P0300 on 1997 Silverado 4X4

My 97 silverado with a 350 was running fine when I left to go to the store. I walked out of the store and when I started it, it was missing and driving home, had no power. I got home and hooked it up to my scanner and a code P0300 along with a P0157 came up. I have recently replaced the intake gasket, new distributor which came with the cam sensor, cap. rotor button, plugs, and wires. According to the research I had done off this website, the only other possibilities included the coil and possibly burnt valve. I wasnt sure but if it was a burnt valve, then it should be the cylinder that has the burnt valve thats misfiring instead of multiple. If anyone knows if I'm correct in that idea, please let me know. Otherwise I was leaning to the coil. I am aware that I may have a bad O2 sensor but I had never seen one that would cause a problem this severe. Im almost sure that when my intake gasket blew awhile back, thats the reason why the O2 sensor was wiped out. Any help with this would greatly be appreciated.

Check timing...the distributor may be out a tooth or so.

Good luck and keep us posted.

Check fuel pressure and flow

I have checked timing and it was right on. Altho I havent checked fuel pressure yet. EGR valve was fine. I also noticed alot of oil smoke coming from under the vehicle that had never happened before. Was wondering about the converter. Just doesnt make sense it happened all at once with no warning signs. Ill check fuel pressure and get back.

I have similar symptoms with my 2003 Silverado 2500 HD 6.0 with 89,000 miles. It returned the P0300, random misfire code. It started to flash the code during 55-60 mph. It recently started to get worse and happens above 35. Temperature outside or of the engine does not matter. The interesting thing, on another thread a user mentioned, his battery died around the same time. Mine also died around the same time. I have short somewhere, since I measured .5 mill amps draining somewhere. Fuses are ok, I was more focused on the misfire, maybe I will focus on the short. I have replaced the plugs and wires with ACDelco. Note, I replaced the plugs 1 year before this started to misfire, during my regular maintenance.
Last night, I replaced the intake gasket per an ALL DATA service bulletin. Referring to the original ‘orange’ gaskets have had issues, and to replace with the newer ‘green’ gaskets. This would make sense for misfires if there would be an air leak. Sure enough same issue, however, it only misfires again at 55-60, like it got ‘a little’ better. The fuel pressure is good and holding (60psi), fuel pressure value works. The O2 sensors seem to fine, the numbers are not off. I am unable to graph the curves, so it is hard to be certain. It starts immediately when you turn the keys, so I doubt it is the coil. I guess my next step will be to locate the short, maybe take some of the plugs out (inspect) and re-seat all the plugs. I will also try running the engine in the dark and see if I see sparks. Each plug has its own module.

Thanks,
Sebastian

I replaced the fuel filter, still no good. There is a little bit of a flutter out of the drivers side exhaust. So I decided to pull the plugs and inspect them. I found them all in good shape other than the cylinder 3 plug was wet with gas. I then decided to check the compression maybe thinking I had a burned valve. I checked both #1 and #3 cylinder so far and and had approx. 135-150psi out of both. I couldnt go any further due to the weather so Ill check the rest tomorrow. At this point Im aggrevated but its not something I can walk away from and go back to, this is my only mode of transportation at this point. I cant help but think that its really something simple but its just not hitting me yet. I had an O2 sensor code before after the intake gasket went bad which was for bank 2 sensor 2 but it went away, after I cleared the code yesterday I had a P0135 which is an O2 sensor code for bank one sensor 2. I was thinking maybe it was the O2 sensor but now since I got a different code, I'm not so sure. I had to send my PCM to Hypertech and they checked it and reflashed it and said it was fine so Im ruling that out. After I get the compression test done on the remaining cylinders, I should be close to narrowing it down.

thanx

Ok I feel stupid now. I went to check spark on all the cylinders. #3 and #7 were both really weak spark. So, I took the cap off and looked under it and there were no signs of arcing anywhere. Then it hit me, the cap had plug wires 3 and 7 side by side. So I went and found my old cap that for some reason I had kept around, put it on the truck and guess what, problem solved. It was the cap the whole time. Kinda aggrevating when you put all that effot and it turns out to be something simple right in front of your face. Thanx to everyone that put their thoughts in and tried to help me. It was all appreciated.