LS1 ruunning rich on Bank 1

[MTT700]

Hi,
I have an issue with a 2002 LS1 (from a Firebird). It is running rich on one bank, Bank1, in closed loop only (runs fine cold in open loop).
I first tried switching the existing O2 sensors sise to side and that made Bank2 deteriorate and run rich, but did not improve Bank1.

I have replaced the MAF and the two O2 sensors with OE parts. Bank1 continues to run rich. I have taken off the fuel rail and tested it and it operates perfectly.

Can anyone shed any light on what I should try next, or if someone can offer a service to resolve?
Thanks so much for reading.

[Cutlass]

any modifications to the engine?

[MTT700]

No modifications to engine. Has Street & Performance reprogram the ECM for tire size but kept emissions intact.
Have had to replace OE log manifolds with custom to clear suspension.


Aftermarket cats (one month old).

[Cutlass]

a leaky weld on that manifold could cause outside air to enter the exhaust and fool that O2 sensor into thinking that bank is lean and cause it to dump more fuel in

[0rion]

a leaky weld on that manifold could cause outside air to enter the exhaust and fool that O2 sensor into thinking that bank is lean and cause it to dump more fuel in

+1

[Frost]

What these guys said.

.. Has Street & Performance reprogram the ECM for tire size but kept emissions intact....

I hear that's pretty expensive

[01ws6er]

+1

Or a blown out manifold gasket

[katelyn2005]

Yeah