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      12-19-2011, 05:35 PM   #1
GeorgiaTech335coupe
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What can cause fuel trims to not work sometimes?

This has happened a couple times while I have been logging. For some reason my fuel trim for one of the banks is at 0, causing my car to run very lean while WOT. Then instantly, the car will recover and fix the fuel trim. See log posted below. This was on a 3rd-4th gear pull. I have also seen this happen at the dragstrip. It happens sporadically, most of the time its fine though. I had some dragstrip passes the same night as the log below and they looked fine. What are your thoughts?
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      12-19-2011, 05:35 PM   #2
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o2 sensor on the way out? Any codes?
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      12-19-2011, 05:37 PM   #3
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No codes. Why would it be an 02 sensor? The AFR readings seem fine. If the O2 was bad and it was giving false lean readings, wouldn't that make the fuel trim max out? The car is reading lean, but no closed loop fueling is occuring to correct it.
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      12-19-2011, 06:21 PM   #4
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The Procede readings are calculated, not actual lambda. Try upgrading firmware and resetting everything in the Procede and ECU. I'd start with electronics bug first, then look for bad O2 sensor (turn off CAN clear) and other sources of bad lambda on one bank only. Could also be a bad connector pin or something shifting in the ECU box causing a weird O2 signal intercept in the harness.
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      12-19-2011, 06:27 PM   #5
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Quote:
Originally Posted by GeorgiaTech335coupe View Post
No codes. Why would it be an 02 sensor? The AFR readings seem fine. If the O2 was bad and it was giving false lean readings, wouldn't that make the fuel trim max out? The car is reading lean, but no closed loop fueling is occuring to correct it.
I dont know if its an o2 sensor. However, fuel trims and AFR all feed from the o2 sensor. Although as you know with piggybacks the AFR is calculated based on its own algorithm.

In a traditional sense, fuel trims are based on what percentage of fuel is needed or taken away to meet target air fuel. The target air fuel is built into the DME and short term fuel trims are calculated from the o2 sensor.

There may be some sort of corruption as James mentioned above. I would look into a full reset, adaptations, and reupload of firmware and maps.

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      12-19-2011, 09:40 PM   #6
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At one point i was getting 0 trims after a shift, but i was too rich. Zero trim is supposedly open loop mapping only. It does happen during a shift for a brief time (at least in my logs).

I would try bumping up the OL mapping trying to get trims <20%.
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      12-30-2011, 05:31 AM   #7
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Did you fix your problem? On my recent dyno, Bank 2 Fuel Trim maxed out on every runs, I did reupload map/firmware as soon as I got home but havent had a chance to drive the car yet.
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      12-30-2011, 11:20 AM   #8
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Quote:
Originally Posted by creaminz View Post
Did you fix your problem? On my recent dyno, Bank 2 Fuel Trim maxed out on every runs, I did reupload map/firmware as soon as I got home but havent had a chance to drive the car yet.
I haven't really had time to do anything with my car lately. I plan on loading the new maps/firmware. Maybe it was corrupt, but honestly I doubt that was the situation.

What date maps were you running? I know that maps newer than 11-1 have more fuel on the open loop fueling. This is for stage 3 which I am as well. IF you were running 11-1 stage 3 then that is probably why. At the strip running 11-1, I had to adjust my open loop to 100% and I would still see positive fuel trims during the run (not maxed at 34, but still in the teens). I'm assuming with the newer maps, will fix this so that the standard 90% will be a lot closer to 0% fuel trim.

My problem was different than what you were seeing. I would see 0 fuel trim on one bank, and a big positive # in the other. The AFR in the 0 fuel trim bank would by scary high, while the other would be perfect. Then halfway through the gear it would correct itself and both would look perfect.
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      12-30-2011, 03:06 PM   #9
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Oh wow your situation seems alot more complicated than mine. Yes I am running 11-1, maybe I should load up 11-25 map/firmware to see what happens.
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      12-30-2011, 03:37 PM   #10
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Quote:
Originally Posted by GeorgiaTech335coupe View Post
I haven't really had time to do anything with my car lately. I plan on loading the new maps/firmware. Maybe it was corrupt, but honestly I doubt that was the situation.

