Vehicle turns over but will not start. Electrical issue 100% positive

I doubt it’s the ECUs but if you do find they are fried contact me with the part numbers, I have a bunch of 348 engine ECUs and can hook you up with a very reasonable price. I also have several complete wiring harnesses and fuse boxes etc.

 

Interesting. Although the fuel pump relays get power from the battery, they are controlled by the ECUs. This means the ECUs received switch-on power on their ignition key lines. Miro (m.stojanovic) might be on to something (see post #24). This could get complicated.

I don't know if you have this wiring diagram...

Ferrari 348 Engine Management Wiring Diagram

 

It is most probably just one trace blown-up (like a fuse). The traces are rather thin and one trace handles the current fused by two 10A fuses, 14 & 18. The trace is probably designed to handle the current of one 10A fuse (for one ECU) blowing at a time (the trace could be, say, 15A) but not for two ECUs causing high current at exactly the same time. In this case, The trace of presumed 15A became the fuse before 2 x 10A fuses could blow.

The repair of any blown trace would be easy, just solder a piece of wire between the existing solder points between which you have a blown trace. This is what part of the internal PC board at the back of the multi-pin connectors (between which the trace would have blown) looks like:

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To open the fuse box, you just need to grind-of the tops of two melt-riveted plastic studs marked by the two short red lines on the pic.

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Well lets think on the positive side. Looks like you found the infamous "hidden" 30 amp A/C fuse that was fried. As soon as you get the engine running you will have A/C again.

 

Do you mean the small section "2" in this diagram?

https://www.ricambiamerica.com/car-diagrams/ferrari/v6-v8/348-group/348/electrical-system-valid-for-usa-and-cdn.html

Or section "1"? That one is huge and runs across the front fender and starts to go along the passenger side.

That's infamous for melting. You may have an aircon fan problem (drawing too much current). Some replace the fuse with a resettable circuit breaker, but the cause of the overcurrent should be investigated first.

 

It is a good advice but, luckily, the melting of the fuse is in most cases caused by resistance, developed between the fuse spades and the sockets, due to corrosion (the boot/trunk can accumulate quite a bit of moisture during humid days). The contacts then start acting as heaters melting the socket and the fuse. Overcurrent in the blower motor would, I think, just blow the fuse. A "Maxi" fuse (still 30 Amp), or other type of physically larger fuse, solves the contacts overheating problem.

 

I wired in a bullet fuse shown circled in red.

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Looks ok, but before you put it back together, if you have a magnifying glass, look for cracks in the soldered connections. Make sure the fuse and relay pins are actually attached to the solder. I've found micro cracks on some circuit board connections which weren't visible.If you're really keen, you could put fresh solder on all the connections. Some of them look a little rough.

Is that a track running around the entire edge of the board? How does the track look on the hinge line?

 

The PC board is double sided so the blown link could be on the side you cannot see (bad luck). I have detached the side of the PC board from the plastic panel where the fuses and relays are but not from the side where the connectors are (seems impossible). You can start a tedious job of first identifying/marking on the circuit diagram which pins of one connector are connected to which pins of another connector (this is for the lines that just go through the fuse box). Then, using an ohmmeter, check whether there is continuity between the relevant solder points on the PC Board. The first check I would do is check the continuity between the solder point of the blue wire from the ignition switch and the two solder points to which the yellow and yellow/black wires (that go to the ECUs and the ignition coils) connect. If you find no continuity there, you can bridge the solder points with a length of wire. Or you can just buy another fuse box, once you test with a new ignition switch and confirm that the problem is not there.

This picture shows one fantastic example of what can be done (work done by one of the members here):

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Good point. I thought it was like a traditional circuit board where the tracks are fine lines with some thicker sections, but being a power board, the non-current carrying sections are probably thin tracks.

I assumed the thick brown sections were typical non-conducting circuit board material, but if they are copper, then indeed they will be the tracks.

 

The "green lines" are not any tracks, just space between the copper tracks. What you see as green are parts of the plastic base plate on which the copper tracks seat. All solder points not soldered to the copper tracks on the side of the PC board you see but are in the "green" areas, are the points that are soldered to copper tracks on the other (inner) side of the PC board. The grid of the copper tracks on the inner side is very different from the copper grid you see.

