Aragorn
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« on: November 23, 2011, 12:29:46 PM »
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Ok so i've been finding my way around the workings of the ME7 ECU's with the aim to build myself a basic stage 1 type tune for my engine (1.8T ME7.5) at some point.
To start with my aim would be to remove some DTC's for missing emissions equipment and to bring the boost upto around 1 bar.
The car is fitted with a hybrid turbo, so some tweaking of the Boost PID will also possibly be required to iron out any spikes/surges etc.
I've noticed some mention on some Audi forums of late, people discussing badly tuned engines, typically where someones baught a stage 1 type remap dirt cheap from someone and the map is a mess and/or baught an already remapped car and discovers its shonky when the car goes on the dyno. The comments often include mention (amongst other things) of the engine running dangerously lean at WOT because the tuner has simply "turned the boost up", and thats what i'd like to know more about.
Having read various materials on this site, i cant get my head round why the engine would run lean. The fuelling is based on MAF readings, boost is based on specified load. If i increase spec load (to say 170-180 as i plan to) surely the airflow increases, and the MAF sensor measures this and the ECU calculates and adds the appropriate amount of fuel for the now increased airflow.
So long as you dont run off the end of the MAF scaling, or run out of injector duty, which i cant see would be possible with a standard K03 turbo equipped car, how exactly do you end up with lean fuelling?
The fuelling changes i've found on these forums seem to refer to installing larger injectors, changing fuel pressure, fitting a larger MAF etc, ie all things that change the calibration between airflow, and injected fuel quantity.
Is there some other calibration i'm missing here? Some colleration between load and desired AFR that ends up incorrect or "off the scale" once the spec load and thus boost has been increased?
Hope someone can help!
Cheers
Kev
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Rick
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« Reply #1 on: November 23, 2011, 12:49:47 PM »
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You're essentially right, but one example would be an under scaled MAF and then not adjusting EGT model to suit. Loads would be artificially low, and there would be too little enrichment.
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Aragorn
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« Reply #2 on: November 23, 2011, 01:02:45 PM »
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But given a standard engine, with its original MAF, why would the maf scaling have been touched?
Its odd because i've heard the same thing mentioned a few times by different people, ofcourse they've all been the car owners relaying the info they've been told, and it may well have been oversimplified by the dyno operator or tuner plus the usual Chinese whispers effect by the time it actually gets onto a forum.
But it certainly had me worried about making the same mistake, hence asking the question!
Cheers
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julex
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« Reply #3 on: November 23, 2011, 01:43:09 PM »
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Well, you're talking ME 7.5 with wideband O2s that will correct AFR for you if your MAF is badly off. You can't easily (I believe) make it run lean unless you truly run over your injectors flow which in stock form is possible to do even with k03 turbos.
To run higher boost you'd also want to run lower AFR/Lambda which would add to the possible problems with injectors or fuel pump.
I am not sure what's the weak point of you car but I believe it would be the fuel pump as it is a returnless system?
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Aragorn
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« Reply #4 on: November 23, 2011, 02:22:37 PM »
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Thanks julex.
If the Wideband allows it to correct AFR, does that mean there is a Table which controls desired AFR vs load?
The car is a B5 A4, its currently on ME3.8, but i'm collecting the parts to convert it to ME7.5. As such it'll be on a standard fuel rail with return, and stock S4 fuel pump.
The injectors are ~310cc and the MAF apparently maxes out around 215g/sec which are both way beyond what the turbo can flow (circa 240hp).
I just cant work out why something that seems so simple can be messed up so badly by someone claiming to be a professional!
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Rick
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« Reply #5 on: November 23, 2011, 02:30:57 PM »
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There are maps for lambda vs load. On certain ECU's, at high loads this lambda simply isn't rich enough. On a std map i have open at the moment as an example, it only requests lambda 1 in the BTS at a load of 170 at 6500rpm. At a load of 150, which is around 0.8bar/std boost, lambda is down to 0.68 in the BTS, although this will be limited by the rich limit.
Rick
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Aragorn
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« Reply #6 on: November 23, 2011, 02:49:09 PM »
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Ahha, so reading this: http://s4wiki.com/wiki/Tuning#Desired_AFRI presume the tables we're talking about are KFLBTS_0_A and the others mentioned there? When i looked over that i took "EGT Enrichment" to imply the safety system that kicks in on an S4 when the EGT's exceed 950c, but looking again i can see it could feasibly come in much lower depending what TABGBTS is set to, and how the ECU models the EGT. I'm not sure what it means about LAMFA, it sounds like thats not really used by the standard ECU map? Cheers Kev |
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Rick
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« Reply #7 on: November 23, 2011, 02:54:26 PM »
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LAMFA isn't used as std no. The EGT info in wiki is nothing to do with EGT sensors - that's a totally seperate function.
Rick
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