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Old 08-14-2011, 08:48 AM   #22
Cobb Tuning
Member#: 4803
Join Date: Mar 2001
Location: Austin, TX

Originally Posted by mightymints View Post
Bill, I went to a car meet tonight and due to it being busy on the roads, the best pull at WOT I could get was the following:

But I will get you a 2500 to redline tomorrow.

At the meet, various people checked over my car and said that it sounds fine, and one of the guys is going to help me do some pressure testing this week which is sweet.

Just so I understand a little more, how can you tell that it is pulling 11% of fuel from those tables?

Thanks again, I definitely owe you some beers!
In your previous logs, A/F Learning 1 (your long-term fuel trims) has touched on -10% and -11%. There are 4 different A/F Learning 1 values (A,B,C,D) that can change at any time based on patterns of your short-term fuel trims (A/F Correction 1). When you log A/F Learning 1, it is showing you the current applied learning (the 4 are stored and applied across 4 different mass airflow ranges).

Generally, A/F Learning should stay somewhere around +/- 5%. When you start seeing double digits, it can indicate a potential fueling-related problem:
1. Aftermarket injectors and/or intake used and not tuned properly in the map (does not apply to you if your car is all stock besides a catback and you are using our stage 1 OTS maps).

2. Post-MAF sensor, pre-front o2 intake/boost leak - Air that has already been metered is being lost (go rich) or air is being introduced into the system that has not metered (go lean).

3. Bad MAF sensor - ECU calculates airflow and therefore load and fueling based on MAF sensor, so if airflow is different than actual because of bad MAF sensor, fueling will be off and, in closed loop, the ECU will attempt to correct this via front o2 feedback (which you will see as more extreme short-term and long-term fuel trims).

4. Bad front o2 - ECU uses front o2 for feedback in closed loop. If that feedback is wrong, the ECU will be making the incorrect corrections causing fuel to be off in closed loop (and possibly in open loop via "D" range A/F Learning 1).

5. Some other mechanical issue - leaky injector, fuel pressure issues, etc.

You can't necessarily hear an intake leak (nor find it visually), so it is good that you are getting a pressure test done.

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Last edited by Cobb Tuning; 08-14-2011 at 11:01 AM.
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