P300 on vortec v6 why


Asked by Jul 27, 2014 at 02:17 PM about the 1997 GMC Sierra 1500 C1500 SL Extended Cab SB

Question type: General

I have a 1997 GMC 1500 with a 4.3 Vortec
v6 it has a p 300 random multiple cylinder
misfire code I have change distributor cap
rotor button and distributor and plugs and
wires cam sensor crank sensor and iCM
also did intake manifold gas.ket set
complete what else is causing it

6 Answers


Warped valve,check compression on all cylinder,s,one is leaking down,got same 4.3 in my silverado,went threw same as you ,replaced all,and found valve warped.


But it's only got 42000 on moter and it would only show one cylinder misfire if it was a valve correct


Not really,mine had 3 warped valve,s on different cylinder,s,being warped cause them to seat and sometime,s not,causing my random misfire on different cylinder,s.But that said check compression to rule me out.


How long did u let it set each cylinder to check the leak down


You will know within a few minute,s pressure want hold.



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