What year is your car?
- You know for sure that the car used to not change AFR with time on track? I'm not sure what is typical. Difficult to tell from the screenshot, but perhaps 1 AFR richer by the end?
- Assuming NB, Have you plugged in an obd2 scan gauge to confirm the the ECM reported IAT and coolant temps are appropriate? I'd especially try to capture these values when your idle hang occurs.
- Ensure you don't have any exhaust leaks, could affect your wideband reading. Not sure why it would only leak later on in a session, though.
- What does the wideband read at idle when the ecm is controlling afr to stoich via the switching sensor? Anything other than 14.6 to 14.8 might indicate a wideband accuracy problem. How about when you come off the track with the car hot?
Thanks for the note !
-The car is a 99, built it over the last year. Only has 2 race weekends on it. New engine went in over the winter. Has done this every time it went to the track as far as I can tell. Before that no idea, it was a running street car I used to commute and drive around and it was not throwing any codes.
-Yes about 1.5 point leaner by the end of the race. The values for the position of the marker are in the columns on the left.
Car was set on a dino and was ending way lean during first race weekend. Re-set pressure after a session on the mobile dyno at the track during the last weekend, now starts the race way rich.
-Plugged my ODB2 scan and both IAT and Coolant temp look appropriate. Wasn't able to reproduce the idle hang, but it did have a code stored p0507 this time around. So replaced the air control valve with a cleaned spare and checked connection. Reset the idle. Code cleared now.
--> Does the ECU need a certain number if incidents over time to throw this type of code ? as in could the issue have started to cause a problem but the code only appear after a while ?
-As far as I can tell there are no exhaust leaks. But I'll go ahead and recheck and re-torque the manifold and down the line as well.
Both the primary o2 sensor and the wideband are in the down pipe, the primary in the stock location in the elbow right after the end of the exhaust manifold and the wideband 6-8" further back. Wouldn't an exhaust leak before that influence the primary as well and make the ECU go richer ? Although I imagine the Fuel pressure regulator effectively caps how rich the system is allowed to be.
- At idle the Wideband usually start around stoich for a while and then would eventually drift to leaner. I was told not to worry about idle readings so I did so, but since it continues during races over time I want to make sure I understand what is happening.
-Attached is a graph of the logged wideband with the car hot, left to cool down idling on the Dyno after 15min of pulls loaded trying to heat soak it to reproduce the issues.
Coolant temp (not on the graph) at the start is about 195 and goes down and stabilizes around160 mid way.
You can see the overall drift up (leaner) over time. Start around 14.7 and ends around 16. (for reference horizontal dashed line is 13, top one 20)
I condensed the graph to make it easier to see the drift over time and pay less attention to the extreme peaks.
Idle was between 850 and 900rpm.
I'll start it cold and let it completely heat up for a while see if it happens again now that the IAC has been replaced.