My z31 is still doing this bogging out thing. When I get on it, it revs fine to about 4000 and from there it just boggs out for the rest of the gear. I don't know if this is a fuel problem or a timing problem. I replaced the fuel pump and put in a better flowing z32 filter. I had a timing light up to it the other day and it was just fine. But there is one thing, my dash says the o2 sensor is bad. I haven't replaced that yet but could an o2 cause a car to bogg out like mine does? I also pulled out some of the plugs and they had white tips on the electrodes. Does that mean that the car is running lean? I'm buying an air/fuel guage in a coulpe of days so im hoping that it will tell me what my car's doing. But any help would be great.