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I've got a buddy with a '99 K1500 RCSB 4.3 V6, it's stone stock and has about 150,000 on it. It is misfiring under load, especially climbing hills. It flashes the SES light and throws a code when it does this stating "Random / Multiple Misfires". We replaced the cap and rotor today and it didn't help. He put new e3 plugs in it about six months ago trying to fix the problem. I'm out of ideas any help would be appreciated.
:thanks: in advance.
Vacuum leaks, o2 sensors are the most common problems I've run into.
why not put some orignal a/c plugs back in it, since its all stock
i had the same problem and it ended up being a plugged cat.
run a compression test.if it is stock i would put ac plugs in it.ck for vacuum leaks.put a good set of plug wires on it
+1 on the plug wires..sounds like secondary ignition problem
Thanks for all the input we will start trying what you guys have said. I was thinking plug wires too but didnt want to just keep throwing parts at the thing.
Could have had a bad plug originally, then when he installed the new plugs, he could have cracked one, it's very easy to do and sometimes you won't even notice it. it won't hurt to check them again.
that many miles, original plug wires?
Get it on a scanner and see which cylinders are misfiring or if all of them. That will greatly narrow down the problems it could be.
Definately sounds like a plugged cat. Put it in drive step on the brake and rev it up without spinning the tires. Open the door and point your ear towards the ground underneath the truck. You should be able to differentiate the misfire sound between an engine issue or it being choked up with exhaust. If he has never put cats on it look no further. ASE Certified here.
Plug wires are original. It is misfiring on all cylinders pulling the code P300. I would assume that means plugged cats then because it isn't happening to one cylinder in particular?
I would deff say start by looking at ur plug wires, we had a car in here yesterday throwing the samy code, multi misfire it had 2 bad plug wires, gave it a tune up good as new... just my 2 cents....
i have the same code coming from my 2001 6.0L, ive sprayed the wires and coils with water at night, didnt see anything, didnt change anything, it has the original cats on it, kinda hard to rod out with the factory bends in there, i am changing plugs and wires this weekend, see if that helps, if not, gotta get rid of the cats somehow.. any more suggestions? it doesnt miss any, runs great, just flashes the code multiple cylender misfire... thanks for the help guys!
mine had p0300 and 2,4,6,8 had mor than 1000 misfires on each.took the kitties out and now she screams.take your rear 02 sensors out and see if the amount of exhaust coming out of the bungs are the same.if one is plugged youll know.or an infrared temp gun on each cat.my drivers side cat(good) was 180ish and my passenger (bad) was 365 degress.
thanks ill take a temp gun to the cats and see if thats causing the codes,,
I got the eBay long tune headers. They came with a Y pipe and deleted the cats. 02 sensors bolted right up. She screams now!
Sorry for not getting back to this, I have been very busy. The truck has apparently fixed itself; it was still misfiring after we put the cap and rotor on and my buddy didn't want to throw any more time or money at it so he just left it. Well some time in the last two weeks it fixed itself. No more misfires, no more lack of power, it runs perfect. Time to sell it!