Look familiar? What is appears to be happening is that the coil is discharging before the full voltage is built up. You likely have a problem on the high tension side. A secondary path to ground that is preventing the coil to build up sufficient voltage to arc across the plug gap. The exponential decay indicates that the coil is not discharging across the spark plug gap but through a finite resistance. Image Unavailable, Please Login
Just a little follow up. It is strange that it is happening on both sides of the coil (i.e. no spark on Bank 1 at all). But check the spark plugs wire, plugs, etc. Any chance water got into the bank 1 plug wells? Pull the plug wire off the coil and measure the impedance between the coil end of the wires and ground. They should all measure open circuit. If any measure a finite resistance, even if it's pretty high, it's probably the problem. If they all check, then maybe it is in the ECU but I would go there first. One thing that does bother me is that when the voltage goes to ground it stays there. The slanted upwards part seen for bank 2 is due to the increase in current flow through the primary side of the coil as it charges. You might want to look at the voltage on pin 1 of the coil with the scope too. It should stay fairly constant at 12 V. Image Unavailable, Please Login
Ian, I don't have the 5.2 wiring diagrams. Is the 12V to pin 1 of the coils supplied through the ECU or is it directly connected to the battery through the ignition switch?
Yes, something like that. The part of the graph below the horizontal line actually shows the quality of the connection of one side of the primary windings of the coil to the ground (the other side being permanently at +12V). Obviously the connection (switching by the transistor) to the ground is not "sharp" and not full. This, in turn, does not provide for the full rise of the magnetic field in the coil and, when the primary current is cut-off, the weaker magnetic field will produce weaker flyback voltage spike in the coil primary as well as insufficiently high voltage in the secondary windings. The poor switching to the ground, if there is no fault in the transistor or its driving circuitry, could be simply due to a deteriorated solder on the transistor collector or emitter or elsewhere on the PC Board along the path from the transistor to the ground provided by the ECU's circuitry.
Just in case Ian is already sleeping - I had a look at his diagram and it shows that the +12V on Pins 2 (not 1) is ignition switched. Pin 2 goes to one side of both primary windings in the ignition coil. The other sides of the two primary windings go to their respective switching transistors inside the ECU which switch them to the ground.
I believe so. That's the part I haven't got fully mapped, but I made some educated guesses on how it was hooked up based on simple wiring checks and the wire colour differences between my 5.2 car and the 2.7 wiring diagrams. 5.2 Ignition/Injection As I may have mentioned earlier, when Ferrari converted the 2.7 to the 5.2, they tried to change as little as possible. A relay removed here, a wire repositioned there, etc. It was relatively easy to figure out what they did. See pin 2 of plug 41090.
Thinking a little more. There are two issues. 1) the exponential decay, 2) the flat bottom ground of the signal. The first definitely indicates the coil is discharging though a finite resistance, not across the plug gap. Why? Either a problem with the secondary wiring as I initially stated, OR the secondary voltage never rises sufficiently to bridge the gap. What would limit the secondary voltage? Insufficient current through the primary winding. What would cause that? 1) Poor ground switch, 2) Drop in supply voltage. The scope signal shows that the voltage on pin 3 when switched to ground remains at ground when it would be expected to rise slightly as the coil charges. This seems to indicate the supply might be being pulled down which suggests some excessive resistance on the supply side which might also account for the exponential decay when the switch opens. This is why I suggest looking at the voltage on pin 2 with the scope and compare it for both banks.
Grant said he found a pushed back pin on the 12 volt supply... https://www.ferrarichat.com/forum/posts/146615483/ Should we still be worried about it. He said he had 12 volts on his subsequent checks. Maybe the wires are damaged (inside the insulation) and there is only a strand or two supplying the current.
Yes, but he measure the 12V under static conditions when the car was not running. There could be significant resistance between the battery and pin2 and with pins 1 and 3 ungrounded you would still measure 12V. Need to compare pin 2 voltages on a scope trace while running.
Good point. Just for easier understanding, I attach a simple diagram showing one ignition coil and the ECU "relationship". The +12V supply to the coil, shown to be coming from the ECU, is actually ignition switched on the 355. Image Unavailable, Please Login
Going to go out on a limb here and say I'm leaning more and more towards the 12V supply, only because everything else requires multiple, simultaneous failure.
It is easy to check - connect a piece of wire to the line to Pin 2 and, after switching the ignition "on", connect the wire to the "+" terminal of the battery then crank.
Small diversion... My engine basics are poor... Looking at your diagram, Miro, do the coils have to be hooked up to the spark plugs in inboard and outboard pairs to make the engine operate correctly? On the F355 2.7, the spark plugs with component numbers 02500 and 02501 are connected to one coil, 02502 and 02503 are connected to the other coil. I assumed the sequential numbers reflected cylinder numbering 1~4. The F348 diagrams do show actual spark plug numbers (making it easier to see). The only official-looking wiring diagram I found for the 5.2 stops at the coil pack and I don't want to pull my car to pieces to find out Might there be a common device in the ECU which triggers the two transistors for the 2 coils on that bank? Grant, have you actually bought a new ECU or are you still hopeful for a cheap fix?
Just 1 on each but since my timing light shiwed no spark on bank 1 at all i did not th8nkit necessary
Yes they are i just used slow motion but you see the videos speed up near the end. I am also assumming the coil that was good 4 years ago is still good. Its obviously been dropped because the plastic surrounding 1 plug connection was broken when i took it out. I did not menti9n this before because i was possitive it was good but with this signal now i am unsure
I can confirm that it is direct because the 9 pin plug on Ians diagram supplies 12 volts. Just a theory but what if the 12 volts supply will not supply enough current to bank 1 to allow it too fire properly when grounded by the ecu?? I could put a meter on the supply line for f you all thoughtit would help?
John i was busy at work so I just started to read your email just now but kinda went over my head. Once I understand a bit more i will respond
John is suggesting that instead of a meter, put the oscilloscope on the supply (pin 2 of the coil). This will pick up any unusual rapid drops in voltage with the engine running. I guess pin 2 of that 9 pin plug would be the same (if it's easier)
