Spartan2 mostly cycles between rich and lean

Spartan 2
1

I’ve been running this Spartan 2 on one bank of my 302 V8 since 2016. The other bank is an Innovate MTX-L. Last year with no other changes the Spartan started spending most of its time at full rich or full lean.

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Green is the target, white is the MTX-L, yellow is the Spartan. Sometimes I will get a reading out of it, but about 4.0 richer than the other bank.

The engine runs great, there’s no way that bank is actually going pig rich or dead lean. I see 13.3 - 16.7 - 19.9 on startup as I should. I haven’t done the free air or lighter tests yet, I should be able to get to those tonight. If the cables will reach, I may swap sensors between banks and see if there could be something going on with that bank or header.

Any other reason you’d expect to see odd behavior like this?

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Probably a sensor issue, post your results from swapping the sensor.

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Free air test was ok. Did the lighter test and got erratic results. I bought a replacement sensor from you last week so I swapped it on and saw much better results with the lighter test. Unfortunately the 14point7 sensor pigtail was much shorter than the Bosch 17025 I originally bought so I had to stretch some wires to get everything to fit, and I had no choice but to swap banks.

Spartan 2 now AFR, MTX-L is AFR2. Tracking is much much better, the sensor must have just had it after 8 years.

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Thank you!