General 140% Low Fuel Trim, bad milage, lurching?

[Zenja]

I have a feeling all of these are co-related. My low fuel trim is 140%, mid is 120%, high is 108%. I get about 16mpg in the city and my car lurches quite a lot when I give it gas from an idle cruise, especially in first gear.

My best guess on the fuel trims is a vacuum leak which could cause all the other problems as well. However, it seems like I might be running lean at WOT because I get some knock (granted this was on 90 octane gas but stock boost). I was also thinking my occassional phantom knock might cause problems.

Here's TMO logs, they might be relevant:
http://zenja.no-ip.com/logs/TMOlog1.tlg
http://zenja.no-ip.com/logs/TMOlog3.tlg

 

[kpt4321]

Pressure test the car.

Also, is it possible that you have a dead O2 sensor?

 

[Zenja]

I want to pressure test it as it seems like a vacuum leak is the most likely cause. I've checked all the hoses by sight and listening while the engine is running so many times though. Under vacuum if there's a hole where unmetered air can come through then that would cause the car to need to add more fuel hence the fuel trims. On light throttle where little airflow is needed and where there's the most vacuum that's where it seems like the percentage of unmetered air could be the greatest. My airflow hz is only like 28 at idle with 7% throttle.

By the logs my O2 sensor seems good but I've been thinking about replacing it anyway.

 

[Erok]

its late and im alil drunk, but like you were saying how from a regular cruise, then when you wot it it lurches, i dont think that is vac, cause as soon as you wot it it sends the ecu into a open/closed loop, cant remember which what it is, think it goes closed at wot, but when in the kind of look it blocks off your vacume as sloot as boost builds at wot, it least i think thats how it works, just ask some people some questions about my post might be able to better explain it.(+ im drunk)

 

[psychlow]

Open loop at WOT, meaning it stops caring about the oxygen sensor readings.

 

[Zenja]

It doesn't have to be WOT. With no gas in 1st gear going really slowly, even a little bit of gas makes it lurch a lot for like two seconds.

 

[2.4 turbo Hyped]

You and I might be having the same problem. Turn on your ac and see if your low fuel trim corrects itself ( goes back to 100-110%). This is what my car is doing right now. I can be idling with the engine warm and the low trim is maxed out lean at 138% (mmcd) and the fto2 is at 167.8% but as soon as I turn the ac on the low trim will trim itself up to where it should be at 110-100%. Let me know if you can replicate this problem and we will figure out what the issue is. Regards, Sean

 

[Bohrn]

What kpt4321 said. to quote Hutch, "Do it" "do it"

high fuel trim numbers mean leaner mixtures, so if your O2 sensor is good(the trims are based on its feedback) then you must have a leak.

btw, leaking at idle is quite a bit different than leaking under pressure. It might be good for 10 psi even, but once it hits 12 or whatever magic number, then it will leak counted air. Then ECU thinks it has that air, so it injects that much fuel. But when that air doesnt show up, its way too rich.

 

[2.4 turbo Hyped]

No leaks. Holds 20 psi nothing short of perfect. Like I said before the low fuel trims will act normal when the ac is on but when I turn it off the low trim shows way lean. Has to be some sort of a sensor causing this crap.