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Tuning open loop AFR in HP tuners.

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Hello. I’m currently running into an issue while trying to dial in the tune on my 2006 Corvette (E85 full-time) that I can’t seem to figure out. When I cold-start the car, it starts in open loop with a commanded lambda target of .66 to .78. Once the car goes into closed loop, the target lambda goes back to 1.0.

I am using an HP Tuners MPVI2 unit and their VCM suite software. I’m getting the target AFR numbers through the VCM scanner and taking a log during a cold start.

going through all of the available tables and parameters I can see, I don’t see anything that controls commanded AFR in open loop or for cold start. The closest I can see is maybe the Cranking VE table, which the previous tuner who tuned the car left with all cells filled in with the same values. Once the car is warmed up, hot restart seems to be ok, with the occasional surge when I restart the car after it’s been sitting and cooled down a little. I can deal with the surge for now. But, with the commanded AFR being so rich on cold start, I’m seeing oil temps drop while coolant temp rises until I get into closed loop. Once in closed loop and the AFR target goes back up to 1.0, the oil temperature climbs to normal operating temperatures as it did before the switch to e85.

Any help is greatly appreciated. I can post tune and log files if anyone needs them.

There's a couple of tables that come into play here depending if your issue is during cranking or during warmup. First up under Fuel - General you'll find a cranking fuel table that defines the commanded AFR during cranking. Once the engine is running the commanded AFR will be defined by the open loop gains. If you check under the Fuel - Open Loop/Base tab you'll find a range of tables that modify the commanded equivalence ratio based on aspects such as inlet valve and engine coolant temp. If you set these tables to 1.00 this should command a flat line lambda 1.00 during warm up however I'd recommend not quite going to this extreme as the engine will generally want a richer AFR target when it's cold. Make small adjustments until you get the commanded AFR where you want it.

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