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Author Topic: 1.8T engine is running too rich - Long Term Fuel Trim -19% please help :(  (Read 81219 times)
Malinovsky
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hi
problem like in topic.
In Group 032: 001F (rkat_w), 0021 (fra_w),
my fra_w value goes to about -18% and stays on this level :/
A can reset ECU to get 0% but after throttle body adaptation it goes back to -18%
In my opinion this LTFT changes like mostly because of driving at 2000-3000 rpm,
because this is when my STFT values fr_w (or frm_w - same value on my car) goes down to big minus.

I spent a lot of time and money for changing parts (maf, o2 sensor etc.) and finding what cause the problem, but still got nothing Sad

The patient is Audi TT mk1 180hp quattro, with OEM ECU soft with some mods like TIP, FMIC, Catback exhaust and amsoil air filter. I have the problem since I bought the car.

this is my log on 3gear from about 1500 till red.
I'm putting the log as a link + original log file as attachment
log link: http://vaglog.rtnet.pl/soulx666_132405.html

please help Sad
any suggestions or log interpretations will be great



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vdubnation
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were injectors or fpr changed ?
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userpike
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if the injectors are stock and stock FPR, you need to perform vacuum and boost leak tests. When looking at block 32, if the values are > +/-5% indicates either a boost or vacuum leak in the system.

If the injectors are aftermarket and tuned for in your ECU, hopefully the tuner tested for leaks before they used block 32 to tune for the injectors.
I guess if you recorded the values that were in block 32 before and used those as your zero point you could still tune for injectors with vacuum/boosts leaks in the system but why would want to do that? leaks are just bad news.
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nyet
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Dont bother doing any pulls until you fix your intake leaks and your trims are stable.
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Malinovsky
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Well the problem is not that easy  Wink
But I wanted to hear your first shots before I will give you the full story.

This is what I've already did.

a/ I did leak test many times by putting psi into TIP starting from 0 and going up til 15 psi.
Got nothing.
here you have some vid from my leak tests:
http://youtu.be/GHUH-R3qYoE
http://youtu.be/_FDlkEGBG-0

b/
injectors are stock. I checked all 4 and replaced o-rings.
They are perfect dry on car - no leaking fuel.
And this is how they run:
http://youtu.be/8zKOsrPgqZk

c/I changed smic to FMIC and bought new turbo outlet pipe and all hoses.
So I'm 100 % sure that I have no leaks on a way from air filter to turbo, from turbo to fmic and from fmic to intake manifold.
Vacuum hoses also checked and changed.

d/ I checked fuel pump by doing performance test from bentley manual (fuel delivery rate checking) - quantity of delivered fuel was fine.

e/ I have stock fpr (3 bar). Also checked.
I replaced mine for tests with second one from a car with perfect trims and still got the problem. So this is not FPR fault.

f/ I also bought a new OEM MAF and O2 sensor. Both changed for factory new TWICE to be sure.

As you can see I did a lot and still have no clue what did I miss.
Looks like everything is fine, but trims are showing the true.
I studied a lot about how LTFT works to understand why my trim goes down and down. But also got no new informations.
I would like to know from what values ECU gets data to create LTFT (fra_w).
There MUST be something that I missed.
Maybe you can see something more than fra_w on my log that is wrong or should I make any other type of log to know something new ?

 
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nyet
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How about stock ecu?
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ECUx Plot
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Please do not ask me for tunes. I'm here to help people make their own.

Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience.
userpike
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Well the problem is not that easy  Wink
But I wanted to hear your first shots before I will give you the full story.

This is what I've already did.

a/ I did leak test many times by putting psi into TIP starting from 0 and going up til 15 psi.
Got nothing.
here you have some vid from my leak tests:
http://youtu.be/GHUH-R3qYoE
http://youtu.be/_FDlkEGBG-0

b/
injectors are stock. I checked all 4 and replaced o-rings.
They are perfect dry on car - no leaking fuel.
And this is how they run:
http://youtu.be/8zKOsrPgqZk

c/I changed smic to FMIC and bought new turbo outlet pipe and all hoses.
So I'm 100 % sure that I have no leaks on a way from air filter to turbo, from turbo to fmic and from fmic to intake manifold.
Vacuum hoses also checked and changed.

d/ I checked fuel pump by doing performance test from bentley manual (fuel delivery rate checking) - quantity of delivered fuel was fine.

e/ I have stock fpr (3 bar). Also checked.
I replaced mine for tests with second one from a car with perfect trims and still got the problem. So this is not FPR fault.

f/ I also bought a new OEM MAF and O2 sensor. Both changed for factory new TWICE to be sure.

As you can see I did a lot and still have no clue what did I miss.
Looks like everything is fine, but trims are showing the true.
I studied a lot about how LTFT works to understand why my trim goes down and down. But also got no new informations.
I would like to know from what values ECU gets data to create LTFT (fra_w).
There MUST be something that I missed.
Maybe you can see something more than fra_w on my log that is wrong or should I make any other type of log to know something new ?

 


hmm... no "soapy water in a spray bottle" method? do another leak test...

What's the PCV system looking like? Are you absolutely sure the check valve between the intake and PCV system is closing properly during boost? If the vacuum amplifier in the PCV system is failing you'll get boost leakage into the PCV also. It doesn't take much for them to gum up and allow boost to leak. What about the pressure regulating valve that is mounted in the TIP? If it fails you'll get the boost leak dtc.

