Mondial DigiPlex MED 801A Testing

Hi Max,

I'd retest the sensors. The first 2 are probably ok but the third is not looking good. Make sure you have a good ground. The problem is that those little scopes have limited sampling rate and if the time sweep is too long they miss the voltage spikes. Check out my video below. The voltage scale is 10V/division. The time sweep starts at 5 ms/ and then I change it to 10ms/. You can see how the scope trace changes with a 10 ms sweep. If I make it longer it would look like you first 2 videos. You may have to experiment with the time setting to get a good trace. Mine were with the car idling at 1000 RPM. If you car cranking figure 200 RPM which suggests about 25 to 50 ms scale.

If the rpm sensor is bad at lease it's the easiest to replace.

 

Those voltages are OKish. What you've got wrong is the time base on your oscilloscope is way too slow (I've got that same little FNIRST unit). You need the middle balloon of the five balloons at the bottom of the screen to be something like 10mS or 20mS -- see page 15 in the Instruction Manual. The balloon labeled "5" is the horizontal time base for a major division. Using the thumbwheel at the top left of the unit is how you highlight each balloon -- hold the thumbwheel to the left until balloon 6 goes blue, then release. Then hold the thumbwheel to the left again until balloon 5 goes blue and release. Then use the up-down arrows to change the value in balloon 5. Use the same method for the other balloons as necessary/desired, and when done use the thumbwheel to the right and release as necessary to get back to RUN. Balloon 3 should be something like 2V or 5V, balloon 4 = 1X, balloon 6 = not sure but either AC or DC coupling should be OK. Fiddle with this until you get a reasonable looking signal for the Tachimetric Sensor. The TDC sensors are more difficult because the pulses occur very infrequently.

With that said, just use your multimeter set to AC volts as an initial check to make the same measurements. The Tachimetric sensor should have an output like greater than 1.5V AC during starter motor cranking, and the TDC sensors should have an output like greater than 0.1V AC during starter motor cranking. Then you can try to figure out that user-hateful FNIRST manual and how it works -- it's truly horrible .

 

Mistyped -- should've written "top right of the unit".

 

No (all those voltages are quasi-reasonable). Now that you've got the oscilloscope, you could measure between terminal 1 on the coil(s) primary to ground as shown in John's post #13 -- if things are working, it should look like his "Good" photo -- however, the firing line (vertical spike) can go up to ~350V, and I'm unsure if the FNIRST unit can handle that (so check into that please before doing this). This is a good video to watch:

https://www.google.com/search?client=firefox-b-1-d&q=voltage+on+coil+primary#fpstate=ive&vld=cid:18ebe188,vid:7_Wio5t6XEo,st:0

If the input signals are all good, but it's not working = not a good sign for the Digiplexes (and this is where it would be nice to have a known good Digiplex to swap in for a test). Have you had a look inside the distributor caps to see if the caps/rotors/buttons are in reasonable shape and are not filled with oil?

 

If can handle it. Repost form my post #17:

Triger signal.

 

Wait a minute. If there is no trigger the voltage at either coil terminal should remain at 12V with the ignition on. If you are not getting 12V relative to ground something is wrong with the test or you aren't getting power to the coils, and possibly to the digiplex units. The yellow wires in the figure below are the 12v lead, straight from the ignition. No fuses or relays. You could have an ignition switch problem.

Ignition off: zero volts at the coils.
Ignition on: 12 V.
Cranking: Trigger signal, jumps from 12v to ground (on the ground side of the coil) followed by the spike and then back to 12v, and repeat.

You might try connecting the yellow side of the coils directly to 12 V. That should also back feed the digiplexs.

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thanks Johnk. We are getting 11.2-11.5V at those yellow wires that run straight in from the battery while the battery is showing 14V. So we seem to be losing something from the front to the back of the car in that line with no relays or fuses in between, as you say. When you say run 12V to the yellow, do you mean just run another wire straight from the battery to the yellow wire going into the first coil and then try running the starter? Or something else?

 

Are you saying you are measuring 11+ V on the yellow wires at the coils. If that's the case something doesn't make sense.

Yes. that's what I mean.

