What to test if 308 is running on 4 cylinders and how?

I don't know the resistance values of the sensors offhand, but they are listed in the owners manual under the electrical schematic section for the igntion system. Re: where to start to dx this problem, I'd first try the coil wires--ie switching them to see if the problem moves to the other bank ( actually move the entire wire from each coil and distributer and install on the opposite banks). Also check all of the electrical connections running from the Digiplex units to the engine.

 

You can't just criss-cross the coil wires--that would cause major problems! One way to test if it's the coil wire is to disconnect each coil wire from both its respective coil and distributer. Then, install the wire which was on the front coil/dist onto the rear coil/distrib and visa versa. If the bank failure then changes , after you switched the wires, then you know it's a bad coil wire problem. If the bank failure doesn't change after you switched the coil wires, then it has to be another component--such as the flywheel sensor, digiplex, or the wiring. I'm not an expert at testing the other components, but resistences can be checked by way of an ohm meter , connections can be cleaned and tested, etc. I'd call a dealer/ Ferrari mechanic re: testing the digiplex.

 

I believe that the coils can also be tested w an ohmmeter. I'm sure some of the experts on board to provide the specifics. Unfortunately, I'm not one of them! By the way, I have an '85 308 and this happened to me a year ago. It was a flywheel sensor and a case of old wires. A dealer dx'd the flywheel sensor problem.

 

There have been several threads on this in the past 3 years or so. One of them had sensor resistances, another had at least some of the pins for the diagnostic connector identified.

Try searching the old Tech Q&A archives for 'diagnostic socket' 'diagnostic connector' 'sensor' 'resistance'...

 

308GTS...the problem you are writing about has been the single most frustrating issue with my 84-QV. Living down in Florida has only made it more agrivating. I've found that I have to routinely check all of my connections to the coils for corrosion. If I keep those very clean and tight, she runs like a champ.

About two months ago, I replaced EVERYTHING including coils, distributor caps & rotors, wires, spark plugs...everything.

 

You can check the digiplexes by trying them one at a time. Figure out which bank is working (the tach is connected to the 1-4 digilex, so if the tach is working, 1-4 is firing. The boxes are located under a plate on the driver's side of the luggage compartment. Simply pull out the connectors and move them to the other box. If both boxes fire the working bank then you know it's not the digiplex.

The coils can be switched to check them, but it is necessary to switch ALL the wires attached to them, so you pretty much have to take them out and switch positions. Make notes on which color wires are connected to each terminal first.

If these checks don't work, it gets harder unfortunately to check sensors, wires, etc.

Dave

 

OK, did the search myself.
TDC sensors should measure 800 to 1.2K Ohms.

Most common failure will be opening up, not being way off on resistance. Other common failure would be shorted turns which usually aren't detectable with an Ohmmeter.