I need help

[Jmk6789]

I have a 98 Silverado 305 5.0

Just cruising along at 40, stopped at a light and when I pulled off the truck started running like dog ****, the only code it threw is P0300 random misfire code, it’s running super rich and it’s mainly misfiring at idle and when you take off and back firing a little when you hit the gas , also has hardly any power. I pulled the cap and rotor off and they both look fine and they’re only 2 months old. I pulled out all 8 plugs and the plugs from cylinders 2,4,6 & 8 are black and covered in fuel, the plugs from 1,3,5 & 7 are black but not as bad as the other fuel bank. Starting to think it’s the fuel pressure regulator under the plenum or an injector problem but definitely seems like it’s effecting fuel bank 2 the most. Please comment with any info you have, it would be greatly appreciated

 

[Biggershaft96]

If it ran good before and just started out of nowhere id throw another cap and rotor on it. It may seem redundant since you just replaced it but i had a hairline crack in mine once and the truck did exactly that, out of nowhere. Spent $150 having the chevy garage find that out, then another 75 to replace them. If theyre under warrenty it would ve a hood start. Report back with results.

 

[GarrettGmc]

Hey so I just had this problem the other week and was referred to this thread

http://www.gmt400.com/threads/454-v...fire-code-troubleshooting-and-solution.31561/

 

[Barry cowan]

Anone ever had any problems with a cylinder 6 misfire. I have already replaced spider injectors entire distributor plugs and wires I was getting bank 1 and 2 rich but they have went away ever since I got an ac Delco distributor cap. I can clear the code and it comes back in about 50 or so miles. It seems to run fine until the light comes on then you can feel the miss at idle I was thinking a stuck valve or something

 

[GarrettGmc]

I had misfire on number 6 and did the same thing plugs wire cap rotor and it came back, had a shop look into to and found my head was cracked and fouling it up, which prompted the rebuild. How did the plugs look when you reppaced them

 

[CoolDude1975]

I have a 98 Silverado 305 5.0

Just cruising along at 40, stopped at a light and when I pulled off the truck started running like dog ****, the only code it threw is P0300 random misfire code, it’s running super rich and it’s mainly misfiring at idle and when you take off and back firing a little when you hit the gas , also has hardly any power. I pulled the cap and rotor off and they both look fine and they’re only 2 months old. I pulled out all 8 plugs and the plugs from cylinders 2,4,6 & 8 are black and covered in fuel, the plugs from 1,3,5 & 7 are black but not as bad as the other fuel bank. Starting to think it’s the fuel pressure regulator under the plenum or an injector problem but definitely seems like it’s effecting fuel bank 2 the most. Please comment with any info you have, it would be greatly appreciated

Save yourself the hassle and just throw a full tune up on it, don't use **** parts either or else you're going to be redoing it.

 

[Barry cowan]

I had misfire on number 6 and did the same thing plugs wire cap rotor and it came back, had a shop look into to and found my head was cracked and fouling it up, which prompted the rebuild. How did the plugs look when you reppaced them

They kinda had a gassy film but the spider was messed up at the time replaced them a couple times all but number 6 looks good it has a little bit of gas filiming on the plug after about 40 miles or so. I've been wondering here lately if I got a bad spider unit it was an ac Delco from Amazon

 

[slowburb]

This sounds like a sealing problem, maybe valve, maybe head. Compression test and leakdown test are both in order.

 

[Barry cowan]

Thanks everyone for your time.
Update kinda been side tracked a lil got lucky and got it to pass nc inspection ended up pulling the plenum again and kinda moving the new spider fuel lines thinking maybe the number 6 injector tube was restricted a lil. Ended up getting a new upper plenum gasket kit. The truck ran Better after I tested it I drove it about 40 miles on the highway had a high idle come back still thinking that's a small vaccum leak somewhere. I know how to do a compression test when it comes to leak down what should I do wait a minute and see how the cylinder psi holds up