Had the engine die on my tonight after some "spirited" driving.

I suspected plugged cats a while back because I was getting a foul smell, poor gasmileage, and it would die pretty much every time I would get on the throttle hard and clutch in, or if I came off of cruise control and clutched in. I then replaced the factory cats with Berks HFC, and new rear O2 sensors. Mileage has been a little better, but I still have a slight foul smell, and it has died twice on me in the past couple months since the swap.

Tonight I was out on some back roads, not running the car hard by any means, but I left it in 4th and/or 5th depending on the road and running around 70mph for a little bit of pull out of corners. Got onto a main highway and drove nice at 65ish mph in 6th for about 5miles, clutched in to turn onto another road and the engine died once the R's dropped.

I have a Stillen SRI, and I cleaned/re-oiled the filter about 2500 miles ago. Replaced the plugs about 7-10k miles ago. Fresh oil a couple weeks ago. Nissan did a diag check and re-learn last Nov.

What things should I be looking into?

 

Guy here at work had the same problem with his Titan. I don't know if the G35 has them, but it was the Pre-Cats that got him. Ended up having to get a new engine. Destroyed the rings and valves.

 

the pre-cat O2 sensors?

 

On most cars they have on the headers what are called pre-catalytic converters. They are essentially small catalytic converters used to further reduce emissions. Like I said, I'm not sure the g35 even has them but until you find out STOP DRIVING THE CAR. If you haven't damaged the rings or valves yet, you WILL.

The added back pressure can destroy your valve seals and rings. If the rings go it'll take the piston walls with it and probably the rods with a very slight possibility of damaging the crank. That's what happened to my co-worker, and it was just cheaper to buy a used motor than it was to rebuild the old one.

Take all of this with a grain of salt. I'm making a best guess from your assumption of clogged cats. Based on your description it wouldn't surprise me if that's the case, and it would't surprise me if your rings, valves, or both are damaged. I know Nissan had a problem with that for a while.

Or it could just be an electrical glitch with a spark plug not firing right. Interweb diagnosis isn't notoriously reliable

 

Ah yes I know what you are talking about now. I'm gonna say no on the pre-cats. I dont remember seeing anything when working on it, and they dont look to have them in stock photos online.

I know there was an issue with bad sealing rings in some motors and oil consumption issues, but I've checked mine and it doesnt have the symptoms.

I'm going to change the plugs again, maybe one is faulty. But something tells me its more than simple plugs.