Split BLMs, exhaust leak, and O2 sensors

[Craig 94 TA GT]

I'm still fighting the issue of split BLMs. Everything still points to an exhaust leak at the collector, which I've been trying to fix for a long time. All that I've been doing is making it worse. Now I'm seeing a constant 5 degrees of KR at idle. I've tried Felpro 60986 2.5 donut gaskets, but the leak is now worse. I even tried using lots of copper RTV to seal, but that didn't help at all. I think I'm going to try SLPs original collector gaskets again. Otherwise, I don't know what else to do, to fix the leak.

One other thing I noticed was that a scan after shut-down (car not running but key on) showed that the driver's side O2 was fluctuating between .142 and .147 volts. The passenger's side was a constant 0.089. Does this mean that there's something going on with one of the O2s?

[Joe 1320]

Percy's dead soft aluminum gaskets will crush around imperfect sufaces to seal the exhaust. The best out there.

[Trash man]

or u could try a slip on, but id get another drivers side O2, with the car off it shouldnt fluct. at all

[Kevin - Blown 95 TA]

Percy's dead soft aluminum gaskets will crush around imperfect sufaces to seal the exhaust. The best out there.

I think he's got donut gaskets.

The O2 sensor should not have a static reading - it is supposed to quickly fluctuate up and down from less than one volt to nearly zero volts. Logging software will usually just show it fluctuating randomly under a volt because it isnt sampling fast enough to log all the transitions. If it doesnt move once warmed up, then it's dead or there is a wiring problem.

[Craig 94 TA GT]

I ordered 2 sets of SLP donut gaskets, which are MUCH softer than the Felpro ones. In fact, the Felpro ones were so hard that you could take a screw driver and hammer to it, and it wouldn't even make a mark.

The original problem was that the y-pipe had an internal ring to center the gasket. SLP had originally welded it way off center, which cause it to leak and deform the gasket. I finally re-welded a new ring dead center, but thought the Felpros would work fine. Apparently even the Felpros with RTV did not. So hopefully the softer SLP gaskets with centered rings will finally eliminate KR and the huge BLM split. I just can't believe how a very tiny exhaust leak can cause so much KR - even with the LT4 KM.

Thanks for the tip on the O2s. I was just worried because I saw the voltage flucuating after the engine was shut down...yet the other O2 didn't move a bit. I thought they only flucuated when the engine was running.

Oh, and Kevin I was wondering one thing - have you noticed a split in BLMs due to a heads/cammed/aftermarket TB LT1? I also read that the split was due to more cam overlap and the design of aftermarket TBs. Just wondering if you ran into that before.

[Injuneer]

Are you sure you don't have a code (DTC 43) for a faulty knock sensor circuit. That will cause knock retard to be present almost all the time, since that is the way the PCM responds to the trouble code.

Try switching the O2 sensors side to side, and see if the "split" follows the sensors. That would confirm a problem with the sensor rather than the exhaust leak being the major culprit.

[Craig 94 TA GT]

Thanks Fred, I will try to swap the O2 sensors. It's such a pain to get to the pass side with the SLP design, that I'm really thinking of just getting a new one.

There are no trouble codes set, according to Freescan. The more I played with the header to y-pipe joint, the more I got KR. KR only showed up before when revving, and it was between 0.1 and 1.x degrees. Now it's 5+ degrees constantly. At least SLP waived their $25 minimum charge for me because of their poor workmanship on the y-pipe.