When I start my car (1990 396 c.i. vette SD 727) the car don't idles.. I have to use a bit a gas pedal to help it to stay at idle. Progressively I can slowly remove my right foot from the gas pedal (very slowly..) and it idles.
Always remaining stopped in the garage (without put the car in gear) I can hear the car going in closed loop. (I checked with datamaster and the car starts immediately to idle perfect) .Once in CL, the car idles perfect. (I removed some fuel at 55-60-65 MAP at 800-1100 rpm from the previous 383 calibration and with a LPe 219 cam... now I have a 230-236 112 LSA with more overlap).

How to remove fuel only in cold Open Loop at idle?
Thanks
-Beppe-

 

Sounds like the open loop calibration may be off. Either the VE values are too low/high, or the open loop commanded AFR is off. Try setting your VE table up in that area with the engine warm and see how it does cold. You may have to raise/lower the commanded AFR and add a little extra idle speed when its cold to improve teh idle.

 

should the the open loop commanded AFR changed with the tables:
Loop Open Change % AFR Vs. MAP and
Loop Open Change % AFR Vs temp?
I have stock values on these tables
...Or I have to change something else?
The VE values on the Idle area seems correct (I removed a good amount of fuel in this area and in closed loop it idles good).
Thanks
-Beppe-
----------
....There is also a constant called:
Idle Open loop % Change AFR .. but the % change is 0 also in the stock bin.
-Beppe-

 

Sorry I made an error...
I edited the original title of the thread from " How to remove fuel only in cold CL at idle?" to the right one:
"How to remove fuel only in cold OPEN LOOP at idle?"

Any tougth on rmove fuel at idle in OL ??
Thanks

 

Whats teh BLM during closed loop idle? That will give a rough approximation of what the fueling is like in closed loop. From the sound of it, the engine is either too lean (<14.7:1 from the sound of it), or WAY rich.

 

During closed loop it's dead 128 at 900 rpm in drive and 126-128 at 950 rpm in Neutral.
the Open loop seems way rich to me.

 

Hmmm... Whats teh commanded AFR in open loop at cold temps around idle? Is it worse for the first few seconds of operation?

 

Commanded AFR in OL ?
if I see DAtamaster it's around 14.00, then slowly goes to 14.73 when it warms and after 180 secs enters in closed loop.
I think it's the stock enrichment added in OL...
For this reason I want to know HOW to remove fuel in OL (or HOW to reduce the commanded AFR in OL)
-Beppe-

 

Can you post a pic up of the table? Also, what do the BLMs do when the engine first enters closed loop? Does it drop, or rise? That will tell you for sure if its a lean or rich issue. If its around 14:1 at modest temps, then you likely need to lower the AFR (richen the mixture).

 

I repeat: When I start the car, the commanded AFR I can see in Datamaster (not the real AFR) s around 13.xx (just the stock enrichment at start up).
Just few seconds after it is 14.00 then 14.10...14.30 during warm up in Open Loop.
It is in OPEN LOOP, so the BLM/INT are 128/128 ! When it enters in CLOSED LOOP, the BLM stay at 128 with sometimes a INTof 130 sometimes at 126 .
Once in closed loop you can hear the idle stabilize. sometimes the BLM at Idle in CL is 126.
I have a NON heated O2 sensor in the long tube headers. When the temp on the headers drops, I can see in datamaster that the O2 cross counts stops, and the O2 readings stays in the high value. and the idles becomes unstable (just because it exit from closed loop and -I think- it enters in Open loop again using the OL richer mixture).
I tap the gas pedal to raise the temp in the headers and the O2 starts to be alive again, the cross counts starts again and the O2 voltage starts again to go from high to low.... and the Idle satibilize again in CL.
My assumpition is it's rich...
My main Question: How to remove fuel from OL idle?
If my assumption is wrong and the OL idle is lean, Id like to know How to ADD fuel in OL idle.
-Beppe-

 

Im not real familiar with the $8D, but there should be a table of open loop AFR or % AFR vs. MAP and cool temp. Setting the values at low to mid maps and lower cool temps to numerically higher AFRs will lean it out during OL idle, lower will richen it. FWIW, 14.1:1 is fairly lean for cold idle. Probably 13-13.5:1 would be better. It may even want to go richer then that, depending on how the motor acts at low temps.

 

These are the tables i asked on post #3.
I try to lower these values at cold at the maps values where the car idles.
-Beppe-

 

Ok I drastically reduced these 2 tables.
These two tables (if i correct understand) reduce the fuel added when in open loop, and the addiction of fuel (to change the the target AFR ) is in % of change. I thought: If at 55Kpa the stock % value is 5.08 , I have to assume that for OL the ECM is adding about 5% richer than stoich (or better a 5% correction on the AFR).
The same is for the other table, that is in relation to the coolant temp.
an example is that at 32°C the change is 9.77% for a total on my idle of about 15%.

Ok ,I drastically reduced these 2 tables just to have a minimal correction (about 5% total).
The car idles very good now in OL (confirming my feeling of rich situation in OL at idle).
Now I'm looking at a Datalog I made with new corrections .
The Target AFR on datamaster is about 13.xx in the first 15 secs (probably due to the cold start routines), then progressively start to climb over the 14.73 value ending at 16.xx (!!) before to enter in closed loop.
Ok, I reduced the correction, but I left some positive % correction.
Could someone explaine me why the target AFR changed so much up to the point to cross the stoich value? (even considering that now it's idleing good).
What I'm missing?
Thanks.

-Beppe-

 

Any thought on this from you gurus?
Thanks
-Beppe-