Fuel trim problems

Hey guys, my name's Steve I'm new to the forum and to the Scooby world. I just bought a completely stock 08 LGT spec-b with just over 74k on it. I have a couple problems I've been trying to sort out on it.

 

My main problem is my fuel trims right now. My stft usually fluctuates between 1.6-4.3 but sometimes it just starts climbing for no apparent reason my ltft is settled in @ 14.1 right now. I've smoke tested it several times, I had a leak between the IC-TB and fixed that now I've got no more leaks but my fuel trims are still jacked. I tried cleaning the mass air element and replaced the o-ring, any ideas?

 

I work at a shop so I was thinking of doing a fuel stystem treatment and disabling the EGR. Where is the EGR valve? Alldata gives me NODATA.

There is no EGR valve. EGR is accomplished by manipulating avcs.

As for the trims, learning A seems to fluctuate a lot but 14 sounds too high. Perhaps your manifold to the o-rigs need replacing.

Also, are you using the stock air box along with the resonator and a paper filter?

everything is stock, smoke test shows know indication of any other leaks. what really baffles me is the inconsistency sometimes it's 10.9 I can drive for the weekend check it again and it'll be 20.1

I did pull the resonator out of the bottom of the air-box, I can put it back in tomorrow if you think that might be an issue

Are you using learningview or just a regular obd reader to verify trims?

Using a snap-on solus. Re-installed the resonator, drove it @ 10 miles, re-checked fuel trims. Long term at 15.6

Other related problems I noticed are occasional really long cranking before start up, I have a slight stumble at idle that becomes really pronounced if you hold it @1800, and I definately have the misfire on hard acceleration between 3-4k rpm. Should I start with the TSB for the software update before I go nuckin futz trying to figure out why I'm seeing a lean condition?

bump!

Thanks for the input, I replaced my front air/fuel sensor and my stft is @ 0 ltft is 1.6. Unfortunately after replacing the air/fuel sensor and the plugs (I think I'd rather do them on a lifted 5.4 3v) I still have a slight stumble at idle and hard acceleration... Back to the drawing board

So what happened with this car mines seems to be doing the same thing and I leak tested all my hoses found a a leak ptft still higher than expected

My fuel trims in learningview are all at -15 my tuner says ther is apparent leak somewhere.. Idk much about fuel trims but isn't it read from the 02 sensor? If so could it be from runnin catless dp?

Maybe he's got a bad injector.

dont know anything about it just tryn to get my car tuned and he can't do it till these numbers are fixed

Holy crap that's ugly! Interesting you have a code for rear O2 too lean while the fuel trims are basically pegged as lean as they can go.

 

I was working on a WRX this week that was at -14 in A ramping up to -10 in C. A replacement MAF sensor sorted that but the second guess was the O2 sensor.

this is what i got after switching back to the factory tmic still doesnt seem right wouldnt aftermarket parts throw off the ecu without a tune?? also fahr_side said possibly maf sensor or mayb O2 should i look into those? wouldnt they throw codes if they were bad? i dont know alot about this but my brother is ase mechanic seems to think the O2 readings are off cuz of a catless dp..idk he stays pretty busy i hate to keep bugging him with this.. thanx everyone for the help still new here idk how to start a new thread

No, an intercooler isn't going to affect fueling in the absence of leaks.

So it's obvious Thers an air leak somewhere? I don't understand whats goin on here the pics are hard to see but the stock tmic brought the numbers up from -15 to -5 on 3 boxes 4th on is still -14.. I'm starting to get the grasp of the top box in lv but what is the bigger one on the bottom labeled knock correction? What are tear numbers supposed to be at.. The tuner says the ecu is dumping fuel tryn to keep from running rich? Is -15 not lean??? Also 1 question I can't find an answer from anyone is do aftermarket parts not throw of the ecu? The fuel trim is read from the 02 sensor which the o2 sensor is throwing codes for no cat makes since why the o2 readings would be off..anyway so if I can cancel the fmic and exhaust system from my checklist what else can I look into? Whats wrong with my car this is so frustrating shouldv seen the hassle I had getting lv to even read with the vagcom

The lower table, labeled knock correction, is areas in the ECU map (RPM vs engine load) where the ECU has learned there is consistent knock, and has pulled timing to pre-emptively compensate. Numbers in the higher column (for engine load) is concerning. Low-load knock is highly debated, but usually not a big issue.

 

Your fuel trims are still showing you're running rich. Fuel trims show how the ECU is compensating to hit AFR targets. Negative numbers mean you are running rich, and the car is removing fuel to try to compensate. Large numbers for column D are also issues, as this is usually open loop fueling (read: the ECU is guessing the right amount of fuel - there is not closed-loop feedback from the O2 sensor). Get a leak test done. That should help get some idea of what you are dealing with.

Also, if you are running a higher-flowing down pipe and have no tuned for it, proceed with caution, and stay out of the boost.

WOW....did you guys threadjack this one or what?

The ECU believes, correctly or not, that the AFR in closed loop is richer than it has targeted. To correct this it is reducing injector pulse width via the four fuel trims A thru D. If you had an air leak you'd expect the reverse happening.

 

As it is the system is trending almost to limit where you'll throw a code for system too lean. Remember it takes a little time for the trims to settle to a final value and it only gets adjusted while operating in that load range.

 

The few times I've seen this the following problems were found:

 

1. Failing MAF sensor giving a high reading, misleading the ECU to believe more air is flowing than is the case, leading to rich condition.

 

2. Faulty O2 sensor reads richer than real AFR.

 

3. Dirty or failing fuel injector(s) which stick slightly open and don't control fuel flow properly.

 

The fact that you have a trouble code for rear O2 too lean makes me question the front O2 sensor, which provides feedback for fueling that the trims derive from. The front O2 is saying the fueling is too rich across the board and the trims are a result of that. Somehow, the rear O2 disagrees.

Note that the trim value in range D is applied to open loop fueling. Normally a rich mixture helps control knock. The fact that you have IAM at <1 leads me to think you are actually running lean in open loop and knocking, which causes IAM to drop.

 

I would swap the front O2 sensor with a known good part as a first step.