What date maps were you running? I know that maps newer than 11-1 have more fuel on the open loop fueling. This is for stage 3 which I am as well. IF you were running 11-1 stage 3 then that is probably why. At the strip running 11-1, I had to adjust my open loop to 100% and I would still see positive fuel trims during the run (not maxed at 34, but still in the teens). I'm assuming with the newer maps, will fix this so that the standard 90% will be a lot closer to 0% fuel trim.

My problem was different than what you were seeing. I would see 0 fuel trim on one bank, and a big positive # in the other. The AFR in the 0 fuel trim bank would by scary high, while the other would be perfect. Then halfway through the gear it would correct itself and both would look perfect.
There's a lot of misconceptions regarding fuel trims going around...mostly thinking any 'trim' is necessarily bad. When you see the fuel trims are under 34 (max), then you are perfectly fine to drive about; no fuel tuning required. It's only when fuel trim(s) are fully maxed out that adjustment can be beneficial. FWIW, I think there are only a handful of FBO cars, myself included to actually and routinely max out fuel trims on pump-only maps. In my case, I think it has to do with the ethanol content in the winter fuel up here. In any case, 'normal' cars should be well within the ranges unless something else is going on.

Georgia Tech and Creaminz- your situations are definitley much more than just adjusting fuel trims; there is something fierce goin on in the background.

Creaminz- did you ever get your O2 sensors checked out to see if they're flip flopped?
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      12-30-2011, 03:42 PM   #11
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Injectors would cause that.
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      12-30-2011, 04:40 PM   #12
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BrianMN,
I checked my O2 sensors and they are plugged in correctly. I have replaced valve gasket and also did some intake valve cleaning, about to drive the car out to see what happens now. Prolly upload 11-25 map before I test drive.
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      12-30-2011, 04:45 PM   #13
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      12-30-2011, 04:51 PM   #14
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Right, but you've gotta trace them wires back to the connectors to make sure that they're the correct O2 sensors for the correct bank....also do the same for the rear O2 sensors. When I get home I'll look to see what color wire sleeve goes to which bank; although I'm sure the info is somewhere in here.
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      12-30-2011, 05:01 PM   #15
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Quote:
Originally Posted by BrianMN View Post
There's a lot of misconceptions regarding fuel trims going around...mostly thinking any 'trim' is necessarily bad. When you see the fuel trims are under 34 (max), then you are perfectly fine to drive about; no fuel tuning required. It's only when fuel trim(s) are fully maxed out that adjustment can be beneficial. FWIW, I think there are only a handful of FBO cars, myself included to actually and routinely max out fuel trims on pump-only maps. In my case, I think it has to do with the ethanol content in the winter fuel up here. In any case, 'normal' cars should be well within the ranges unless something else is going on.

Georgia Tech and Creaminz- your situations are definitley much more than just adjusting fuel trims; there is something fierce goin on in the background.

Creaminz- did you ever get your O2 sensors checked out to see if they're flip flopped?
Exactly. Anything under max fuel trim is safe, but closer to 0 during WOT the better as the car has more ability to correct itself if something bad were to happen (like my situation for instance were one fuel trim 'doesn't work'.) If I could get the open loop to a point where fuel trim was very close to 0 during WOT, then my problem wouldn't be as scary to me.

Another thing to consider is that fuel trim is what is needed to hit the AFR setpoint which can be anything. I believe Shiv is targeting a pretty rich AFR probably more than needed, so even if you max out fuel trim you probably are still hitting a safe AFR, just not the setpoint AFR.

I am not really sure what is causing this problem I am having. It only occurs sometimes so it's either a bug in the software or a flaky mechanical device. The way I see it, there is no reason why fuel trims in each bank should be drastically different, and I highly doubt anyone has ever seen a flatlined 0 fuel trim during a WOT pull through more than half the gear so I know there is a problem.

What I need to figure out is: What exactly influences fuel trims (input variables)? What exactly is the Procede showing me when it shows the -34 to 34% fuel trim (what is the input data that spits out the percent # and where is it collected)? What is used to calculate the AFR reading shown through the Procede, including variables into its algorithm and sensor data inputted?

