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Thread: running lean

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Posts: 11-13 of 13
2008-05-04 16:27:08
ok so ive changed the chip for the ecu to an extra one that i got and its the same thing. pressure checks show that fuel pressure is good... checked the value on ma tps and closed its .45 and at wide open throttle its 3.8, was told that it should be at 4.5.... could this be the cause??? i will be swapping the regulator on the rail to make sure that its working too..... still need some assistance here
2008-05-05 00:35:43
I heard that if you test the afr after the cat that it will apear to be lean. I dont know how true that is though.
2008-05-08 16:25:35
Pre-cat and post cat readings are so close at wot that its a moot point. The cat, due to its chemical nature, stores oxygen to some dgree, when you transition to wot you get a "false" lean reading caused by the oxygen getting evacuated by the incomeing exhaust. However, once the exhaust colum is moving, (half a second ofter wot at the most) the 02 readings stabilize and you get a very accurate reading bareing exhaust leaks and the like. I have run many tests with 2 o2 sensors, one post and one pre cat on the same run and compared afr. Other than the already mentioned lean bump at transition, both readings are within .1 afr point. Concidering your injectors, and your runner flow varies by much more than this, post or precat is not going to cause you any issues.
Make sure your fuel pressure stays constant under load, Just because it looks good at idle does not meen sufficiant fuel flow at wot. Obviousky fuel demands at idle are alot less that wot.
What is the afr at idle? Is your pcm setup for open or closed loop? If open loop idle afr will help you determine your issue. If closed loop, the learned correction will help you determine the problem. What is your cruise afr? Is the car lean everywhere or just wot? Make sure the maf is clean, a log of the wot run with maf voltage can help you determine this. In any event, a fpr will help you sort out your afr issues.
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