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Just rehashing. You seem to be doing everything right. Looks like the scope is in DC mode, which is correct. With factory wiring and the vertical scale set to 10V/division, you should see 0 volts at the coils with the ignition off, then it should jump to about 12V when the ignition is switched on (not cranking). With a jumper, you would see 11+V all the time. (Make sure you have a good ground.) If that happens and then when cranking nothing, it's not looking good for the digiplex units. I'm not saying that 100%. The other thing would be the check for continuity between the coil trigger wire connections at the coil (yellow/black or green) and the digiplex connector pin.


Has the car ever run since you bought it?

Perhaps Steve may have additional input.

 

That's normal. +12V power from the key and terminal 15 at the coils are connected together by the fuse-relay panel. See the schematic that John posted in post #34 -- the tops of fuse A and B are connected together. When you apply +12V directly from the battery to terminal 15 at the coils with another wire = it powers up everything that key "on" powers up. (Although the schematic that John posted may be for a 308 so how that connection is made on a Mondial fuse-relay panel is probably different.)

 

That's great. Like Steve said, that connection directly to the battery back feeds a lot f things. Does the car have any type of immobilizer? If not, a wiring problem or it may be that you have a bad ignition switch. They can be found pretty cheap. https://www.ebay.com/itm/392883160790?

 

Hi Fasterisbetter II and I have an update and a new question... We got the car to start! We were not getting fuel through the injectors and we took off the air filter to get better access to the fuel distributor. We ran the starter and noticed that actually the air flow sensor plate was not opening. We then pushed it in a little manually and the car started! Below is a video of the testing. (We were able to get spark running the wire to the coils straight from the batteries as discussed above, so we still have an electrical problem, but this problem first now...)

This air flow sensor plate seems to be the main mechanical issue. Upon inspection it looks like the plate is sitting too high, according to page D30 in the shop manual, it says the plate should not sit "outside the short cylindrical part at all," and it is definitely sitting at the level above that in the upper conical part. Would this cause the plate not to open when the starter is run? If so, the shop manual makes it sound very tricky to punch the stop pin in to lower the plate. any advice?

 

To much control pressure. Try cleaning the WUR inlet ports (pour some carb cleaner in the port, if it fails you will have to open it).

Do you have a k-jet test gauge?

 

thanks. we will try to clean the WUR, was trying to avoid buying a k-jet test gauge but maybe we'll need one... We did find some cracked air hose lines that we replaced but that didn't solve it.

 

We got the WUR off and will clean it (having trouble getting the fuel cell screws out right now) and fix up with the replacement part kit. Also got the k-jet test guage so we'll test control pressure when we get it back on. I'm also curious, it appears from the Bosch K-jetronic book that the air flow sensor plate should be sitting at a slight angle with one edge slightly below the flat opening between the two cones. Ours sits entirely in the upper cone by about 1mm. Assuming the WUR is working properly would you expect that to still create the stalling issue at cold start or would you expect that positioning shouldn't matter and the plate should still properly drop? I'm wondering because it seems like adjusting the plate's zero position by hammering the adjustment pin is a very hairy proposition so I'd rather not do it if unnecessary...

 

Don't disagree that moving the pin to reposition the airflow metering plate in the funnel can be tricky, but use the figure in Chapter D of the 281/83 Mondial 8/QV WSM to determine if you need to do so (but it sounds like you do need to):

https://www.dropbox.com/scl/fi/twng41f9fpi3ipww7q95v/Mondial8qv_workshop_281-83.pdf?rlkey=5sgpj4yz33jepzrec4x8lcwel&st=9n9fgpcr&dl=0

 

Thanks - we tested the pressure this weekend. System pressure 5.1 bar so seemed good, then control pressure only dropped to 4.8 bar when we opened up the valve. So we have way too much control pressure as @raemin said. We tried to clean the WUR but can't get all the parts open so we are going to send to CIS Flowtech. Will report back... I also have some wiring questions on the wiring bypass we have and how to restore the fuel pump wiring to original. Any suggestion on whether we should start a new thread for that or keep this one going?

 

Disasembling the WUR is easy. If the point is to clean the wur, once ÿou've got access to the back of the inlet port, just clear the crude with MEK or acetone. Adjusting pressure a bit more complex, but not horrendous. See photos here:

https://www.ferrarichat.com/forum/threads/what-did-you-do-to-your-365-gt4-2-2-400-412-today.488990/page-9#post-148136419

And this thread:

https://www.ferrarichat.com/forum/threads/ferrari-412-cis-injection-experts-opinion-needed-low-power-weak.690904/#post-149597914