83 308 help

Mondial QV:

JOFA socket for electronic ignition module diagnosis pins 3 & 4; pins 5 & 6: are the pin pairs for the flywheel sensors.

If you are asking about the terminals on the electronic ignition modules:

Terminals 1 & 5 are the sensor terminals on both individual electronic ignition modules. Terminal 4 in the module connector does not have a wire going to it, so start counting the terminals from that end of the connector to find terminals 1 and 5.

Test:

Not cranking - key off: the sensor resistance should be 750+/- ohms.

The cranking sensor voltage should be .5volt to 1 volt, hopefully.

The tach sensor does not have JOFA test pins.

You can also check the sensor ohms and sensor voltage with a multimeter at the respective sensor connectors by removing the left rear wheel and inner fender panel to get to the sensor connectors, and the electronic ignition modules, also.

You can also check the tach sensor at the sensor connector if you remove the inner fender panel. It is the easiest sensor to change.

Most experts (I'm not) say a bad tach sensor will cause both electronic ignition modules to quit at the same time. I have never checked to see if that is true.

In some ways it is easier to remove the fender panel than trying to get a meter on the right pins in the JOFA diagnostic socket.

The only way you can tell for sure which electronic ignition module is which is by tracing the sensor wires to the respective module. Someone may have switched them at some time, which really doesn't make a difference to the spark plugs. That sounds a bit unusual, but the modules are wired that way.

Do you have 12volt + at the coil terminals when the key is turned on?

You can also run a (long) jumper wire (10 or 12 gauge) directly from the positive side of the battery to the yellow wire on either coil to make sure you have 12 volts at the coils in order for the motor to run.

You can also connect a voltmeter from the yellow wire on the coil (and the other voltmeter wire to ground) while you crank the motor to make sure you are not dropping a significant about of voltage to the coil while the starter is engaged.

Sometimes the Ferrari ignition switch (at the key) starter circuit will reduce/drop the voltage so much the electronic ignition module can not function properly. If your ignition system at the coil drops below 10 volts +/-, while you are trying to start the motor, you could have a voltage drop problem in the switch circuit. This may require a helper to turn the key while you check the voltage at the coil while the starter is engaged. Removal of the switch to clean the contacts is already in another thread.

It is somewhat unlikely that both flywheel sensors and both electronic ignition modules would go bad at the same time.

Good luck,

Jerry
DRG

 

You seem to be measuring the wrong thing here -- the resistance measurement is a static test with the respective RPM or TDC sensor unplugged (and not while cranking the starter motor). It's sort of a one-way test -- i.e., 0 Ohms or infinite Ohms confirms a bad sensor that needs to be replaced, but getting the "good" value of ~700 Ohm doesn't necessarily mean that the sensor works.

For the operational testing with the starter motor cranking, you need to measure the AC voltage between the two terminals of each sensor while it is still plugged in (this can be tricky because getting access to the wires when plugged in isn't easy, but, if you have the diagnostic socket, they can be accessed there as Jerry mentioned).

For the RPM sensor = something like 2V AC minimum with the starter motor cranking

For the TDC sensors = something like 0.2V AC minimum with the starter motor cranking

See this thread for more description (even though it's for a 3.2 which only has one TDC sensor, the RPM and TDC sensors are the same as on your QV):

http://www.ferrarichat.com/forum/technical-q/149281-3-2-mondial-ignition-problems.html

Searching on "voltage RPM TDC" might get some other threads too.

 

Your owner's manual has a good quality wiring diagram in the back of it. If you don't have the manual, here is a link to a pdf copy you can download / print for the MY83 QV --- it is US spec, but the systems you are interested in are the same for all the versions. Diagram is on the last few pages of the manual.

http://www.ferraridatabase.com/The_Downloads/The%20Documents/Owners%20Manual%20308%20QV%201983%20US.pdf

 

Put an ohm meter on the crank sensor terminals. Should read about 7ohms. 0FL means open circuit= dead sensor.

You could also have sombody crank the engine, while you check the ohm readings to see if it drops out.

 

The pins I referred to are the connector pins in the JOFA ignition diagnostic socket.

I do not know whether a 1983 308 GTS actually has the diagnostic socket. I have never worked on an 1983 308 GTS, so I can not say for sure if your car has one.

On my 1985 Mondial QV it is located in front(toward the front of the car) of the intake plenum a little to the left side of the motor. The socket faces up and has a rubber snap in cover.

A "JOFA" socket is the name of the test equipment "JOFA" used to plug into the diagnostic socket. The pins in the JOFA socket are numbered on the ignition component and wiring schematic in the Factory Workshop Manual for a Mondial QV. They are also numbered on the factory wiring diagram.

