DanielRicany

Hey guys. I have a 1985 Corvette and I was just wondering what AFR I should shoot for during open loop. I believe that it's supposed to be richer in open loop than when in closed loop, or is it temperature specific?

Thank you!

MrWillys

Observe your closed loop blm, and tune to 124. This way it will always be slightly rich.

Cliff Harris

I've seen numbers in the 12.5 to 13.0 area. You definitely want it to be rich or you will have trouble with detonation.

BLMs mean nothing in open loop mode. The ECM sets them to 128 and uses the fueling tables. PE (Power Enrichment) and AE (Acceleration Enrichment) are the parameters that are most important during acceleration.

MrWillys

While Cliff is correct about WOT operation I would be very careful about tuning to 13:1 afr, because it is very close to being to lean. Lean best torque is at 12.5:1 and if tuned to this and weather should cool it could go leaner. I always stay between 12 and 12.5 to keep it from coming apart. As previously stated, tuning to 124 blm will assure a slightly rich mixture upon startup until closed operation parameters are meet.

At WOT look for .860 volts or greater.

MikeT 90 C4sixer

The OP asked about tuning in open loop, not WOT. they are not the same thing. When an engine is cold, it starts out in open loop, until things heat up, and the O2 timers run out, then it goes closed loop. Now if he asked about WOT, then yes, shoot for 12.5 AFR or richer. Otherwise what the fellas said above is all good.....

cumbercr

Idle AFR in open loop varies with coolant temperature. At startup the AFR will be the richest and then leans out as the coolant temperature increases. When the closed loop timer times out, the ECM goes into closed loop. The timer can vary from 50 seconds (hot engine) to 300 seconds (cold engine). So there's no simple answer to your question.

Street Lethal

14:2 is stoich w/ethanol mix, so there is no lean condition with 13:1 air/fuel ratio. The problem with a 13:1 air/fuel ratio is due to intake temperature as there is a radical in pump gas that causes detonation when a certain combustion temperature is realized, but if intake temps remain ambient or less, throughout the RPM, then it can't be too lean. The term too lean when less than 14:2 is a figure of speech due to carbs that have no O2 correction, or EFI's that have slow processor speeds, but 14:2 is stoich, regardless...

MrWillys

I think you may have misunderstood my post. I was referring to WOT operation where almost zero vacuum is occurring and the vehicle has gone into power enrichment and open loop. It is no longer being controlled by the O2. Lean best torque at WOT is 12.5 AFR, and some tune to 13:1. This is somewhat dangerous to do unless it is constantly monitored.

Also, the lambda O2 adjusts correctly for both gasoline, and ethanol, and in closed loop will adjust the BLM accordingly. I know this after doing some research for running E85.

This guy made understanding the O2's operation for ethanol much easier should you chose to read it.

http://ls1tech.com/forums/fueling-in...r-ls1-e85.html