Fuel Trim Malfunction, should be fixed but isn't

[carcrazy144]

ok, other day was driving home from school, cel came on. Got it pulled from advance, fuel trim malfunction bank 1. Started the car to go home and it went away. Next day it came back and has been on for the past 2-3 days. I replaced the front o2 sensor since that is what commonly causes this cel but i still have the cel. I was wandering if the computer needs a couple miles put on it after a new 02 sensor to reset the cel. I know i don't have any vacuum leaks because that would cause my boost gauge to show less vacuum when at idle or decelerating. I do have a hairline crack in my exhaust manifold but from what i read, a hairline crack wouldn't be enough of a leak to cause a cel, and i know the gaskets before the 02 sensor are all good because i have a fairly new turbo put on in late december early january of this past year, also because of that i shouldn't have any cracks on the exhaust housing of the turbo (hot side).

So could my ecu just simply need to be reset by driving a few miles w/ a new 02 sensor or is there something else i should check? I also do know its running real rich because it blow black smoke when i get on it and the 02 sensor i pulled was covered in soot. That is another sign that the 02 sensor went but since i replaced it, shouldn't the cel have gone away?

Mike

 

[knochgoon24]

Have you reset the CEL after installing the new o2 sensor? It won't go away by just installing a new sensor.

You can reset the ECU and clear the CEL by disconnecting the battery for about a minute.

 

[carcrazy144]

No, i didn't, ill try that to see if that works.

silly me, should have known to do that, duh. Thanks for the quick response that was it.

 

[the_mork]

I know i don't have any vacuum leaks because that would cause my boost gauge to show less vacuum when at idle or decelerating.

FWIW this is patently untrue and entirely a misconception. When I blow off an IC pipe completely I see approximately the same vacuum as when my system is completely leak free.

A better metric is what your maximum boost is if you are using a manual boost controller or static duty cycle on an electronic boost controller. Even this isn't in any way accurate though because of atmospheric changes.

Further, while I may be able to spot a decent sized boost leak through logging my MAP sensor I guarantee that eyeballing a gauge isn't going to be nearly accurate enough.

Related to your problem or not do a boost leak test because it is the only way to know.