Brett H

iTrader: (2)

I put my car on the dyno today to get my WOT A/F leaned out after spending the past couple days bringing the VE in using LTFT's within -5 to 0 as per all the writeups.

Well I was able to get the A/F at WOT to about 12.7:1 and gained 10 hp up top just from that but I found a strange problem.

Will the car was running on the rollers either in park, in gear with the brake on or running but off load, the A/F would drop to 14.7ish but then creep back up to 15.8 - 16.0 range every time. I added as much as 3% fuel in the VE and the A/F remained the same. I even put the stock VE table back in with the same result.

Does the PCM command the A/F to run that lean off load for fuel conservation or is something else going on? If it is a PCM controlled command to go to 16:1 is there a way to get around it?

The wideband was located in the drivers side rear O2 bung. I removed the stock O2 and left it plugged in and dangling under the car and did not turn them off in HPT. I have cats (Carsound highflows) with Mac mids.

Please can someone help me with this because the wideband says lean but my exhaust, O2 etc have so much carbon it tells me I'm rich?????

sixvi6-camaro

iTrader: (9)

off load there is Deceleration Fuel Cutoff (DFCO). It can be disabled in the tune by setting the enable temp to a very high setting, like 250*, so it doesn't come on during normal operation.

Frost

iTrader: (45)

+1

Also I'm not sure what kind of method that is for tuning... pulling out an O2 but leaving it active and then making changes around it? Just use the scanner and put the car in open loop.

SSpdDmon

iTrader: (10)

I thought he said he pulled a rear O2 sensor.

Brett H

iTrader: (2)

To clarify, I did all the VE tuning on the street with the O2s in. The rear O2 was removed on the dyno for WOT tuning which as I understand does not reference them anyway. I questioned pulling the O2 myself but the dyno guy said he does it that way "all the time"

So does the pcm actually try to run lean off load for fuel conservation?

SSpdDmon

iTrader: (10)

I think it's a side effect of heat soak. What were your IAT's at the time it was running leaner? I'd be willing to bet they were over 100*F.

Brett H

iTrader: (2)

On all 5 of the dyno pulls my IAT's were between 91 and 93'F. Also it was probably 90' + outside yesterday and the humity was extremely high.

Basically I want to make sure that it is safe to drive it this way without hurting anything because I am driving it about 2 hrs to race this weekend.

Also is 12.7 a good A/f for WOT in LS1's? I have read different opinions, some say 12.7 others say 13.3???? I know that when I went from 12.2 A/F on the first pull to 12.7 by the last I gained 10hp and as much torque. Unfortunately I ran out of time and couldn't pull more fuel to see if I gained anymore but do you think it would be worth trying to pull more in the PE table?

Brett H

iTrader: (2)

My other thought was to leave it at 12.7 A/F but give it a degree or 2 more timing which would lean it out anyway.

SSpdDmon

iTrader: (10)

I'd say 12.7 is good and leave timing alone. The fuel trims will compensate for changes in AFR at idle.

edcmat-l1

iTrader: (10)

Adding timing wont lean out the mixture. Only removing fuel, or adding air to a set amount of fuel, will lean it out.

radkon

iTrader: (2)

You want a little on the rich side up to peak torque (12.4 or so), then lean out to max hp (12.8 - 13.0 generally), then fatten it up a little past your peak hp for safety purposes