Does anyone know the closed loop requirments for a 93 trans am? Do the O2 sensors have to come up to a certain temp? Would running long tubes w/ non-heated O2 sensors about 3 inches away from the end of the pipe cause the O2 sensors never to come up to temp, therefore causing the PCM never to go into closed loop mode?

 

are you not getting closed loop or what?

 

the headers are hot as hell after warm up so I wouldnt worry bout the temp on the 02 sensor.

closed loop requires:
coolant temp sensor in operating range (170-230)
02's active (crossing over .500 back and forth)

 

Yes, it can be a problem, and is not unusual on the 93's with the single-wire (non-heated) O2 sensors on long tubes. You might want to try a "search".... I believe a number of people have converted to 3-wire heated sensors to solve the problem.

The sensors need to reach about 600degF to become "active". At low engine loads, its entirely possible that a sensor in the collector of a set of long tubes will not achieve that temperature.

The requirement on coolant temp is a variable, but is generally in the range of 120-140degF. Additionaly, there is a timer from startup, that typically takes about 2 minutes in hot weather, and a little longer in cold weather.

 

A buddy of mine just put a hot cam and ported heads on his 93 LT1. He also put a set of long tube headers on. He does not have a Y pipe yet so he is just running straight headers. When we first fired it up it sounded and ran great. I was then looking at the scanner and it never went into closed loop. One O2 sensor started to move a little, but the other never moved much. Once it warmed up, it started to back fire so we shut it off. I think the O2s are not getting hot enough to function properly and will never get into closed loop. Im not sure about the backfiring. We check the valve lash on one side and one was loose. Gonna check the others next time we work on it. Could the long tubes with out heated O2s cause the staying in open loop?

 

Running with open headers totally screws up the O2 readings, in addition to the heat-up problem. Not a good idea. If they did get hot enough to go into closed loop, the fresh air mixing with the exhaust at the collectors would cause a false "lean" reading, the PCM would pour in extra fuel and it would run extremely rich.