308 QV failed emmissions bad

It does seem rather odd to ever measure + or - 12V on the O2 sensor output wire -- I'll have a peek at the schematic to see if I can pick up a clue/reason, and you could always try unplugging the O2 sensor heater (after the device is already fully-warmed up it should stay hot enough for at least a few moments). But can you clarify -- was the O2 sensor output wire plugged-in or not plugged-in when you made those voltage measurements? At your reported super-rich level of 9% CO, I would've guessed, when unplugged, the O2 output wire would be pegged up at the +1V level, but plugged-in to the injection ECU anything's probably possible (e.g., if there's a fault with the injection ECU itself).

 

The O2 sensor protection relay is on that same electronics plate in the rear trunk (although a better name would be "the relay for powering the injection ECU that has a fuse and Zener diode inside that protects the injection ECU from an alternator over-voltage condition" -- you can see why they shortened the name ) -- see Fig 91, page 102, in the 307/84 OM -- relay C with the fuse. I believe the terminal with the P (beige) wire should be +12V relative to chassis ground all the time, and the terminal with the three PN (beige/black) wires should also be +12V relative to ground when the engine is running (i.e., when relay C is closed, the terminal with the P wire is connected to the terminal with the PN wires) -- this is the +12V power source to run the injection ECU system (but the schematic scan in the 307/84 OM from the Owners Site is really crappy, and I think they mucked up the internal starter motor/solenoid wiring -- i.e., the P wire should be connected directly to the +12V battery cable).

Can you confirm that your O2 sensor has only 3 wires? The schematic shows 4 wires because it shows separate grounds for the sensor element and the heater. Anyway, my thought (if it is a 3-wire device) was to measure the voltage between the common ground N (black) wire at the O2 sensor (with everything plugged-in) and the engine block (or another suitable chassis ground) -- if it reads more than a few tenths of a volt when the engine is running that would indicate that you have ground problem in the big ground node shown between items 124 and 81 on the schematic -- just a thought on something else to check...

I still can't understand how unplugging the connector from an already "open" safety switch would make any difference unless the terminal on the safety switch that hooks to the N (black) wire is also connected to ground thru the body of the safety switch. With:

key "off",
safety switch unplugged,
air flow plate deflected,

if you make a resistance measurement from the terminal on the safety switch that is normally connected to the N (black) wire to the engine block or cyl heads is it zero ohms or infinite ohms?

 

Well, that might explain the unplugged vs plugged-in difference you're seeing. The FD would be at ground via the safety switch body IF the N (black) wire was connecting to a good ground. Did you try measuring the resistance from the unplugged N wire to ground (or from the FD body to ground when the safety switch is plugged in and the airflow plate deflected downward)? Actually, it would be better if you could measure the voltage from the N wire on the safety switch to ground when plugged in and the engine running -- if it's not very close to 0V that would confirm that you have a problem in that big common ground node.

Keep chewing, my guess is your system had/has an electrical fault and then someone added a 2nd fault by trying to tweak the A/F mixture screw .

 

This protection relay was the problem with my frequency valve not buzzing. When the FV would not buzz, the car would run rich and barely rev up. When I wiggled the connector at the protection relay the FV would start buzzing and the car would run fine, until it was parked, and the next time it would mess up again. I thought it was the connection at the relay, so I removed the connectors one at a time and soldered them, didn't fix the problem. It turned out to be the points in the relay not closing electrically, I tried the "electrical wonder cleaners", no help, so finally I had to refinish the contact points with fine sandpaper. Once I did this I have not had another problem.
My car (May 84) had the earlier protection relay without the fuse. It had a fusable link inside, which I changed to a replacable external type. Hope this is of some help.

 

Nice work in tracking this one down Larry. I also had to replace the same (ECU 12V power relay) on my '88 3.2. My relay had the external blade-type 10a fuse. Incidentally, that relay is actually a porsche 928 part and I was able to get it online for about $85 rather than the $200+ Ferrari charges for the identical part. The cause of the failure on my car was a disconnected aerial drain tube which allowed the ECU trunk well to literally fill up like a swimming pool. Tough for everything to work properly while submerged....

 

Have you priced either one recently? Prices and availability have changed.

Many promised the 928 part but when I said I'll take one the closest I got was 8 weeks from the Fatherland for an undisclosed amount.

Ferrari price is over $500 and you can have it today.

 

Not so Rifledriver:

Prices have not changed. Go to www.928gt.com. In stock for $94.83 and available to ship today. Part No. 92861512400.