Longtubes and O2 Sensors

[88-GT]

Well my mods are listed in my sig as well as I recently added a taurus fan.

The problem lies in some drivability issues with hesitation when it is initially warming up. It rarely ever does it warm, when warm it runs great. I have pulled codes but to no avail. I also have been getting terrible gas mileage, the last tank I was getting 11mpg, all city of course but still no good.

My latest idea was that when I got my longtubes they did not have the o2 sensor bungs so i had a shop weld them in the collectors, which are 3 inch. I was maybe wondering, since most of my problems are at low rpm's, that they are not reading correctly for whatever reason.

Is it possible that they are not close enough to the center of flow or maybe even too far away from combustion to read properly? Thanks for any help.

 

[2000 blown conv]

Well my mods are listed in my sig as well as I recently added a taurus fan.

The problem lies in some drivability issues with hesitation when it is initially warming up. It rarely ever does it warm, when warm it runs great. I have pulled codes but to no avail. I also have been getting terrible gas mileage, the last tank I was getting 11mpg, all city of course but still no good.

My latest idea was that when I got my longtubes they did not have the o2 sensor bungs so i had a shop weld them in the collectors, which are 3 inch. I was maybe wondering, since most of my problems are at low rpm's, that they are not reading correctly for whatever reason.

Is it possible that they are not close enough to the center of flow or maybe even too far away from combustion to read properly? Thanks for any help.

I would agree with not close enough to combustion,,I had to have new bungs welded in, there were in my collectors and they were moved closer to the motor. My car now idles better,,less hesitation and seems to run smoother in general..If you would llike I can take a pic and show you where they were moved from and where they were welded in,,just let me know..

 

[Daggar]

I think that the tempurature of the sensors are what causes the trouble a lot of times. Once the pre-heat cycle of the sensors is complete, they rely on exhaust heat to keep them at operating temp. The further away from the heat source, the more likely you are to have problems. I do not believe (although I am not certain) that once the heat cycle ends, that the sensor heat will activate again until the motor is shut off and restarted. I think you hit the nail on the head when you said that when it's good and warmed up that it all acts fine.

 

[Daggar]

Hissin50 or Michael Yount... can you verify the sensor heat cycle?

 

[emagdnim]

I thought the computer doesnt even use the o2 sensors while its in open loop right when the car is started so how can the sensors be at fault? I would think that if you had problems while the car was in closed loop while the computer was tweaking the mixture based on the o2 sensors then that would mean they are to far back. Im confused then...

 

[Daggar]

I thought the computer doesnt even use the o2 sensors while its in open loop right when the car is started so how can the sensors be at fault? I would think that if you had problems while the car was in closed loop while the computer was tweaking the mixture based on the o2 sensors then that would mean they are to far back. Im confused then...

You are correct about the computer defaulting to open loop when cold. However, if the 02 sensors are continually out of range once the car warms up then the EEC will not enter into closed loop at all. Instead it will continue to run premapped fuel and spark tables. he says it all acts pretty good when the car is good and warm. This suggests to me that those are times when the EEC actually makes it into closed loop.

 

[emagdnim]

Ok thanks for clearing that up i wasnt sure what made the computer go into closed loop i thaught it might have been a temperature sensor or something like that! This thread interests me because i also have the headman longtube headers with the o2 sensor welded into the collector and dont seem to have problems with idle cold or hot other then the fact it idles a bit faster hot. Looks like we are both SD also.

 

[Daggar]

The temp sensors also have a part in the EEC going into closed loop. There a number of things that have to be "right" in order for the EEC to swap modes.

 

[88-GT]

I would agree with not close enough to combustion,,I had to have new bungs welded in, there were in my collectors and they were moved closer to the motor. My car now idles better,,less hesitation and seems to run smoother in general..If you would llike I can take a pic and show you where they were moved from and where they were welded in,,just let me know..

Yea pics would be sweet

I am also starting to lean even closer to this theory. Cause it almost seems to run its best one initial startup. Like the first 5 mins of driving, could this be while it is still reading the preset curves in warmup? I hope this could be my problem, tried just about everything else.

 

[88-GT]

Oh and I also forgot to mention that the o2's are less than a year old and are Bosch brand so I doubt them being worn out would be the problem.

 

[Daggar]

You might be suprsied how quickly O2 sensors deteriorate when sitting in the exhaust stream when not properly heated. It's not to say that yours are toast already but don't be suprised.