1996 chevy 4.3 PO420 code

Bustedknuckles · October 2, 2012

Ok so about a month ago Im driving down the freeway at around 65 and my engine starts to misfire, doesnt throw any codes just misfires. I was frustrated by this because id just changed the plugs and wires. Then after about a week of this it finally throws the PO420 code. So I replaced the cat, still misfires. Then I replace the injectors and regulator, still misfiring. Any ideas before i go and drop more money on shit i dont need??

W/T_Deluxe · October 3, 2012

Are you getting any other codes? With the misfire I would imagine its throwing P0300(If i remember right) random cylinder misfire. I know you said you had just changed the plugs and wires, but what type of plugs did you use? I know these vortechs pretty much need ac delco plugs. Also, when you did the plugs and wires did you do a cap and rotor? I've seen this cause alot of misfire problems on early vortech engines. If you do change it make sure you get a quality replacement. I've used autozone ones before and they would last about a week and then I'd have the same problem again. I've also seen (one time) a fuel pump cause this issue. We initially did most all of the above becuase fuel pressure showed good at idle and when we would increase rpm. However at highway speeds 45-65 we would get miss. Since the pump seemed to be whining anyway we swapped it out, and the missfire went away. That being said, before you do anything I would start small, change the fuel filter, check cap and rotor for exccesive carbon or moisture, and see where that gets you.

Bustedknuckles · October 4, 2012

All the plugs and wires were AC delco I put them on at the dealership. I was going to check the fuel pressure today but ill check the cap and rotor.

Bustedknuckles · October 4, 2012

Ok so i just checked the pressure and its idling between 53 to 55, and even giving it throttle it wont go above 59. I know this low, but is there anything else that could be causing this besides the fuel pump??

W/T_Deluxe · October 4, 2012

Yeah thats a little bit low, like to see above 60. When was the last time you changed the fuel filter? I was thinking maybe bad fuel too, but since you said you had this issue for over a week I doubt its just fuel. try changing the fuel filter. remember always start with the easiest and cheapest fix you can and work from there. I've seen plenty of people (myself included) blow hundreds of dollars chasing down a problem caused by a $2 part.