Rough idle on fresh rebuild, 4.3 Vortec

[bubba68ss]

Picked up a ZR2 Blazer with a rod knock, put my rebuilt 4.3 from my truck in it, got it running but it's a bit shaky at idle.

Here are the symptoms;

- bank 1 has sooty plugs while bank 2 has normal clean plugs
- LTFT on bank one is reading 25 while bank 2 is about 4 (normal)
- Idle rough (shaky) but drives
- engine smooths out and runs nice as RPM's rise but lacks a little power.

This is a fresh rebuild and I can't find any vacuum leaks. If it were a vacuum leak, wouldn't both banks be getting too much air since they feed off the same intake?

Am I looking at a bad O2 sensor which is telling the PCM that bank 1 is lean and it is dumping lots of extra fuel trying to compensate? O2 on bank 1 is reading low numbers while the O2 on bank 2 reads throughout it's normal range.

What's the best way to diagnose this using my tuning equipment?

[darcy]

You could swap the O2s between banks and see if the issue follows

[bubba68ss]

I am also getting a cylinder 2 misfire. But that is the opposite bank... Hmm

[joecar]

Have you checked for air leak on bank 1 exhaust header...?

Also, have you checked that the intake manifold is not leaking on the bank 1 side...?