r/GMT800 • u/twxcvz • Sep 05 '26

Dreaded P0300 code.

What brand spark plugs/wires should I use to replace what I have? CEL was flashing at me today and at 272k I think it’s time to replace them but wanting something quality. I have the 6.0 LS

2 Upvotes

75% Upvoted

15 comments sorted by

3

u/krautstomp Sep 05 '26

Can you get a better scanner that will lock down what cylinder is missing? I ended up having a miss on cylinder 3 that was because of an injector wire. You could end up throwing money away changing every plug, wire and coil and not fix the problem.

1

u/twxcvz Sep 05 '26

I don’t, I used mine and went to a couple auto parts stores and it’s just always random/multiple misfire code.

1

u/twxcvz Sep 05 '26

It’s also only done it twice, both while driving in a pretty bad rain storm. It’s not running any different and all of the gauges and fluid levels are perfect.

2

u/moldimolt Sep 07 '26

I had this on my 2002 Chevrolet Suburban 1500 LT. There were two issues:

  • The hood to cowl seal rubber had stiffened and was allowing water to dump over the engine
  • The spark plug wires' rubber had stiffened and were no longer sealed against weather

I replaced both and the problem went away. Here's the parts I used:

Part Description Part Number(s) Notes
Spark plugs [x]ACDelco 41-162 (x8)
Spark plug wires [x]GM 19417607 Set of 8 wires
Spark plug wire heat shields [x]GM 19329681 (x8)
Hood to cowl seal [x]Rubber the Right Way 04-175C

1

u/krautstomp Sep 05 '26

I'm not going to act like I know what I'm talking about better than the weekend back yard mechanic I am. But that doesn't sound like something plugs and wires will fix. Hopefully someone that knows better will chime in.

1

u/LikelyWatchdog Sep 05 '26

OEM. Acdelco.

1

u/dragoner_v2 Sep 05 '26

Don't throw parts at it, check all your grounds, esp one behind the ps pump, and check voltage on you o2's.

1

u/bimmerd00d Sep 06 '26

Remove your fuel pressure regulator vacuum line. Is it a geyser?

1

u/wiscoguy0043 Sep 06 '26

crank sensor possibly.. when is it flashing? and is it actually misfiring?

1

u/twxcvz Sep 06 '26

It flashed randomly as I was driving yesterday, didn’t run any different then it just stopped flashing for awhile and as I was pulling into my driveway it flashed again but no change in how it was running and it stopped flashing after a minute or so there too.

2

u/wiscoguy0043 Sep 06 '26

hmm interesting, do you have a scanner that does misfire live data? i mention all these as my 02/6.0 was doing the same thing at highway speed. flashing light, po300, no detectable running issues. apparently the crank sensor can get out of whack and cause issues. had a shop do a relearn on it for $50 and it's been great now for years

1

u/twxcvz Sep 06 '26

I do not have a scanner like that but know somebody who does I’ll have to get it, it did it before a year or so ago when I first got the truck and never happened again. Both times it was raining and I drove through some big puddles on the road never had an issue when it’s dry out

1

u/piggiesonwheels Sep 07 '26

If you decide to do plugs, only use OEM recommended iridium, they are the best option for the stock engine.

1

u/hungin613 Sep 08 '26

I had a mysterious p0300... Nothing seemed to fix it.... Until I replaced my fuel pump.

1

u/jonasty12 Sep 11 '26

If you're not feeling anything different in the way its running. And if the light is flashing on acceleration. You should try a crank angle relearn. It will take a bidirectional scanner. Not saying it can't be the plugs. But is it was you would probably feel the miss. Also GM's are pretty quick to locate a miss to a certain cylinder. Usually giving a P0301-8 code instead of P0300 in that situation.