Hey guys,
Im in need of some help here if possible. I recently bought an 01 grand am with the LD9 engine. The owner had been driving it with a misfire for a few days. I limpped the car home and started looking into it. I replaced spark plugs, boots, and coil housing. Ater that, car runs like a champ. SES light went off but after about 100 miles, the light came back with codes P0300 and P0420. Car does not feel like it has a misfire. Im sure I would have noticed it.

I've been checking online but havent been successful at finding the right answer. Some suggest checkign fuel presure, coils, crank and camshaft sensors. Others point towards the FPR. Looks like they had just replaced the FPr though and once again, car doesn seem to have a misfire. Code P0420 pertains to the Cat.

I was wondering if anyone has had this issue before with their LD9 and maybe they can point me towards a good route. In the meantime i will start checking the sensors to see if anything comes up.
Thanks in advance!!!


03 cav
5 speed sedan

First thing I ALWAYS do on the 2.4/Quad 4 is check the vacuum lines, especally the one going to the MAP sensor. They always seem to split and break.




Currently #4 in Ecotec Forced Induction horsepower ratings. 505.8 WHP 414WTQ!!!
Currently 3rd quickest Ecotec on the .org - 10.949 @ 131.50 MPH!!!