troopercar

iTrader: (6)

Please excuse me if this is a stupid question. I am tuning a 98 vette. 23x, .59x, 114lsa, ported 243's, 90mmls2 tb, fast 90.

The car runs great, everything is perfect, follows the commanded afr as per wideband.

Here is the issue, at idle it goes nuts and dies at stoich. If I command 15.7 it idles beautifully. The only problem is the stft's keep adding fuel to get it to 14.68 and it starts surging until it dies. This thing otherwise runs perfect but will NOT idle at 14.68. At 15.7afr per the WB it idles awesome. I have tried everything I can think of.

20deg timing at idle, more or less and it gets worse.

I guess the question is can I get it to idle at 15.7afr? If not what needs changed to make it idle at 14.68? Base airflow? Tried that, but I know I have to be missing something.

WeathermanShawn

iTrader: (1)

You could change the O2 Switchpoint to read a lower value than stoich (450mv). Try 350-375 mv. Its the only way in closed-loop I have found that will reliably change an Idle AFR. With it lower you will get less + switching.

There may be some other way, but again in closed-loop I have found that trick to work.

gold98Z28

iTrader: (7)

open loop idle. or open loop period... you have a WB, make it fuel the way YOU want it too

LS1-450

iTrader: (33)

What do you mean, it gets worse? If the timing is dropping, then you need to look @ your spark tables; Idle & ECT. If either or both are pulling too much timing due to flare control, over/under speed or ECT, then that is contributing to the problem.

troopercar

iTrader: (6)

The timing is steady. I mean adding timing doesn't help it.

Actually, adding 5-6* timing in P/N helps a little but not in gear.

jimmyblue

iTrader: (11)

With a big cam like that you probably are blowing
intake air into the exhaust and fooling both narrow
and wideband sensors in the indicated-lean direction.

I'd go with the switchpoints, trying to get closed
loop to settle at the "happy place" you've found in
open loop. Use the wideband to see what the reading
is for "commanded_15.7", and try to get it the same
closed-loop (regardless of what value the meter says).

You want timing less than best, so that adaptive
spark has some upside authority. Like if you want to
allot 5 degrees to adaptive spark underspeed, then
set that up (eliminating any stupid discontinuities you
may find, along the way) and then give (best-5) to
the idle tables.

WeathermanShawn

iTrader: (1)

Like 'JB' says..look at those switch-points.

Something else I thought of. If it is really true that your STFTs are adding fuel at Idle..then that is hinting that your Base Airflow is too high? (I think I have that right)..

I agree that with these bigger cams that there is a false lean report from both narrow-bands and wideband O2 readings. You also have to ask yourself, is it only happening when the engine (ECT) is cold or all the time? I.E., are you positive that you are in closed-loop or are you still in the 'Commanded Fuel in Open-loop'? That makes a difference in advising you.

Nevertheless, I have found Idle O2 switch-points are the most responsive to manipulating. If you go to far, it may throw a DTC, but even 375-400 mv may solve your problem..