With your -18% trim the ECU is removing 18% of the fuel that it SHOULD need. This is happening because the air mass that is supposed to mix with that fuel is escaping the system somewhere. I know of no other explanation because you said the injectors are stock. If the number is positive the ECU is adding fuel to compensate for the extra air mass in the system (vacuum leak)

Good luck! I hope you figure out the problem sooner than later.

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hammersword
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Hi,

What I believe is
1) FPR stuck
2) wrong MAF sensor
3) mapping issue

Please post your ECU file here

There are no leaks because the LTFT is -18% so ecu removes fuel. When you have leaks MAF counts lower and ECU adds fuel so it should be +18% for leaks!

Regards,
Fotis
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I had a problem a near the FMIC leak (after the Maf obviously) , so the maf counted for X amount of air but in the end there was X/2 air going in the chamber ,so it removed (negative LTFT) fuel Smiley Smiley
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userpike
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This is by far the easiest explanation to understand on fuel trims and it's creditable.

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info
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userpike
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I want to add in here that you should perform the leak testing on a fully warmed up engine. It's a PITA but sometimes leaks only happen when the engine is hot. Also, utilize a test pressure much higher than you ever intend on the turbocharger boosting. Use the "soapy water in a spray bottle" boost leak detection method and watch for bubbles! Cheesy
« Last Edit: June 26, 2013, 12:12:39 PM by userpike » Logged
Malinovsky
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hmm... no "soapy water in a spray bottle" method? do another leak test...
how to get any results during this test if there is underpressur in the system?

What's the PCV system looking like? Are you absolutely sure the check valve between the intake and PCV system is closing properly during boost? If the vacuum amplifier in the PCV system is failing you'll get boost leakage into the PCV also. It doesn't take much for them to gum up and allow boost to leak.
OEM pcv system is out including pcv valve.
I changed pcv system to closed oil catch tank system
you can see it here on my car:



What about the pressure regulating valve that is mounted in the TIP? If it fails you'll get the boost leak dtc.
do you mean DV valve?
if yes, it is changed to new made by forge.

With your -18% trim the ECU is removing 18% of the fuel that it SHOULD need. This is happening because the air mass that is supposed to mix with that fuel is escaping the system somewhere. I know of no other explanation because you said the injectors are stock. If the number is positive the ECU is adding fuel to compensate for the extra air mass in the system (vacuum leak)
and what IF ecu by this -18% is removing fuel that SHOULDN'T be there?
my car is using more fuel during drive than it should, so maybe I realy have to rich mixture during normal daily drive?
during logs STFT is perfect, so you can even see on log that during making it my LTFT is getting better because of perfect STFT
but during normal city drive STFT values goes to big minus values. In my opinion this is the cause of my big LTFT,
but I still can't find why my STFT goes down during calm daily city drive.
Is injector time value correct on my log?
Maybe there is any other sensor connected with fueling or air in car that is broken and gives wrong values to ecu so injectors have wrong timing during city drive?
In my opinion injectors are fine but are working wrong because of ecu. Is this theory possible?
 

How about stock ecu?
you think that my stock ecu can be damaged  Huh


What I believe is
1) FPR stuck
nope - like I said - I swapped my fpr with one from car with no trim problems - and I still got same trim problem after ecu reset on my car
so it's definitly not a fpr fault

2) wrong MAF sensor
nope, bought 2 OEM factory new bosh maf dedicated by numbers for my car
3) mapping issue
what do you mean ? and how can I check it ?
Please post your ECU file here
I will

There are no leaks because the LTFT is -18% so ecu removes fuel. When you have leaks MAF counts lower and ECU adds fuel so it should be +18% for leaks!
yeap, I also think that this is not a leak problem,
but like I wrote before I double checked it anyway

I want to add in here that you should perform the leak testing on a fully warmed up engine. It's a PITA but sometimes leaks only happen when the engine is hot. Also, utilize a test pressure much higher than you ever intend on the turbocharger boosting. Use the "soapy water in a spray bottle" boost leak detection method and watch for bubbles! Cheesy
hmm on hot engine? I will try it
Is there any sense in this soapy water leak test here?
I mean there is underpressure in the system so I won't see aby bubbles anyway...
Am I wrong here? How should I perform this test with underpressure in the system?

This is by far the easiest explanation to understand on fuel trims and it's creditable.

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info
thanks I know this one, and a few more, including OEM bosh service manual.
I understand the theory - I mean I know how it works,
what I don't know is how exacly LTFT value is creating by the ECU,
are there any car sensors (more than maf and o2) connected with the proces so I can check it?
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ddillenger
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I'd be willing to bet you have the wrong MAF.
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vdubnation
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have you tried running the maf unplugged ?
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hammersword
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I had a problem a near the FMIC leak (after the Maf obviously) , so the maf counted for X amount of air but in the end there was X/2 air going in the chamber ,so it removed (negative LTFT) fuel Smiley Smiley

Yes! MAF reads half the airflow -> tell to ECU to inject half times -> leaner AFR -> O2 reads leaner than 14.7 -> O2 controler add fuel to hit the lambda = 1 target -> STFT = positive
It is classic if you see 20-25% and it still misfire in idle Tongue
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