87tpi7749

Is this possible, 21.1 to a low of 17.1 AFR? Perhaps my sensor location? I installed it into the stock header (edelbrock tubular) location.

Engine is 385ci, Sportsman II heads 64cc, 8.5:1 cr, comp nitrous hp cam 274/292 .488/.501, 1.5 rockers, 30lb inj, 45psi FP, 52mm tb, stock runners & base (yes I know), crane HI-6 ign, $58 749 ecm, 2bar.

I'm tuning with charger belt off to get started. I'm just blown away by that AFR number. Exhaust burns my eyes. Lean misfire? I'm starting with a stock BBZB1580, adjusting from there. The motor doesn't seem to respond in an expected manner when adding fuel, AFR never goes down. BTW WB does test good.

Maybe I need to move that sensor downstream. Anyone got any ideas. VE suggetions based on motor size?

3.8TransAM

Im prolly going to have to say lean misfire at this point.

Although a header leak could cause the same scenario, its rich but the leak is making it see lean.

Are u absolutely sure everything on the car is right mechanically and electrically? Can be a real PIS trying to tune around something wrong or broken(we've all done it at least once)

Sensor should be fine in the stock location.

Are u tuning in open loop or running the stock narrow band too?

Also, I believe the injector constant doesnt work on the 749 and u have to set it like u do on the TBI apps.

Give us all your details and im sure some other will chime in.

later
Jeremy

Willie

iTrader: (1)

Are you getting those AFRs in open loop or closed loop?

87tpi7749

I'm running open loop as the NB is not installed. I figured by bpc to be 150 using the bpc calc utility on Craig's site. So I have used the tdf editor an changed the bpc vs des egr field to read in real numbers. So I have set bpc vs des egr to 150. Motor likes it better at 128???

Absolultely no exhaust leaks, using new ceramic coated headers and dead soft aluminum gaskets. Motor is absolutely perfect mechanicaly. Base timing set correctly to match constant of 0 deg. Injectors are recent installs. Rotating assm is all forged, 4340 crank, manley sportsman 5.7 rods, srp -31cc dish pistons, balanced, its a GM Bowtie block.

What besides bpc vs des egr will add/sutract fuel at idle closed throttle? Which way do you go with VE to add/subtract fuel.

Should bpc vs des egr be set and thats it, don't adjust this again until you change injectors?

Are my 30's too small?

Willie

iTrader: (1)

Yep, I posted about the same "problem" late last year. Look at the following tables:

Open Loop AFR &
Open Loop AFR - Closed Throttle.

The verbage may be different depending on software and version.

Modify these tables to values I've used in the pic and see if that helps. I was also running very lean in open loop and with this change, the AFR's have richened significantly. I've also found that I run slightly leaner (about one point) than the tables values.

Willie

Willie

iTrader: (1)

As for your question about BPC vs EGR, these values should be set once and left alone. Think of it as the injector constant.

Willie

86and96

Are you running without an alternator? You could be in battery voltage correction mode if you are.