I put a rebuilt 350 in my car some months back and have had a problem with misfire at idle and serious oil consumption on #7 cylinder. So, now that I have no job , I have time to try to fix it. I reasoned that I had damaged the intake gasket at #7 while installing the Edelbrock performer manifold. Pulled off the manifold today and found no problem with the gasket. And there was no evidence of oil in any of the intake ports. The odd thing is that the #7 runner in the manifold is super clean, with the others on the lower plane being a bit less sooty than the upper runners. So, now I conclude that the #7 is burning oil because of some internal problem, but I am still left with an idle misfire and a mysteriously clean intake runner. What do you think is going on here?
Thanks in advance.

broken or upside down piston ring in #7, pull the head and look for a scored cylinder wall.
Hope i'm wrong; but ........... :(

How do you know it has high oil consumption on #7? Sounds like there's more story here.....


Check your valves, run a compression test, make sure the plug wires are landed right, make sure the rocker stud on 7 intake runner is tight in the head. Look if 7 intake has a valve seal. Leakdown test, intake manifold pressure test with all the intake rockers off, but you have the intake off. I have been known on way more than 1 occasion to silicone intake gaskets and re-use them if they aren't ripped to hell and gone. Lotsa things to check before yanking the head.

Compression is 160-170psi on all cylinders. The #7 plug is oil fouled to death in a couple of months and is soaking wet with oil when it is pulled out. The very clean intake runner is a puzzlement to me at this point. Whatever the real problem is I am not sure. But it initially behaved like a vacuum leak, requiring a rich idle mix to smooth out the engine. Closing off all vacuum ports did not help, so I suspected a damaged intake manifold gasket which would be consistent with high oil consumption. However, the gasket seemed just fine. Now it appears that there is a more serious problem that would require more teardown of the engine .