 

Is it possible to ohm out each pin to the connector side to try and find the broken trace?

I had some issues like this on the ECU in another car where the solder points on the board were slightly cracked.

I spent some time and re-heated each joint to reflow the solder.
That worked and is a common issue on that particular Bosch ECU (1980) .

In fact my speedo died on the 355 this past spring and I did this and it fixed it as well.

 

I had another look at my open (waiting for repair) fuse box. The PC board is actually not double sided but there are two PC boards placed on top of each other.

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James, since the engine won't run, maybe you could check only the engine-related circuits of the board with an ohmmeter? See the top right hand corner of the diagram on the link below:

Engine Management Wiring Diagram

Note the small graphic in the top right hand corner with the connector identification. Unfortunately, the diagrams don't show the pin numbering (1~xx). You might have to experiment. e.g. the orange wire on connector (E) may be pin 2 or pin 11 and it may go to pin 1 or 12 on plug (F). But once you have established the sequence on the diagram on one side, the other's on that side should follow. A better solution might be to sit the board in the car and put the plugs temporarily in place and match the wires to the diagram. If you could do this, and then mark the numbering on the diagram, it would be of benefit for others.

(EDIT: Commonly, the pin numbering on Ferrari diagram relay panel plugs is top to bottom, left to right, so that would be a good starting point)

The ignition switch is also shown on the diagram, so you could also check the (red and blue) wiring from the 8-pin ignition plug to the relay panel.

I would take your time with this. You don't want to damage your vehicle further. On first look, the board looks ok, so the problem may be elsewhere.

 

With the new ignition switch, if it does not solve the problem, you can easily check whether the ignition switched supply (from the thick blue wire) goes through the fuse box - disconnect the 3-pin connectors from the coil packs (left and right), switch the ignition to "on" and check whether there is 12V between the middle sockets of the disconnected connectors and the ground. If you don't have a multimeter, you can use a small bulb (5W) connected between the middle sockets and the ground. If there is no voltage (12V) present (or the bulb does not light-up), the fault is in the fuse box PC board, i.e. blown trace between the blue wire coming from the ign. switch (to the connector E) and the yellow & yellow/black wires of the connector F (see detail from Ian's diagram below).

Bring the plug to the socket E of the fuse box (the sockets are marked A, B, C ...) and determine to which pin of the socket the thicker blue wire connects. Do the same with the socket F and find out to which socket pins the thicker yellow & yellow/black wires connect. Then, transfer the "information" to the PC board side of the positions of the socket pins identified and mark them - blue dot for the blue wire, yellow dot for yellow and two dots, yellow and black for the yellow/black wire (this suggestion is only if you want to do fancy marking). You can then check the continuity between the "blue" solder and the "yellow" and "yellow/black" solders on the PC Board. If this re-confirms that there is no passage of power between the said solders, you can simply just solder a piece of wire connecting the blue solder to the two yellow solders. Then, give it a try. For the first test, I would put 5A fuses (instead of 10A specified) in the positions 14 & 18. If they blow instantly, the fault somewhere may still be present. You can then try with 10A fuses hoping that the 5A fuses blew just because they were under the current that flows there at ignition "on" or they may also blow due to the fault somewhere.

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I have identified the "blue" solder and the "Yellow" & "Yellow/black" solders on my PC board. The blue is no. 7 solder counted from top (of the picture below) and the yellows are nos. 2 & 3. Just get a multimeter and see if you have continuity from the blue to the yellows. As you will note, these pins are soldered to the lower (inner) PC board as they are not connected to any of the copper traces that you can see (they are in the "green" areas of the top board). If you have no continuity, and as the repair of the inner board is not really possible, just solder a piece of wire from the blue solder to the two yellow solders. Since the two yellow solders are anyway connected to each other on the inner PC board, you can have one end of the bridge-wire stripped a bit longer so that it can be soldered across the two yellow pins/solders. Use a piece of wire as thick as the blue wire in the connector E.

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Ha anyone bothered to check the replacement ignition switch for continuity in the ACC, RUN, and START position?