Fixing 02 codes through tuning?

[Zfreak]

I have a modded 1997 LS1 with ported 243 heads, ls6 intake, 228/232 cam, Vararam, and most importantly a set of LG Street LT's with cat deletes, X pipe and z06 Ti's.

My problem is that I can't for the life of me get my 02's to "switch" properly. It's almost like I dialed in the tune so well (my ltft's are all -.08 in most of my operating range) that they're not hunting around in different cells and changing the fuel mixture.

I have tried replacing the sensors multiple times, they will usually not throw codes for a few days but lately they've been starting to throw codes within one drive cycle. Wiring is good, heater fuses are fine. O2 readings DO oscillate properly (approx .2 to .8 volts) but definitely not much at an idle. I'm sure the LT's are causing the problem by locating the 02's further from the exhaust and allowing it to cool (and there is less flow thru the same area due to the larger diameter). I have tried the hold drilling trick, but there was zero change.

The 02's work fine and peg right around 880-900mv when at WOT (which my LC1 says is approx 12.5-13:1 afr) so I know they're giving proper readings.

Any ideas to play with the tune to get the 02's a bit livelier? I'm thinking maybe adding spark...but I know too much can be dangerous.

[Zfreak]

FYI, the codes I'm getting are: P0133, P0153 (these slow response ones are normal for LT's), P1133, P1134, P1153, P1154. I have the rear 02's mounted in the FRONT positions (supposedly they have better heaters for this sort of prooblem).

Does playing with the 02 switch point help the time ratio and switching errors? I would guess yes but wondering if people have specific suggestions first.

[joecar]

Unplug the NBO2 connector, and measure the heater voltage wrt to heater ground and verify that it's the same as battery voltage... if it's lower, then there's some resistance in either circuit (check grounds).

[Zfreak]

Hmm, I've been thru the grounds but good idea! I'll check that out and see what's up. C5's are famous for electrical gremlins...that could definitely be one of them!

[dc_justin]

Could the problem be mechanical and not really a "problem" at all?

The cam you're running has a larger than stock duration, and likely has a decent amount of overlap (didn't list the LSA). Wouldn't it be reasonable to assume that at low rpm, that overlap is causing some of your unburnt mixture to escape into the exhaust and cause the O2 sensors to pick up on that?

[Zfreak]

The cam has a 112+4 LSA. I'm sure there is some overlap there.

The problem is that the 02's aren't oscillating like they should. One thing to note is that the same cam has been in there for almost a year and I didn't throw many 02 codes for the first 6+ months. It seems to have fewer problems in cold weather (which doesn't make sense). I still need to look at the grounds, that is something I haven't checked specifically in relation to the 02's.

Today I jumped into my 02 switching tables and noticed that there is a huge dip in there, it goes from 450mv to 380 and then up to 525....the stock cam might have liked that but I'm guessing the lumpy cam forcing different cells all the time is moving between cells more. I have gone to 450mv across the board up till CL mode 40 and then it climbs to 475, similar to how stock was. I need to do some reading on here about CL modes...I wonder if its something I missed changing when the cam went in.

[Zfreak]

I ran the test that joecar indicated and I found I was only getting ~7 volts at the sensor! I cleaned one ground and I removed the splice pack for the other and soldered everything together onto an eyelet and now its at a solid 12+ volts. I went for a quick spin and the 1133 and 1153 codes didn't pop back up immediately like they usually do. I'll be taking it to work tomorrow. If I don't throw codes the whole way to work, I'll consider this a huge step forward! Thanks for the advice.

[Highlander]

Which Ground?