Is the Procede AFR influenced by the fuel trim value or is it derived completely separately? Can the fuel trim value being shown by the Procede by a wrong and untrue value than what is occuring?
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      12-30-2011, 05:09 PM   #16
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Is the problem there when running stock?
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      12-30-2011, 05:22 PM   #17
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Quote:
Originally Posted by GeorgiaTech335coupe View Post
Exactly. Anything under max fuel trim is safe, but closer to 0 during WOT the better as the car has more ability to correct itself if something bad were to happen (like my situation for instance were one fuel trim 'doesn't work'.) If I could get the open loop to a point where fuel trim was very close to 0 during WOT, then my problem wouldn't be as scary to me.

Another thing to consider is that fuel trim is what is needed to hit the AFR setpoint which can be anything. I believe Shiv is targeting a pretty rich AFR probably more than needed, so even if you max out fuel trim you probably are still hitting a safe AFR, just not the setpoint AFR.

I am not really sure what is causing this problem I am having. It only occurs sometimes so it's either a bug in the software or a flaky mechanical device. The way I see it, there is no reason why fuel trims in each bank should be drastically different, and I highly doubt anyone has ever seen a flatlined 0 fuel trim during a WOT pull through more than half the gear so I know there is a problem.

What I need to figure out is: What exactly influences fuel trims (input variables)? What exactly is the Procede showing me when it shows the -34 to 34% fuel trim (what is the input data that spits out the percent # and where is it collected)? What is used to calculate the AFR reading shown through the Procede, including variables into its algorithm and sensor data inputted?

Is the Procede AFR influenced by the fuel trim value or is it derived completely separately? Can the fuel trim value being shown by the Procede by a wrong and untrue value than what is occuring?
Here's an even more strange scenario- A friend/employee of the shop I used to work at is having a very strange issue that is also throwing the following codes:

2C3D 11325 Lambda probe in front of catalytic converter, control failure
2c7e 11390 Lambda probe behind catalytic converter, trimming control
2C7F 11391 Lambda probe behind catalytic converter, trimming control

It appears to me that this person's issue is with the O2 sensors not working or something related to faulty exhaust readings; as the issue began when he started smelling rotten egg from the exhaust a week ago.

In the following pic: Fuel Trim and AFR from Bank 1 appear to be non-existent. This is even before the pull begins. Very strange.
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      12-30-2011, 06:06 PM   #18
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I had that 2C3D code years ago and it was fixed when I replaced the O2 sensor.

That is a very odd looking data log. It looks like the 02 may fix that issue. Maybe I should replace my O2 sensor, although I'm not fully convinced that is my issue and I hate throwing parts at the car to try and fix things.
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      12-30-2011, 07:39 PM   #19
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I had one experience with A/f. Did one run a couple of weeks ago and after I came to a stop the A/f was reading at idle 17-18 at idle. It normally goes back down to 14 but this time it never did. I shut the car off and turned it back on and the readings were normal again. I went home and reloaded the maps and firmware and I have not seen this strange occurrence again. I honestly think there are inherent bugs in the program which some variable will trigger it and odd. CouPle of months ago my cooling fan turned on while I was coming home from work. I just saw my fully warm engine oil drop from 240 down to 170 and I was like WTF. Pull over and heard the fan blasting away. Turned off car and turned it on again and fan was still running blast. I then went to procede reader and reset the ecu and the procede and then started the car. Back to normal. I went home and reloaded the maps again and haven't had this issue since summer. Very weird things. Your issue can be also bugs in software
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      12-31-2011, 12:12 AM   #20
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Quote:
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Front bank O2 sensor sheathing looks screwed up. That is where the sensor gets its air reference sample, and damaging the sheathing that close to the sensor body can screw up the sensor's operation.
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      12-31-2011, 01:11 AM   #21
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Car is still running lean & fuel trim maxed not sure if it's good idea to track my car tomorrow...
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      01-02-2012, 11:28 PM   #22
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Front bank O2 sensor sheathing looks screwed up. That is where the sensor gets its air reference sample, and damaging the sheathing that close to the sensor body can screw up the sensor's operation.
Thanks for your input, i will replace it to see if that fixes it...$250 for o2 sensor...damn!
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