308qv tach signal

The brown wire from Pin 10 of the Ignition module goes to the Tach (-) as the tach signal. The ignition module uses the speed sensor for the information.


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If you are looking for a low voltage signal that has 1 pulse (or cycle) for each crankshaft revolution, I don't believe that sort of signal exists anywhere in your electrical system. Can you describe "my multimeter (reads rpm)" a little more? If your multimeter can also measure frequency (Hz or cycles/sec), and you know/count the number of teeth, N, on your flywheel ring gear (this thread, http://ferrarichat.com/forum/showthread.php?t=211033, indicates that N = 144 for a 308), and measure "Hz" between the two wires of the RPM flywheel sensor (measure between pin 2 and pin 3 at either ignition ECU, or at the intermediate connector, or at the RPM sensor connector), the result displayed on the multimeter can be translated into engine RPM:

Engine RPM (rev/min) = Multimeter reading from the RPM sensor (cycles/sec) x 60/N

 

OK, that specialty meter has circuitry built-in to do the math, but I don't follow this:

because your OM schematic shows that each of your coils should only have 2 low voltage wires attached - not 8?! One coil should have a yellow wire (+12V) attached to terminal 15 and a yellow/black wire attached to terminal 1. The other coil should have a yellow wire (+12V) attached to terminal 15 and a green wire attached to terminal 1. Do you have something completely different (or are you trying to measure at the ignition Digiplex ECUs)? Normally, for such a meter you would connect one lead from the meter to terminal 1 (on either coil) and the other lead from the meter to ground (or maybe terminal 15, if the instructions so indicated).

 

That's the right place (there are only two terminals on each coil even though they have multiple wires connected). What do your instructions say -- connect between terminal 1 (the green or yellow/black wires) and ground (the chassis or engine), or between terminal 1 and terminal 15 (the yellow wires)?

 

(Assuming that you've got the probes in the correct holes on the meter, and the meter selector switch on the 4 cyl RPM scale - not the 8 cyl scale) This means connect the red probe to terminal 1 (where the green or yellow/black wire is connected) on one of the coils (doesn't matter which one).

Touch the black probe to the (bare) engine cylinder head casting or a good ground point on the chassis.

If you still get no result, then something must be wrong with the meter. Have you confirmed that it works in other ways -- like measuring the voltage between the two battery terminals?

 

Don't worry -- confession is good for the soul, and anyone who says they never made a mistake is fibbing

Are you saying that it's off a fixed 150 RPM at all RPMs, or does the difference get greater at higher RPM? (In a strange coincidence, my tach also reads about 1150 when the engine is really at 1000 RPM -- but I didn't check it at higher RPM.)

 

I don't have a manual for the Euro QV but mine are under the rug in the boot quite near the left sidemarker light. But I question your mission at this point. If you are on the short end of the learning curve and don't have a problem with the engine, I respectively add that idle curiosity might work to your disadvantage here.

Readable wiring diagrams can be found, regardless of age.