/model and source?? Much appreciated.

 

The scope is a hand held unit. Diymore DSO 152 Handheld Small Oscilloscope. https://www.ebay.com/itm/356411998356?

Here is 80-28.

 

John also posted it, but I put a link to it in post #2.

A multimeter that can measure resistance and AC voltage would be the minimum required (if you don't have access to an oscilloscope -- but you can get one on amazon for about $40).

 

750 ohm is in the ball park. 1 ohm sounds like you have a short in the wiring somewhere. The pins on the diagnostic connector tell you which sensor is which, bank 1 or bank 2. See my diagram in post 5. Also the wire colors on the back side of the diagnostic connector. Bank 1 has the green wire and bank 2 the yellow one. But don;t confuse the yellow sensor wire with the yellow 12V wire. Again, I'm assuming the wire colors on you car are then same as for my 85 QV.

Now, if you need yo replace one of the sensors I don't know about a Mondial 8, buy on my QV there are real pain to get to. But before replacing what appears to be a bad one I would disconnect the sensor where it connects to the wiring harness and check to see if the harness has a short and also recheck the sensor resistance. If one is bad you need to replace it. They aren't expensive. Available on Amazon and Ebay: SEN8D RPM/TDC Sensor SLight problem though. The mounting holes on the new ones are spaced the same as the old ones so you have to file them to fit.


https://www.amazon.com/dp/B00D76G09Y?ref=ppx_yo2ov_dt_b_fed_asin_title

 

Looks like the buzzer for some function (seat belts? or maybe low oil pressure? or maybe key-left-in-ignition?) -- the "musical notes" on the outer case are a clue :

https://www.ferrariparts.co.uk/part/ferrari/60870100

They got a little fancy and put the fuse panel relays and the passenger footwell stuff all on the same SPC figure page -- it's item 25 here:

https://www.ferrariparts.co.uk/diagram/ferrari/mondial-8-usa/116-electrical-board

(These SPC figures at MCP can be a good resource for you to use for part names/functions, and they often have photos of each part.)

 

Even more modification would not be my first choice, but that's just me. David Feinberg can replace the internals of your Digiplex ECUs with more modern electronics (and a better ignition map) -- the last information that I had for how to contact him is here:

https://www.ferrarichat.com/forum/posts/149935410/

He could also test your existing Digiplex units, but, once you've paid for shipping and testing, IMO, it would be best to just have him do the updating anyway (even if they are working).

However, I'd still be very suspicious that both of your Digiplex ECUs have failed...

 

What about Brian's comment in post #6? Have you tested the impedance of the rpm sensor? It's the same as the crank sensors.

 

This is the same relais for wiper motor if it connected directly to the fuse board. You can open it and clean the contacts eventual it can help.