2003, S-Type 3.0 5 speed manual transmission 90000 miles
The car developed an octane knock and set a knock sensor code P0328 [ sensor on the right side above the starter]. I changed both knock sensors and now I have no Octane knock; but P0328 is back along with restricted performance message. Car will not rev above 3000rpm while driving. What should my next step be? Thanks

 

It should not rev above 3000 if parked - to protect engine & gearbox.

 

I should have added will not rev above 3000rpm while driving

 

Maybe if it can't trust the knock sensor it dare not risk destroying the engine.

 

Good point. Both knock sensors are new. Perhaps I have a harness problem

 

Best to start with knowing available voltage as many electrical faults or gremlins are caused by low available voltage.

Use a voltmeter to read voltage across the battery terminals after the ignition has been in the OFF position for at least thirty minutes. There should be a minimum of 12.6 volts available; if not, charge the battery for five hours at 2 to 5 amps and retest.

 

on v8s you can just plug in new sensors and see if your dtc goes away idk if the v6 has the harness accessible. knock sensors are ac voltage generators but they're checked for resistance to ground with a dc bias voltage

 

Both sensors are new. But it's possible I got a bad new one. I'm going to check battery voltage today, as suggested by NBcat

 

12.2 volts. Charger on will report back

 

I charged battery for 6 hours at 6amps. Well around 6 hours, when I went to remove the charger, it had shut down. I let the battery sit overnight and this am it was at 12.8V