Hi Guys,

I am helping my nephew to restore his 87 IROC (engine code F) to factory original status.

The problem is the system never goes into closed loop status.

Here is what has been checked.

NBO2 Sensor to ECU Connections. Signal and Ground (through headers).

ECU Connection to System Ground.

ECU Bias Voltage.

New Single Wire O2 Sensor.

How does the ECU utilize the O2 Vmax, O2 Vmin, and the Time qualifier parameters to determine if the NBO2 is ready for Closed-Loop Mode?

I looked at some datalogs (cold start) from a good car. It looks like the NBO2 voltage increases from the Bias voltage to roughly 0.6 V and then decreases to 0.2 V before Closed-Loop is enabled.

What causes this behavior? Heat and/or the open-loop AFR over time (getting leaner)?

On my nephew's car, the NBO2 sensor stays around 0.5 v all of the time. If I decrease the fuel pressure, the NBO2 voltage falls. Although the response time is slow.

He is running Edelbrock TES headers with the Tri-Tech coating. I wonder if we are running into NBO2 heat issues?

I had not seen these problems with Jet-Hot coated headers.

Thanks in advance for any help that my be provided.

Best Regards,

Bruce Wilcox

 

A single wire O2 with headers can sometimes cause it to stay too cool for closed loop operation. Installing a 3 or 4 wire heated sensor usually cures this little problem. For closed loop to be enabled, there are several timers. One is coolant temp, another is the all important O2 sensor temp. The ECM waits a set amount of seconds before it starts to listen to the O2 sensor. If the sensor is not hot enough, it will never tell the ECM that its ready for closed loop. I would start by first checking your coolant temp sensor then if it tests good, look into installing a heated O2 especially with headers.

 

Hi,

Thank you for the comments.

The coolant temperature sensor is new and the data from TunerPro indicates that the correct temperature is being reported by the ECU.

One other potential problem is the injectors. I believe that they are made by Accel. Not sure about the quality?

Based on my nose, the car smells rich at idle.

Is it possible that more than one problem exists?

Best Regards,

Bruce

 

Dump those Accel injectors and get yourself some ford injectors. The Mustang #19 pounders will work wonders on it. Also if your CTS is reporting the correct temps then install a heated O2 sensor. I think your O2 is not staying at the proper temp and the ECM is not entering closed loop because of this.