Hi all,

I'm new to the forum and I just bought a 78 GMC PU a K15 I believe with either a 350 or 400 sbc.

Anyway It seems to knock at idle once it warms up. I need to change the oil on it yet, it's pretty black and thin, I also know that the truck came from NM, lower altitude, and I don't know if the timing was readjusted.

So I was wondering a couple of things. Will an altitude change cause an idle knock? What about bad oil?

Any input would be greatly appreceated especially where I should set the timing.

Thanks for the help,

Jason