Thread: Car leaning out when ECTs rise

88mm VE, 12.5:1 compression, N1 cams, Xcessive Plenum /w Q45 TB, GM 1 Bar MAP, GM IAT, Nismotronic.

I am having a few issues I have been chasing since I got the car running this year. The biggest one right now is my AFR, at least at idle, is changing drastically as ECT rises. After a cold start, the car will idle at 14.7-15 AFR with ECTs from 155-160*F. After my drive to work, ECTs at 170-175*F, it was idling at 17 AFR. My ECT enrichment table goes to 0 at 158*F. My IAT sensor is in the plenum, and are staying in the 85*F range. Any ideas on what I can adjust to fix this? Do I need to add fuel the ECT enrichment table? Is there something mechanically wrong that would cause this issue? Car runs and idles great when temps are lower, it gets all crazy when temps rise and it leans out. If I can fix the leaning issue I think it will solve my other issues.

If needed I can grab a log tonight on my way home.

I think this is open to some discussion as idle issues are always a problem with SR's. But, I have always tuned the fuel maps to 14.7, and then all other trims to it.

John sent me a new tcd to try. I was so frustrated about this over the weekend I forgot I sent that to him. I will give it a shot and report back, maybe it could help others having the same issue.

Thanks John

Try adding some fuel in the

Fuel Trims > Fuel Adjust > ECT Corrections > ECT Enrichment tables.

I choose to idle at 15.3 AFR.

Also how much fuel is your o2 sensor trimming? If you o2 fuel trims are maxed out and if your issue is only at idle you may want to increase the amount of trimming your closed loop may do. You can find this in

Closed Loop > Closed Loop > Params > Fuel Trims

Running open loop at the moment.

John sent over a new TCD and it is better. Drivability is much better, but now it is moving more rich when ECTs rise but not nearly as much. Total fuel table is getting better so I will see if it gets better. It still has a jumpy idle after a warm start for 30 seconds or so.

The start issue is likely your initial closed idle valve duty vs ECT table.

Most of these bigger injectors will idle a little smooth at/around 14.0-13.5 and that might be what you want to target to get a smoother more consistent idle.

The thought came up that it is related to starting, since driving is fine. I will try adjusting that table and go from there. Thanks again for your help.

An exhaust leak that opens up as the temperature rises could cause lean AFR readings.

As always you were correct. Changed the Initial Idle Duty down to 10 when warm and it starts just fine.

Question: Does the post start high RPM spike do anything beneficial for the motor? If not I may reduce the Idle duty all over so there is not much of a spike after start at any temp.



The header may not be sealed but I am not sure, I tried my best to seal it. I am working on a permanent solution.

post high rpm spike is beneficial when its cold. without it, the car will sputter to a stop unless you modulate the throttle manually for a second or 2 to keep it idling while still pretty cold.