99' gmc sierra, 4.3l v6. p1345 code, surging/misfiring under light load

[zahlon]

Hello all, This is my first time posting here.. id like to start by saying im fairly mechanically inclined, but i figured i should reach out for help before i started throwing parts at my issue..

I just purchased the 99 sierra. Im actually quite well versed with the 4.3l engine. the truck has CEL light on, and idles rough when cold, and has random misfire under light load. even if its in park. seems to clear up above 2k rpm.

On the way home i stopped and had the Code read, and i got a P1345 (crank or cam sensor) and a p0300. (random Misfire). Im going to assume the 2 are related but, thats as far as ill go for now.

I guess my question is where should i start investigating, My guess would be the timing chain could have skipped a tooth, which correct me if im wrong, would exibit the same symtoms im currently dealing with, and do to the fact the truck has 280k miles... seems like a decent guess..

any ideas? would love to hear from people smarter than me..

cheers
Nick

[Blue Bowtie]

Welcome Aboard!

What? Chain stretch at only a quarter million miles?

Yes, that seems plausible.

As you know, the CMP is part of the distributor. A stretched and skipped chain will affect the CMP/CKP relationship, the cam/valve timing, the balance shaft timing, and may cause spark scatter due to less than optimal rotor position. Your analysis seems reasonable.

You could attempt to reset the CMP timing by rotating the distributor head. This could resolve the timing and DTC issue, but may not resolve the idle and random misfire problems due to the possibly late valve and balance shaft timing.