Turned on STFTs and they are off.....

[BigMike42]

I am currently running an SD tune on my c5 ls1. I spent the last week tuning my VE table...hitting as many cells as possible in as steady state as I could get on the street. I tuned this using a VE Lambda error histogram...I did a conversion in hptuners to display my dynojet wideband in units of Lambda. Yes I had my trims and fuel cutoff disabled . I got everything dialed in very nicely...between .99-1.01 and I verified that across different days and weather patterns..it is rock solid according to my wideband and the car runs VERY smooth. No bucking...I can cruise control at 900 rpms in 6th...the cam is a 227/235.

So today I turned back on my STFTs (I don't use LTFTs) and they were off as high as -12% in some areas! So I figured, ok maybe my lambda calculation was off...so I did another log just logging raw AFR values (again with STFTs off) and every cell I hit was hovering around 14.7 AFR, so I was just about dead on. With the STFTs turned back on, my AFR was consisently in the mid 15s!

A week ago, before I began tuning, I did get the 02 heater codes on both banks, but the code cleared itself and never came back a day later. Could my 02s just be on the way out or is this normal behavior for having headers and a cam? I see people like to run the corvette rear 02 sensors and run an adapter. Could that be my solution? Or should I just run OLSD?

[HoP]

Your correct, it's a discrepancy between your wideband O2 and the old narrow bands.

[Russ K]

Also in closed loop, the evap purge valve will open, causing negative fuel trims.

Russ Kemp

[turboDave]

I've been experiencing the same thing. Is it okay that the narrow bands are off that far and pulling out that much fuel? Will putting new narrow bands in fix that?

[LSxpwrdZ]

Also in closed loop, the evap purge valve will open, causing negative fuel trims.

Russ Kemp

I wish we had control of that because I've been watching this really closely on my dyno and once I get open loop lambda dialed in within 1% error I'll turn closed loop back on and fuel trims are usually perfect for about 10 seconds and then all of the sudden you'll see them take a nose dive up to -20% then taper back off up to around -10%.

I believe there is a EVAP correction or airflow table to help combat huge swings in fueling but I could be wrong. This is why I alway's take the EVAP solenoid off all my car's and block off the evap line.

[BigMike42]

I wish we had control of that because I've been watching this really closely on my dyno and once I get open loop lambda dialed in within 1% error I'll turn closed loop back on and fuel trims are usually perfect for about 10 seconds and then all of the sudden you'll see them take a nose dive up to -20% then taper back off up to around -10%.

I believe there is a EVAP correction or airflow table to help combat huge swings in fueling but I could be wrong. This is why I alway's take the EVAP solenoid off all my car's and block off the evap line.

So is the correct way just to tune with STFTs then?

My heater codes came back on both 02 sensors...I am going to replace them.

[Russ K]

This is why I alway's take the EVAP solenoid off all my car's and block off the evap line.

Not a good plan, how are the fuel vapours removed from the charcoal canister with the Evap purge solenoid removed/capped?

Russ Kemp

[Russ K]

So is the correct way just to tune with STFTs then?

My heater codes came back on both 02 sensors...I am going to replace them.

Did you check for power & ground to the O2 heater circuit? Open fuse? Never seen both O2 heaters failing at the same time.

Russ Kemp

[BigMike42]

You guessed it Russ, it was just the fuse. All looks good now...I didn't log STFTs but my wideband is now reporting smaller switches...idle is going 14.6-15.0 now. I am happy that I didn't have to stop $160 on 02 sensors.

[LSxpwrdZ]

Not a good plan, how are the fuel vapours removed from the charcoal canister with the Evap purge solenoid removed/capped?

Russ Kemp

They arent lol.