I tuned out a camaro today with a 7730 SD AUJP bin file today and everything went fine once we changed the MAP and o2 sensor except for my idle AFR. No matter what table I would alter the car would start up at 12 AFR and then as soon as the computer closed loop it would climb to 18 AFR and stay there until you rev the rpms. The fuel pressure is fine and the injectors are 24lbs. When we ran the car on the dyno I was able to smooth out the AFR to what the engine wanted for max torque. What
table am I not correcting right and what should the setting be close to on a 383?

Help!
Frank Reckenberg

 

The AFR value is calculated and next to worthless, if you're tuning stick with BLM readings in closed loop.

 

I think he is talking about a WB 02 not the calculated AFR.

 

That is correct regarding the wb on the dyno. My Diacom GM Plus was showing everything fine at idle yet the wb on the dyno was showing around 12 AFR until the computer kicked in on the car then it takes the AFR up to 18 AFR regardless of the ajustments I make in the VE tables. While running the car on the dyno the AFR will be almost perfect once I start taking the RPM's up. The fuel pressure is at 43.5 at idle and if I increase or decrease the fuel pressure it has no impact on the idle. The cam isn't that agressive.

Frank

 

How agressive is it?
duration/LSA?

 

Ah, my bad, didn't catch that you were WB sampling AFR. I've seen very similar problems when the regular O2 sensor was malfunctioning...ECM was leaning the engine out but reporting low BLMs like it thought the engine was running rich.

Root cause was a failed head gasket leaking coolant into #7 cylinder. The coolant, which contains silicates, contaminated the O2 sensor and caused it to report higher voltages (rich) than actual, causing the ECM calculate lower BLMs and pull fuel out. I found reference material thru Google showing coolant-related O2 sensor failure modes identical to what I observed.

I'd say your new O2 sensor is suspect. Check ALDL data to see if the ECM is deliberately reducing fuel delivery, and if the O2 sensor behavior is out of whack versus the WB sensor. If so, pull the O2 sensor and look for signs of contamination...white crystalline deposits were what I found on mine. If the sensor is discolored, find the root cause. If not, I'd swap in a Delco O2 sensor (like Grumpy, I don't like Bosch or other aftermarket O2 sensors) and re-test.

-Kevin

 

...and even if the onboard O2 sensor isn't fouled, if it's an aftermarket piece I'd still swap in a Delco one and retest.

Members of the LT1 and LS1 communities reported getting SES codes and slight engine misbehavior running brand new Bosch O2 sensors, which cleared when Delco sensors were swapped in. No doubt the Bosches are high quality, but there's enough data to push me toward Delco sensors.

 

Thanks for the input guys....the bosch o2 sensor is going to get changed!


Frank