Hi all, I'm hoping someone here has the answer I'm looking for. Does anyone know what the various prongs on the Diagnotic Plug actually connect to? The wiring diagram that I have (488/87) seems to indicate that only 6 of the 8 positions are connected to anything, and from probing them I can't tell that the manual represents what is on my car. Also, I'm not positive I'm understanding the orientation of the plug, i.e. which wire is which. Alternately, there is a diagram floating around here (a Powerpoint file that is attached) that seems accurate both in appearance with the staggered center row missing it's center prong as well as the hot and ground, which I tested. I thought I would be able to determine connections between this diagnostic plug and the connection to the ECU by checking for continuity: If I connected to one of the TDC prongs (3 or 4?), it should show continuity at slot 1 or 2 at the ECU and an open circuit to the other slots at the ECU. When connecting to prong 3 I got continuity at the coil connection slots on the ECU as well as slots 1 and 2, so that idea seems incorrect. Note that the connection to the ECU was entirely off, so it wasn't connecting through it. So--does anyone know what sensors prongs 3-5 are connected to on this diagram? Also, its numbering sequence is different from those shown in the manual which is numbered in 3 stacked rows, left to right 1-3 above 4-6 above 7-9. The car wouldn't restart after a recent drive and had to be brought home on a flatbed. I suspect there may be a problem with a connection to the TDC sensor, but can't confirm that. I cleaned all the wiring connections in there and it started up fine today. I don't know if it was dirty, wet, just needed a jiggle, or something else. I'd rather know what the issue is so I know that it is permanently fixed. Thanks for any insight on this. Peter Image Unavailable, Please Login
I made that diagram from the wiring diagram and testing so if your research tells more let me know and I will update it. If it was me I would first verify if the fuel or ignition system is not working. An inductive timing light works good to verify spark. Check grounds on multi plex unit and some of those multi-pin connectors. Strain on the cables can make them loose contact. On mine, I have been able to apply pressure to the cable bundles and get the the car to shut one bank or the other down. Good luck. Mark
In the wiring diagrams, they don't always show every wire in every connector on every page (although I would agree that they sort of made an error here because the "missing" wires don't appear on a different page in 488/87 -- I note that they did this a little better in the US 328 wiring diagram 440/86). The ignition schematic in the corresponding (euro) Mondial 3.2 OM 474/87, Section 3, "ignition" is more complete, and (correctly) shows those power and ground wires: Image Unavailable, Please Login Have you tried just measuring the resistance between terminals 1 and 2 in the unplugged ECU harness connector to confirm/deny the TDC flywheel sensor resistance - i.e., why mess around with the diagnostic connector? Also, they may have just made an error in the drawing of the diagnostic connector pins on the diagram, and you never know which side of the connector they are showing on the wiring diagram (so this can "mirror image" the pin pattern) -- if you were really measuring on pins 1 and 6 (instead of 3 & 4) you might get some weird results. I don't really know they made any errors here, or not, for sure, but unless you can read the actual molded pin identification numbers on the diagnositc plug itself, I'd be skeptical -- and even then I wouldn't be 100% sure
Guys--thanks so much for your help, it really puts the pieces together. I have been testing through the ECU connection as per Ferrari 328 Ignition ECU Testing (Microplex MED 806A) by Carl Rose, Brian Crall, & Mark Foley-(Many thanks to you as well), but only as far as those tests that can be done without back-probing the connection. The Mondial ECU location looks a lot less convenient than that of the 328; it's in front of a rear wheel with the connector facing inward, so I don't think I could safely or accurately test without a lift. The resistance across the TDC sensor is correct, but I couldn't check it's operation when running. I was also told that a shorted line to the TDC sensor may read as having correct resistance, but that it would not generate a similar signal. I hadn't realized it before, but the pin numbers are cast into the plastic and match the numbering used by Mark and shown on the diagram Steve provided. Just for jollies, I've attached the relevant section from my wiring diagram, which just doesn't match my car. The car is now running, so my concern is not the TDC sensor as the wiring between it and the ECU, or from the ECU to the coils. I think I'll check it to establish a baseline, in case the car dies again. And again, thanks so much. I couldn't own this car without Ferrarichat and contributors like you. Peter Image Unavailable, Please Login
The operation of the crank sensors can only be tested on an ocilloscope. The timing sensors should produce a 1.5 volt spike, twice per revolution at cranking speed on a V8. The RPM sensor will produce a 1.5v sawblade looking pattern. But they can also be intermittant if there is a break in the windings. That can also cause a loss of function from engine temp. Coil opens when hot or vise versa. When doing continuity testing on them I remove them and whack them on a piece of wood while looking at the resistance reading. What symptom or symptoms are you looking to diagnose? Just reread your post. If you are reasonably sure it is an ignition thing remove the sensors and test them as I described. That will almost always reveal an intermittant sensor.
Intermittents are the nemesis of electronic repair technicians and unfortunately rarely fixed until they become full failures where the cause becomes in-your-face obvious. Probing is a waste your time unless you become lucky...my prayers for your good fortune.
