i have been battling this rattle nock noise under light load after highway driving warm. Sounds simular to an old metal can converter rattle when they fail.

what is baffling me is only happens warm. Power does seem slightly off when happens.

Question is has anyone experienced this on a AJ27 style down pipe converter?

note:Yeas all chains/guides and super charger coupler replaced

 

91 octane gas or higher?
Any codes?

 

A warm engine is more subsceptible to detonation than a cold engine.

The XJR uses two fuel pumps. The second fuel pump only cuts in to prime the fuel rail at key position one, and to add fuel above 3500 rpm. Detonation is one sign that this pump may be on the way out. Especially if it happens at light throttle going up a mild grade.

According to the X350 technical manual, when the knock sensors detect knock, timing is not pulled as commonly believed. Instead, fueling is increased by the ECM. But, if the fuel pump is weak/dead, such an attempt is futile. I suspect the X308 follows the same management strategy.

You can check your pumps by directly jumpering power to the relay socket terminal with the key off. You should hear a quiet whir from the tank when you do this. No whir=dead pump or bad wiring beyond the socket terminal. Gurgling means the outlet hose at the pump may have popped off.

 

93 octane..no codes...fuel pressure good

 

 

Don't know what to tell you other than an experience I had recently. I had a small coolant hose go south and Im sure it flooded the valley of the engine. Until it dried out I had the same as what you had. So maybe you just need new sensors? I know once I remove my supercharger to change the hoses underneath, I putting in new sensors for good measure.

I have come to the understanding too, that the latter model 4.2 are much less expensive, are a direct fit other than the wiring being a little longer.

Chris