402 running lean at idle
402 running lean at idle My condition seems a little different than most that I have seen. The car had been running 14.7 at idle via my LM1 wide band. Now it seems that all of a sudden when the car goes into closed loop I am idling around 16.5-17.0 AFR. Nothing has really changed on the car at all. I know my VE table is right because the LTFT at idle is about -6/-8 and if I clear the fuel trims with the car running the AFR goes to 14.7 then the fuel trims bring it back to 16-17.
If I drive the car it holds 14.7, when I come to a stop it will idle at 14.7 for a little bit then go back to 16-17. I was thinking it could be my long tube headers, no cats, not holding in enough heat. The weather is cooling off so maybe that is affecting it. My map reading has also stayed the same, the car idles around 68-69 KPA, 900 RPM, 15 degrees advance at idle. So, I am thinking I do not have a vacuum leak. I have a log that I can post later, just looking for some ideas.
If I drive the car it holds 14.7, when I come to a stop it will idle at 14.7 for a little bit then go back to 16-17. I was thinking it could be my long tube headers, no cats, not holding in enough heat. The weather is cooling off so maybe that is affecting it. My map reading has also stayed the same, the car idles around 68-69 KPA, 900 RPM, 15 degrees advance at idle. So, I am thinking I do not have a vacuum leak. I have a log that I can post later, just looking for some ideas.
If your trims are -6 and -8 you could dial in the ve table a little better although thats not the problem. I shoot for +-3 when Im tuning something. Depending on cam size and how far back your O2's are they make it think its lean at idle. How you tried turning off ltft's and log just stft's to see what they are doing at idle? You may have to adjust O2's at idle so they are not leaning it out so much. Have you tried any more timing, 15 on a big cam may be alittle low.
If your trims are -6 and -8 you could dial in the ve table a little better although thats not the problem. I shoot for +-3 when Im tuning something. Depending on cam size and how far back your O2's are they make it think its lean at idle. How you tried turning off ltft's and log just stft's to see what they are doing at idle? You may have to adjust O2's at idle so they are not leaning it out so much. Have you tried any more timing, 15 on a big cam may be alittle low.
I have thought about turning the LTFT's off but have not done it yet. Cam has 20 degrees of overlap, 02's are right in the header collectors. TSP 1/78". I have had the timing pretty well all over the place. The problem is that my IAC counts get to low with the timing up to high. I was running 17 most of the time but brought it down to 15. I think my VE would be close if the car was not trying to lean itself out and keep idle AFR at 16-17. If it were keeping it at 14.7, it would not pull as much fuel, fuel trims would be closer to zero with the VE I have now.
Thats how it used to be until this started showing up.
Cam has 20 degrees of overlap, 02's are right in the header collectors.
Its funny that you ask that because I did switch back to my stock IAT sensor. I had planned on going MAP only and getting rid of my LS7 MAF that has the IAT built in. I may plug the LS7 IAT sensor back in and see if it helps the problem. I did not get a chance to look at my log or post it up last night.
Looks like it was the IAT causing the problem. The LS7 sensor is a way better design because it is directly in the air path into the engine. The stock sensor was getting heat soaked and causing the AFR to lean out. I was getting a 120*F reading at idle there is no way the air coming in is that hot. So I will be hooking the LS7 back up.
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Joined: Apr 2008
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From: Dickinson, Tx
Personally I would use a breakout harness with a Omega sensor and get the IAT sensor away from the MAF. Some stick the IAT somewhere by the front bumper but where there's steady air flow when driving. Others put it somewhere by the filter.
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this is exactly what i did made the wires longer and located it away from the radiator and heat from the engine bay.
It seemed to be working fine running the sensor in the LS7 MAF. At least that way you are reading the exact air temp coming into the motor. The card style MAF hangs out directly in the path of the air flow. The design of it also keeps it from getting heat soaked.
