If you run 93 octane gas in a 10 to 1 1989 928s4 will it matter if the sensor(s) are bad? My car got 160k on the clock and by the look of the sensor wires they look like they could be factory installed. No cracks in the wires just that been there for years look. While I can pull the intake to replace them it would be much easier just to always add Hi octane gas. Would that work?

 

The knock sensors being bad causes the ignition to retard automatically to protect the engine - you can still drive the car, but it'll be down on power regardless. From memory its 3 degrees for a knock sensor fault (6 degrees for hall sender)

One of mine (front) showed up bad as a fault code when I plugged in a JDS Spanner (aftermarket equivalent to Bosch Hammer) - so I replaced both whilst in there.

 

May as way change that too. Looks like that intake is coming off. Only way to get the car to give 100 percent of what it has is to replace all the sensors and injectors.

 

If you do a search on here, using "inlet refresh" or similar you will see lots of advice on what is worth renewing while you have the inlet off. A typical list will mention knock sensors (not expensive), ISV, ISV hoses, throttle switch. The big vendors 928 Specialists, 928sRus, 928 International have inlet refresh kits, or will advise.

With a faulty knock sensor the EZK will automatically retard the ingtion by 6 degrees to prevent engine damage. Raising the octane is a waste of money. Spend the money on replacing the sensors.

 

Do the intake R&R - I just got mine back from the shop yesterday, and it is a truly wonderful improvement!

New gaskets, new ISV, new TPS, and new knock sensors. It's a long job (or an expensive one) so do it all while you are in there.

 

There's perhaps a 928 owner close by who may own a 'hammer' and can diagnose the knock sensors, hall etc etc.

The intake R&R is not that hard to do for DIY; just takes time and money.