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PassatWorld Staff
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Discussion Starter #1
Voila!

You can monitor STFT (Short Term Fuel Trims) and Open Loop vs. Closed Loop operation with VAG-COM blocks 088 or 099 (they both give the same info):

STFT = Block 088, Field #3: O2 Sensor Control %
OL/CL = Block 088, Field #4: O2 Sensor Control Status
------------------------------------ O2 Reg.OFF = Open Loop
------------------------------------ O2 Reg.ON = Closed Loop

And as reported in a different post, Long Term Fuel Trims are block 032:

LTFT = Block 032, Field #2: O2 Sensor Learning Value @ Part. Load
 

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More on block 32...

Block 32 Field 1 = Additive fuel trim (most effect at idle)

Block 32 Field 2 = Multiplicative fuel trim (most effect at part/full open throttle)

^^^^^^^^^^^^^^^^^^^^

Block 32 Field 1 greater than +10%... too lean at idle: vacuum leak, clogged injectors, fuel line/pressure restriction

Block 32 Field 1 less than -10%... too rich at idle: dirty air filter, dirty TB, debris in intake

Block 32 Field 2 greater than +10%... too lean while accelerating: clogged injectors, bad MAF, fuel line/pressure restriction, hole in intake between MAF and turbo.

Block 32 Field 2 less than -10%... too rich while accelerating: boost leak, dirty air filter, dirty TB, debris in intake

^^^^^^^^^^^^^^^^^^

For those who don't know (like me)... What does open loop vs. closed loop tell us about our engine??
 

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Rusty said:
Voila!

You can monitor STFT (Short Term Fuel Trims) and Open Loop vs. Closed Loop operation with VAG-COM blocks 088 or 099 (they both give the same info):

STFT = Block 088, Field #3: O2 Sensor Control %
OL/CL = Block 088, Field #4: O2 Sensor Control Status
------------------------------------ O2 Reg.OFF = Open Loop
------------------------------------ O2 Reg.ON = Closed Loop

And as reported in a different post, Long Term Fuel Trims are block 032:

LTFT = Block 032, Field #2: O2 Sensor Learning Value @ Part. Load
good work 8)
 

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PassatWorld Staff
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Discussion Starter #4
pete1 said:
...For those who don't know (like me)... What does open loop vs. closed loop tell us about our engine??
Closed Loop: Input from the O2 sensors is being used in a feedback loop to keep your A/F ratio at 14.7:1 for maximum fuel economy and minimum emisssions. The feedback loop is connected, i.e. "closed."

Open Loop: Input from the O2 sensors is ignored. The feedback loop is disconnected, i.e. "open." The engine gets its fuel ratios from lookup tables, designed to richen the fuel mixture for maximum power and to keep from melting pistons, etc.
 

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So when *should* the system switch over from closed to open??
 

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Discussion Starter #8
pete1 said:
So when *should* the system switch over from closed to open??
L8apex1 said:
From my limited knowledge it will switch over to open when at WOT
That's exactly what I'm trying to determine. Join the discussion at: Tech Help needed - Throttle Position - ODBII vs. VAG-COM. Mine doesn't switchover at WOT - it switches over at a certain load value. We're trying to determine if that's normal behavior or if I have a bad Throttle Position Sensor.
 

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tested this out on the ride in to work on my 2004.5 1.8T (DBW)...

block 88 returns a bunch of generic binary bits.... :???:

block 99 shows STFT which does not match the "ADD" trim from block 32. but it does show O2-REG-ON/OFF.

I tested in 1st and 2nd gear from 1k rpm to redline @ WOT. the only time O2-REG-OFF is shown is at initial throttle tip-in, otherwise O2-REG-ON is active all the way to redline.

Also, O2-REG-OFF is shown during overrun/coast mode. the fuel trim in block 99 does go to 0.0% when "OFF". I have some logs to post later.

So it would seem the DBW cars operate in a different manner.
 

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From " A REAL MAF question... thread"
What are you calling the "lambda reading?" Field 3 in block 088? That's not a lambda value, those are the actual STFT's, which should be zero when in Open Loop. Gonna hafta think about that one, maybe even do some REsearch...

Yeah, this is a bit of a hijack, we should continue it in the other thread...
DBW has a block 088, but all it reads is binary bits. Block 099 reads rpm, coolant temp, lambda regulation as a % and lambda regulation ON/OFF. Field 3, the lambda regulation is flickering all over the place even at idle. It seems like a real time reading from the sensor, not the actual trim. It's probably the data that builds the trims which I undertood to be adjusted every x seconds or samples. In Reg OFF mode, these values were not zero. I think I can narrow this down by running block 099 with block 002, 114, 116, 118, 119 block 211, etc. I'm sure a pattern will show up.
 

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Discussion Starter #11
Block 099 reads rpm, coolant temp, lambda regulation as a % and lambda regulation ON/OFF. Field 3, the lambda regulation is flickering all over the place even at idle. It seems like a real time reading from the sensor, not the actual trim.
Should be the actual trim, i.e. the actual short-term, instantaneous, real-time lambda regulation. The trend or average of this regulation should be zero. If it's not, the LTFT (block 032) is adjusted to move the STFT average to zero. STFT will always flicker pos/neg.
 

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Rusty -- you just responded to a two-year-old post. :confused:
 

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Since I was good friends with Pete, I know he was just ribbing Rusty.
 

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Thanks, someday I would like to visit. My Dad's grandfather came over from Posen, Poland in 1885.
 

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Although this is a small off top - I am pleased to hear that you are "a little bit" Polish :) So remember that "Posen" is POZNAŃ in Poland today. we say it in Polish like something like POZNAñ
 

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50%, my Dad's mother came over in 1905.
 
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