89 testarossa

This seems a little too consistent. Are you measuring this "unplugged" value on the sensor wire (correct) or the harness wire (incorrect)?

Also, the O2 sensors only have meaningful outputs when they (and engine) is warm (i.e., coolant temp above about 160 deg F on the gauge). Since you got some "change" when you plugged the O2 sensors back in, I'd guess you did meet this condition, but I just wanted to mention it so you know to have the engine warm to use these signals.

 

i must admit when i have been an idiot i think i did test the harness side! bear with me please

 

Hey I got a chance to re test those connections after a lenghty drive when everything was nice and warm! I made sure to test on the sensor side and got a varying reading from one in the range of .25 volts to .70 v the other one just sat steady at .18v I have no clue which one is left and right they are colour coded with white boot and black boot thats it for markings . why would they have unhooked them? and is it even possible for them to have tuned the mixtures with them unplugged good news is the slow down lights are fixed and have not had any malfunctions yet they do a test when you turn the key then go off so i am assuming they are functioning corectly and will hopefully tell me before the car burns!

 

You set the mixture with them unplugged.. thats the way its done. Once the o2 sensors are plugged in they continue to feed the ecu with info so it can adjust accordingly.. the key is to get the car spot on with no o2 sensors...

R

 

Steve Magnusson, you are the best!!!! I hope you never leave us.


Ago

 

+1.. I'm just glad his wealth of info is free.. lol..

R

 

Totally agree with you guys everyone here has been great with the help!!

IF the car is suppose to be tuned with o2s unplugged why would ferrari have taped them up and left them unplugged and should i reconect them and see what it does? Im waiting for a service manual to show up then maybe i can get into this a little further!

thanks a million guys

Justin

 

Maybe I should change that policy

Justin -- Sort of odd results that definitely indicate things aren't quite right. When the O2 sensors are unplugged, the amount of fuel delivered should be quasi-constant, so the one having a variation from 0.25 to 0.7V seems an unusally large variation for the open-loop condition. If the O2 sensor is working, the one at 0.18V steady is indicating lean (but staying steady to within .01V seems too steady to be a real value). Open-loop you should expect some variation, but not a lot. You are really back to post #14 -- your next step should be to see if you can manually tweak the mixture screws and get the (unplugged) O2 sensor voltages to go from ~0.2V (lean) to ~0.8V (rich).

You didn't post what the voltages read if you plugged in the O2 sensors -- do they "wander" correctly around 0.5V, or are the stuck at some odd value?

One reason someone might unplug the O2 sensors is if there is a fault in the closed-loop operation (bad injection ECU, faulty ground causing injection ECU to do weird things, etc.). Additionally, it's the only way you can "force" a US TR to run lean -- for example, if you are trying to pass an emission test. My own TR had a fault in the wiring harness causing the ground at the injection ECU to (wrongly) be at ~0.4V. Since the injection ECUs try to keep the O2 sensor voltages at an average of 0.5V above the ground value, this caused my TR to run rich at idle (as the injection ECU would intentionally try to keep the O2 sensor output at ~0.9V with this ground offset error) -- not saying that this is your problem, but it's an example of why someone might unplug them in an act of desperation