3 wire O2 sensor operation?

[Russ]

Should a three wire O2 sensor go into open loop every time I decelerate? Engine is BBC 489 in my 88 crewcab dually. I have tried a Bosch and a Delco AFS-74 and both of them will go into closed loop when I accelerate, but will drop back to open loop as soon as I decelerate or come to an idle. I was under the impression that the purpose of a 3 wire heated sensor was to keep it in closed loop as long as it has 12 volts going to it? I have double checked for power and ground and they are both good. Sensor is mounted in the collector portion of my headers. Am I just not understanding the operation or is something not working right? It is odd that they both do the same thing. Thanks for the help,

Russ

 

[bigblock72]

The computer (specificly the prom) controls when it's in closed or open loop. The three wire sensor would allow the computer to switch to closed loop sooner than an unheated sensor would but the PROM will need to be reprogrammed to take advantage of it though. Are you trying to fix a drivability problem with the sensors? I would assume the PROM has been changed to work with the 489 and may have been changed to have an open loop idle, which is common with a motor with a large cam and heads.

 

[Russ]

Brian at TBIChips burned the chip for me after I put the engine together. I was just hoping to fix a slightly high idle/running rich problem I have after driving at speed. You are probably right though and it has been programmed to switch to open loop.
I would like to be able to run more fuel pressure, but am unable to as it causes idle problems. Thanks for the help,

Russ

 

[southernspeed]

Brian at TBIChips burned the chip for me after I put the engine together. I was just hoping to fix a slightly high idle/running rich problem I have after driving at speed. You are probably right though and it has been programmed to switch to open loop.
I would like to be able to run more fuel pressure, but am unable to as it causes idle problems. Thanks for the help,

Russ

yeah sounds like he's set it up for open loop DE (possibly) and idle.
You can't just up the fuel pressure without altering the pulse width or you'll 'overload' the injector for it's current setting. Sounds like you either need to enter the dark world of tuning or talk to him and email him some data logs to get another chip burnt. To get anywhere near right you'll really need to install a wideband controller so Brian can see exactly what's going on. Even then he's only ever going to be able to do you a 'best guess' chip. The only way is drive/data log/tune.

 

[Russ]

I have been trying to avoid the dark world of tuning. I am 45 years old and did not grow up in the computer era. I decided to retire from the Navy because after 25 years my job had turned into a desk job driving a computer. I have actually tried to read up on the tuning stuff a couple of times, but just do not have the patience to sit at a computer screen and try to understand something that really does not make sense to me. I may have to give it another shot though. Thanks for the help,

Russ

 

[southernspeed]

Hey you've only got 2 years on me and I'm learning it!.......slowly!