If you do not have a JOFA socket, it is not a problem. You can, and probably should, check the sensors at their respective wire connector leads, anyway.

Regarding the flywheel and tach sensors. They are identical by function and part number, although they serve a different purpose in the ignition system.

If I remember correctly the flywheel sensors are located at approximately 7 o'clock and 10 o'clock, the tach sensor is located at approximately 2 o'clock, all mounted on the outer area of clutch bell housing near the motor. Typically, the factory sensors have two wires in a black plastic cover about 18" long, with a two wire connector near the electronic ignition modules.

To test the sensors I mount them in a lathe tool holder and position the sensor so that the lathe chuck jaws passes within 1/32 of the sensor when the lathe chuck is spinning as fast a my lathe will run. I have never checked the RPM of the chuck when I do this, but it is probably over 500 RPM.

The sensors, with the respective volt meter leads connected individually to the two sensor leads, will produce about 1 volt at that RPM when the sensor is mounted on my lathe, but will produce substantially more at higher RPMs, as when your motor is running. I have seen as high as 9 volts when live testing in the car. This is for both the flywheel and tach sensors.

I think the static resistance test is best conducted when the sensor is disconnected from the electronic ignition module. (as Steve stated) I do not know how the sensor circuit in the electronic ignition module would affect the sensor resistance if it was connected to the module at the time you checked the resistance, but I wouldn't do it.

If the sensor has zero ohms (no resistance) or infinity ohms (open circuit - wires are not connected to each other inside the sensor), it is not going to work properly.

Regarding the 12volts at the coil leads. The voltage can be substantially different when the starter motor is engaged, as compared to checking the coil voltage only with the key in the on/run position.

A substantial voltage drop at the coils while the starter is engaged is very possible, and can be enough voltage drop to keep the coils (step up transformers) from producing sufficiently high voltage to the plugs for the plugs to spark properly.

If you know how to check the plug spark while turning the motor over in the key start position, a small red inaudible spark is insufficient, you need a strong blue spark that you can actually hear (snap), for the motor to start and run properly.

The sensors are actually Hall effect devices. You can look up "Hall effect" sensors on wikipedia and other places on the internet, and it will explain how they work, A real neat scientific phenomena with a real life application. I love it.

I have used the same type "Hall effect" sensors to signal (ie: count) wheel revolutions for a very precision speedometer on a time/speed rally car. A Hall effect sensor is indispensable if you want to count or signal revolutions on any rotating part.

If you read all of this - you are at least persistent.

Good luck,
Jerry
DRG

 

See photo in post #2 here:

http://www.ferrarichat.com/forum/308-328/143953-flywheel-pickups.html

 

Did you have your meter on DC Voltage or AC Voltage?

 

Just to be picky... these are not hall effect sensors. Hall effect sensors need a constant voltage supply and ground so would have 3 wires. These are simply coils wound on a magnet.

 

Yes, you are on the right path for those results.

There are so few transitions in the TDC sensor signal that it's a fairly, low AC voltage component during cranking so I'm just interested in gathering more information about people's experience making this measurement and the result -- I can not accept "0 volts" as a real result (so TIA for offering to remeasure).

 

Awesome! I sent you a pm
Thanks
KEVIN

 

Check both your tach sensors (old one and new one) for physical damage / contact marks on the tip. It is rare, but you may have something stuck in the teeth (or a partially broken and "flagging" tooth) of the flywheel that it is making contact with, and damaging, the sensor.

Other than that, check your wire harness and connections for that sensor ---- all the way back to the ignition module (Digiplex). Other than that, it may be the Digiplex (one or both) itself that is bad.

 

Will the car start if one digiplex has gone bad?

 

If there is a good tach signal being supplied, yes, it will start and will even run ---- but only on the one bank that is connected to the working Digiplex. Without a tach signal, the car may start (poorly) but will not run even if both Digiplexes are good.

Many, including myself, have had the experience of limping our cars home after a crank (TDC) sensor for one of the banks has failed ---- which effectively shuts down the corresponding bank as if one of the Digiplexes was not working at all.

The setup of these V8's is essentially that of two, fully independent, 4-cylinder engines running in tandem (tied together only by the crankshaft). So, it will run on either of the 4-cylinder banks only ----- albeit with 1/2 the power and dumping a bunch of raw gas (as the CIS system will keep spraying fuel into the cylinders even if the ignition system is not operating) into the header and some into the oil sump, too .

 

this ...
especially the plastic connector (C36) on the frame in front of the expansion tank near the left rear shock - they can be pretty worn
and that`s where the sensor wires are distributed to the digiplexes

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