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05-01-2017, 07:57 AM | #1 |
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Z4M- Long term fuel trims-thoughts and ideas please
I recently downloaded and had a play with the OBD Fusion app (great app btw) and noticed my long term fuel trims were strangely high (-17%). From what I can gather this would mean the car thinks it's running rich and cutting (a lot) of fuel.
The car is running alpha-n and an evolve airbox and was all fitted about 18months ago and seems to drive fine but obviously I'm concerned at these trims. No codes are stored, no real driveability issues but I'd like to get to the bottom of it-any thoughts as to what might be the culprit or what I should do? -perhaps there's a combination of PIDs I can log to give me a clearer picture? This whole data logging and diagnostic work is very new to me so any help and advice would be greatly appreciated! Thanks in advance |
05-04-2017, 06:17 AM | #2 |
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Drives: ESS/G-Power Z4M, VF Z4, 996tt
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Outside of programming the ECU to eliminate hardware errors for running MAF-less, and WOT spark advance / AFR / VANOS / etc., I suspect the tune has been altered in two areas:
1. The ECU has a transfer function for the intake, which should be adjusted any time the intake/sensors are modified. 2. Transient fuel tables, taking into account the advantages provided by the new intake setup. You can try resetting the fuel trims, and watching your STFT on light load, then abruptly moving to WOT. Odd STFT with constant light load would indicate the alpha-n tune hasn't accurately accounted for the airbox (intake transfer function needs to be modified). If constant part throttle is good, but abrupt changes in throttle result in a high STFT, the transient throttle fuel maps need to be adjusted (tweaking these tables should only occur after confirming the intake transfer function is accurate). A dyno tune is the ideal solution for either scenario, assuming your O2 sensors are giving accurate feedback. If they are old, I would replace them first to avoid spending big $$ on a tune when it's a sensor issue.
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05-04-2017, 01:11 PM | #3 |
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Thanks pokey, I appreciate the input
I'll have another play with it this weekend and try to monitor the stft's. As far as I know the O2 sensors are original so may be worth swapping those-is there any reliable way to test them before shelling out? As for resetting the fuel trims, unfortunately I have no way to do this at the moment. The app I use doesn't cater for this and I have no laptop either. Any thoughts on Ho to go about it? |
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06-18-2017, 05:44 PM | #4 |
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Sorry for not updating sooner but I've been snowed under with work and forgot about this thread.
I've had a little play with the app again and it turns out to be a little different than first thought. I'm not entirely familiar with it all yet so I'll leave any final conclusions but I'm fairly confident that it was more down to my mis-interpretation rather than a serious issue. The Cayman R I 'met' on the way back from my logging trip would no doubt confirm that the car certainly goes well enough! I'll continue to play about with it for a while as it's quite a nice thing to fiddle about with but ultimately I'd like to get the car back to the dyno and have a proper custom map made for it as well as getting some expert opinions on the current state of affairs. |
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06-20-2017, 06:35 PM | #5 |
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No doubt, I gotta also add, if your using generic software to monitor events and sensors be carefull. I had myself in all sorts of worry when I was using Android software to monitor some of the elm outputs in my 2013 JKU. Turns out the numbers were incorrect due to non alignment and calibration of software. Lol I can laugh about it now.. make sure your using the right software/hardware.
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06-27-2017, 04:57 PM | #6 |
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Yeah, that's a good point-it's a generic program for all cars as far as I can tell and like your stuff, seems to just relay the data from the OBD reader. In theory it 'should' be correct but who knows? I've no way to actually test and verify it sadly.
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