O2 sensor feedback?

[Dave]

How much O2 feedback does a SMEC use during open loop operation? The only reason I ask is because I'm having a problem idling and part throttle fuel control. It's pretty rich all around and the idle hunts around 13.1:1 - 15.1:1. Even during open loop it does this which makes me wonder if our SMECs use any O2 feedback at all. I know OBD2+ use about 10%.

[turbovanman²]

Open loop, the sensor is ignored and also at WOT.

From the courses I've taken, OB2 is also the same but because there heated, they go into closed loop very fast for emissions.

[Dave]

Open loop, the sensor is ignored and also at WOT.

I thought so, but thank you for the assurance!

[shadow88]

It's not so much how much "say" the O2 has in closed loop. It's tries like crazy to acheive 14.7 give or take. The way it does this is altering the injector pulse width and showing how much it's changing it in the short and long term adaptive memory.

Now assuming you have +40's and you turned the fuel pressure down to 27 psi static, the computer should have no problem maintaining stoich. However, if your fuel pressure is higher (most people seem stuck at 32psi) the computer will have a hard time adjusting the correct pulse width and it'll show as the rich a/f ratios you have on your wideband display.

Keeping that in mind. Once you mash the gas- all is forgotten by the smec and you'll get all the fuel you have tuned for. Chances are good, you (like me) can't get the fuel pressure low enough to run at 14.7:1.

[Dave]

It's not so much how much "say" the O2 has in closed loop. It's tries like crazy to acheive 14.7 give or take. The way it does this is altering the injector pulse width and showing how much it's changing it in the short and long term adaptive memory.

Now assuming you have +40's and you turned the fuel pressure down to 27 psi static, the computer should have no problem maintaining stoich. However, if your fuel pressure is higher (most people seem stuck at 32psi) the computer will have a hard time adjusting the correct pulse width and it'll show as the rich a/f ratios you have on your wideband display.

Keeping that in mind. Once you mash the gas- all is forgotten by the smec and you'll get all the fuel you have tuned for. Chances are good, you (like me) can't get the fuel pressure low enough to run at 14.7:1.

What a lot of people don't realize is that, even though our cars are OLD, they are very intelligent for their time. They can pull or add up to 33% corrective fuel trim. Mine, on the other hand, at 58psi base was pulling all of that 33% away under the long term fuel trim. I was able to achieve 14.7:1 while crusing. Not bashing what you say at all, you are correct, but the SMEC or SBEC's are very intelligent components and can adapt very well for their time, IMO.