Fuel trims at 10% or higher
11-17-2007, 09:56 PM
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Fuel trims at 10% or higher I have the Diablosport Predator that has some diagnostic abilities to it and I was checking out the car on the highway today. I noticed the long term fuel trims were pretty much sitting around 9.5 to 12.5 % which seems kind of high. I have the ported TB, a lid, the airbox mod and cut the EGR tube and it looks like it has helped airflow a lot. Is there a fuel trim range that means it's time for a tune like 15% or 20? The O2's were reading around high 700's most of the time on the highway as well. The car has the stock tune right now as far as I kknow. I plan on putting headers on shortly so I don't want to think about a tune yet.
11-17-2007, 10:39 PM
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You should be able to richen up the mixture (part throttle and WOT) with your handheld.
What concerns me about your statement though is you say the O2's were reading high 700's. Is that the mV's you see at WOT? If so, you're running pretty lean. If it's just driving around normal, they should be fluctuating between 100~700mV.
What concerns me about your statement though is you say the O2's were reading high 700's. Is that the mV's you see at WOT? If so, you're running pretty lean. If it's just driving around normal, they should be fluctuating between 100~700mV.
11-18-2007, 11:53 AM
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Sorry, I meant they were maxxing around high 700's. They go back and forth from 50 - 800 roughly during cruising if I remember. My handheld is VIN locked so I can't do anything with it right now.
11-18-2007, 12:33 PM
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But, the fuel trims seem a little high. You'll want to look into getting that handheld unlocked so you can adjust the fueling. Getting yourself setup with a WBO2 would be wise as well.
12-14-2007, 06:30 PM
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Well, I put on some longtube headers with dual 3" cats and y-pipe and I'm seeing 12 to 13.25% on the long term fuel trims now while cruising around 70 mph. Seems like my engine is getting air in and out really well and needs more fuel now. I haven't had a chance to check the WOT readings because it keeps raining/snowing/sleeting around here so there haven't been many chances to test it out. I'll most likely get a tune but I guess I need to decide when to stop doing mods to get it. 
12-15-2007, 01:24 PM
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Keep in mind that when you run a positive fuel trim--the ECM will lock on a positive fuel trim that it sees just BEFORE going into PE or WOT--So you are adding that 9.5 to 12.5 fuel to your WOT fuel curve---If you have a stock tune it's somewhere around 11.5 at WOT and you are adding 12.5% to that--very rich !!! However if the ECM sees a negative fuel trim just BEFORE going into PE--it will always lock on "0"---That's why its always better to shoot for a "0" or slightly negative trim so that you aren't adding any aditional fuel at WOT---
So, in his case, the fact that his fueling is off that much at cruise is ever more of a reason to get his hands on a WBO2....because there's that much more fueling variation happening at WOT.
