Hi all, relatively new to the forum. The girlfriend recently picked up a 98 Grand Prix GT (White, Two door, N/A 3.8). We bought this car off of my boss, who had the car for about a year. Anyways, the car has had the motor replaced about three times. I knew about this before the car was purchased. I believe that there is something simple going on to cause this; spark knock, fuel deprivation, lubrication deprivation, or just plain coincidence.
From what I know the reason the last motor was replaced was due to a rough knock at idle. The current motor has what I would describe as a "rattle" more like piston slap. This seems to only occur under load, when the throttle is snapped open, or shut quickly, or if you float the throttle open and closed slightly around 2,500rpm. What I'm asking for is input based on this information as to what kind of common problems could possibly be taking out a N/A 3.8.
Scanning with my Solus Pro shows me only a p0400 evap emissions code - no misfire codes, and no air metering codes. I see STFT at 100, and LTFT floats between 128-130 which I read on this forum to be about where it belongs. I don't believe the cat to be plugged up because the car still gets great fuel economy and does not lack power. Although the fuel trims are within range, the O2 B1S1 seems to read lean more often than rich - but seems to be reading properly. It does not have a dead miss, all the injectors are pulsing, pulse width seems to stay around 3.4-3.8ms at idle in park.
The car is up at my shop, so I'm planning on trying to check fuel pressure, fuel delivery volume, and change the filter. I'm going to clean the MAF sensor although it was reading properly, as well as smoke test the intake for vacuum leaks.
Any advice is greatly appreciated!
