How to i get to my flywheel sensors to test?

flywheel is on the other side of the engine,

looking from behind, camcovers are right, flywheel/cluch is left
the srensors are just somewhat under the distributors

 

Your symptom does not really sound like crank sensors. A full on failure would be obvious and an intermittant failure is random often with a temperature element. When one fails on a 328 it will kill the motor, even if just momentarily. I have never seen a miss correctly attribted to one.

The only way to test an intermittant sensor is to remove it from the engine and gently tap it on a hard surface while reading the resistance value. You would be looking for a momentary change from 750 to zero ohms.

They are located on the adaptor plate that is sandwitched between the block and the bell housing. The plugs should be seen down below the oil filter around the removable cover plate above the timing marks.

 

Yes, even if briefly. The usual pattern is the motor gets hot and dies. Cools down and restarts. The sensor is a very light gauge winding. Temp changes cause the circut to go open but it will usually stay that way for a while. Like I said, in my experience anyway I have never seen one cause a miss.


I am not familiar with Magnecores but I have had aftermarket wires cause rough running. I had one that drove me nuts and in desperation changed the wires to OE. Problem went away. The Microplex ignition system is very sensitive to RF interference. The diagnostic plug is on the left bulkhead above the distributors and the cable runs from it down past 1-4 distributor to the box in the left side of the trunk. That cable acts as an antenna picking up interference from the wires and disrupts operation. We knew that from using the cable for the diagnostic box as a break out cable to service the cars. It would do the same thing when not connected to the box. The original Cavis and Taylor are the only brands I have seen that I know work and never cause problems and Taylor quit making the spiral core some time ago. Dave Helms bought the last of it and has quite a bit. Might give him a call.

 

Although not stock, this thread will show photos of sensor location on the flywheel. http://www.ferrarichat.com/forum/showthread.php?t=142242

The picture below from the OM is schematic of the sensors...that and the photos from the thread will make sense. Note wire pairs are red - black. Remove right tire and wheel well cover for access
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You have a 308. Losing either of the position sensors will kill only one bank. But even that will be a profound loss of power. It would be smooth though so still does not fit the description.

It is a little different than 328 in that sense.

 

Intermittant sensors are just not consistant. From the sounds of it your problem is pretty consistant.

If it can be shown or you really believe you have a condition effecting one bank I would be far more suspicious of a secondary ignition fault (between the coil and spark plugs) rather than a primary (from the key to the coils) fault.

You said you replaced 2 bad plug connectors. When they are just starting to cause trouble it is hard to see. Might consider springing for the other 6.

 

Maybe you should have replaced all the extenders. I've fixed two 308's exhibiting the exact problems you describe by just replacing all the extenders. They don't always show visible signs. Dielectric breakdown is a weird thing. I bet if two were bad (visibly), there's a good chance more of them are. YMMV.

 

That happened to me on 07.

These things will eventually harden and crack or whatever, given enough time

Keep a 308 long enough and you will be replacing these at some point

 

I would never argue with Brian on anything related to Ferraris, but I'll chime in on crank sensors.

I had an intermittent miss on our Mondial. Could not figure out what the hell it was, and it only did it now and then. One day I was driving around and another Ferrari buddy who was sitting in the passenger seat noticed that when the car did it, the tach went nuts. Strangely enough, I had never noticed that. I guess I never was looking at the tach when it happened. I looked at the schematic and noticed that the tach was driven from one of the ECUs, but had nothing to do with the other ECU. Looking at the schematic, it was also clear that if the tach was going nuts, it was getting that nutty signal from the ECU, well before the coil, so that ruled out the coils, wires and plugs. First thing I did after checking in here for advice was pull the connectors on the crank sensors and check them with an ohm meter. Two of them were about 600 ohms, and the third....the one connected to the ECU that drives the tach....was infinite. I had a flaky connection in the crank sensor that was "mostly" OK but every once in a while it opened up and the engine would go back and forth with misfires on one bank. $90 for a new crank sensor and never did it again.

So, my extensive experience (sample size of one) is that a flaky crank sensor can cause an irratic stumble. But mine only did it maybe once every 10 minutes for 2 seconds. If it had been on the ECU that drives the other bank (and therefore not the tach) it would have taken a lot longer to find!

Birdman

 

I agree with all of that but my big problem is his is so consistant. It happens with repeatability in a particular RPM range. That is hard for me to think is caused by a crank sensor. It is not something that is expensive to test but they really need to be removed to test well. On the 308 with 3 sensors one is not too easy to get out. The other 2 are not too bad.

 

It does sound like you are losing a bank at a specific temperature. You should get it warm so that it starts doing it, and then test each bank for spark. Once you figure out if you are losing spark on one bank, and which bank it is, you can start working backwards. If you are losing a bank, you can rule out fuel issues. If you are not losing a bank, it's possibly something related to the warm-up regulator. Several things in the K-jet system change with engine temp (warm up regulator, cold start injector, etc.). So it is important to know if it's fuel or ignition first. (Granted, it's most likely ignition).

If you are losing a bank, in theory, anything in the path of of the ignition circuit (crank sensors, ECUs, coils, distributors, wires, extenders) could do it, as things sometimes only flake out when they are hot. But I agree with Brian that it seems unlikely that the crank sensors are doing this with such consistency. Possible, but not likely. If they are, testing them cold will not help you. You will need to test them with the engine hot when they would be open circuit.

FYI, a crank sensor is just a coil of wire around a little magnet. It's like a little electric guitar pick-up. As the teeth go by on the flywheel, each one generates a tiny current in the sensor which goes to the ECU. So the only user-serviceable thing on the crank sensor is the connector which can get a little corroded. You can clean the connector. Nothing else on it can be "fixed".

Try torquing down the ECUs a little. They need proper ground to work. Check the ground wires on them.

These kind of problems are so annoying.

Birdman

 

FYI, if when this happens you can't really get the car over 4000 RPM, it is very likely you are losing a bank. In that case, do not drive the car unless you want to see it burn to the ground. When you lose a bank, the car is dumping raw fuel into the cylinders that are not firing, and subsequently into the exhaust and cat. On a single cat car, this is very very very very bad. On a dual cat car, it's only really bad. Either way its damn bad for the engine and the oil. As soon as you figure this out and get it fixed, change your oil. It will be contaminated with gasoline.

Birdman

 

Did you figure out the problem? Was it the extenders?