this really drives me nuts and i hope someone can help me with it,,

my 05 XJR started to rattle from engine bay,, i believe the engine itself rattles,, it rattles just like nuts in a jar,, the symptom can be described as the following:

• it rattles in partial throttle on higher gear especially under load
• rattles faster and louder as i press the gas pedal until engine sound takes over
• no rattle if revved in neutral
• all pulleys sounds ok
• all covers/plates may wiggle removed from engine bay
• revert back from MG CAI to stock air box
• spare plugs replaced
• coils checked ok
• engine oil changed
• rattle is completely independent from road surface and driving conditions
• car performance is noticeably reduced
• had a "restricted performance" twice and it went out immediately
• even poured a bottle of liqui moly fuel injector cleaner in a full tank

i tried almost everything,, and am not sure if that rattle is actually a knocking detonation or anything else,,


please,, help,,

 

Loose catalyst brick maybe ?

 

tried to hammer them as well,, no rattle at all,,

 

i used torque app to read codes and it pulled P1646
long term fuel trim up to 3%
timing adv up to 50deg

any idea?

 

HEATED OXYGEN SENSORS MONITOR DRIVE CYCLE
Upstream (Universal) oxygen sensors:

5. Idle engine for 11 minutes.
google code plenty of info around

 

switched upstream sensors and the code persists,,

am out of ideas,,
please,, help,,

 

Maybe A Knock Sensor if equipped.

 

is it possible that P1646 pops without a CEL?
if i didn't scan i wouldn't ever know about it,,

 

if a knock sensor went out it would throw a code,, right?

 

Sounds like detonation to me.

 

i totally agree,,
but still can't find a reason behind it,,
i checked short and long term fuel trims and they're perfect which eliminates fuel starvation and intake vacuum leak,, fuel pressure is always close to 60psi,,
could it be high IAT as i sometimes get a P2601 which relates to SC coolant pump? what is the normal operating IAT?

 

my guess is it is running excessively lean for some reason. You need a wideband O2 sensor.

 

i noticed that pinging is more likely as the ride goes longer,, no pinging in the first 15 minutes or so of riding after a cold start,,

 

i also found a TSB which instructs to reconfigure the ECM if a V8 SC engine exhibits knocking and pinging,, is that doable with SDD?