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Old 11-06-2012, 09:21 AM   #21
flashmeow
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I think you are analyzing your long fuel trim incorrectly.

the nomimal value for the long term (multiplicative) is 0% and anything +/- 8% is considered good.

therefore anything that falls in the range of:

-8, -7, -6, -5, -4, -3, -2, -1, [0], 1, 2, 3, 4, 5, 6, 7 8

is considered good.

you got -6.5% so this falls within that +/-8% of your nomimal value (0). this is why there are no CEL/SES code.

You are good.

case close.

but... your spark plug does look strange to me though . does all spark plugs look like that one you showed?
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Old 11-06-2012, 09:57 AM   #22
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I have to disagree that "everything is good" if the fuel trims are between +/-8%.

I look at cars all day long and even at close to 3% I am not satisfied. And this is +3% not -3%.

A "normal" properly operational engine will have fuel trims typically less than +3% and never in the negative region. What I usually see is in the are of +2% or less, this is what I would consider as "normal".

There should be VERY few situations where the car is running rich and is required to reduce the injector timing to lean the mixture out. This is usually indicating an issue with under reporting of airflow from my experience. Many times this is due to a wrong MAF and/or cheap aftermarket MAF.

So I would say this is anything but case closed.

Long term fuel trims usually are based more upon cruise conditions and if the engine is running lean due to a bad MAF or other sensor, then you can likely cause long term damage such as burnt valves and other symptoms of overly high combustion chamber temps.
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Old 11-06-2012, 03:39 PM   #23
flashmeow
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Quote:
Originally Posted by jfoj View Post
I have to disagree that "everything is good" if the fuel trims are between +/-8%.

I look at cars all day long and even at close to 3% I am not satisfied. And this is +3% not -3%.

A "normal" properly operational engine will have fuel trims typically less than +3% and never in the negative region. What I usually see is in the are of +2% or less, this is what I would consider as "normal".

There should be VERY few situations where the car is running rich and is required to reduce the injector timing to lean the mixture out. This is usually indicating an issue with under reporting of airflow from my experience. Many times this is due to a wrong MAF and/or cheap aftermarket MAF.

So I would say this is anything but case closed.

Long term fuel trims usually are based more upon cruise conditions and if the engine is running lean due to a bad MAF or other sensor, then you can likely cause long term damage such as burnt valves and other symptoms of overly high combustion chamber temps.
You have a lot of useful points but the fact of the matter is anything that is +/- 8% from the nomimal number is consider within spec and as a result is acceptable to the DME.

The DME only reports a lean or rich code if either the LTFT or STFT reading does not meet the range requirement.

A perfect engine (which is virtually impossible) will report a LTFT of 0ms and a STFT of 0%. Since a perfect engine doesn't exist, a number closest to 0ms and 0% is perfer. This mean that a car that has a 3% STFT is more effecient than an car with 6.5%. However, both cars are operating under spec and the DME is able to adjust the fuel trim according.

The adaptation system can only make slight corrections and can not compensate for large changes which may be encountered as a result of incorrect airflow or incorrect fuel supply to the engine. Therefore, anything +/_ is good although it is not "perfect." His car is able to adapt and is adapting to specification


To the OP:

In order to maintain an "ideal" air/fuel ratio, the engine control module is capable of adapting to various environmental conditions encountered while the vehicle is in operation (i.e. changes in altitude, humidity, ambient temperature, fuel quality, etc.).

Within the areas of adjustable adaption, the engine control module modifies the injection rate under two areas of engine operation:

1. During idle and low load mid range engine speeds (Additive Adaptation),
2. During operation under a normal to higher load when at higher engine speeds (Multlplicative Adaptation).

For MS42 (and newer e46 DME) the LTFT and STFT ranges are:

LTFT 0ms (Nominal value) +/- 0.35mns
STFT 0% (Nominal Value) +/- 8%

If a LTFT adaptation value is positive (+) than the DME thinks the mixture is lean (a lack of fuel or too much air is present). As a result, the engine control module is trying to en-richen the mixture

If a LTFT aptation value is negative (-) than the DME thinks the mixture if rich (too much fuel or lack of air). This could be due to a leaking injector or a stuck open pintle supply too much fuel. As a result, the engine Control
Module is trying to lean-out the mixture

If a STFT Adaptation Value is postive (+) then the DME thinks mixture is lean. A consistent high positive value can mean bad MAF (reporting measured volume too low), low exhaust back pressure, blown TWCC, misfires, large intake or exhaust leak (Large air volume).

If a STFT Adaptation Value is negative (-) then the DME thinks mixture is rich. A consistent high negative value can mean high exhaust back pressure, clogged TWCC, injectors stuck open.
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Old 11-06-2012, 04:11 PM   #24
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Great information, guys. I will look mine up today out of curiosity.
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Old 11-06-2012, 04:19 PM   #25
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Originally Posted by E46Mango View Post
Great information, guys. I will look mine up today out of curiosity.
me too for my engine swap project. I have driven over 350 miles and have no lean/rich codes. I am going to post my LTFT/STFT tonight!!!
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Old 11-06-2012, 04:28 PM   #26
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Originally Posted by flashtwosix View Post
me too for my engine swap project. I have driven over 350 miles and have no lean/rich codes. I am going to post my LTFT/STFT tonight!!!
Hell yeah! LTFT/STFT party! WHO'S IN??
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Old 11-06-2012, 06:17 PM   #27
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please see http://forum.e46fanatics.com/showpos...&postcount=410

for my LT/ST fuel trim numbers. impressive if I don't say so myself
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Old 11-06-2012, 06:17 PM   #28
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Quote:
Originally Posted by flashtwosix View Post
You have a lot of useful points but the fact of the matter is anything that is +/- 8% from the nomimal number is consider within spec and as a result is acceptable to the DME.
Well this is where we will have to differ and you will also have to understand the difference between "spec" and "range". You also have to clearly understand where I am coming from and realize I have probably been working on car longer than you have been alive.

Just because a value is within a range that does not trigger a fault code does not mean the value is in "spec" or even in the "nominal range".

So if you allow a vehicle to sit at a +8% range, it takes VERY little to push the value over the edge to the point that fault codes will be triggering very often. This is exactly why the "range" is so wide, it is to eliminate annoying fault codes to the point that the driver thinks the car is crying wolf and has a major problem.

Quote:
Originally Posted by flashtwosix View Post
The DME only reports a lean or rich code if either the LTFT or STFT reading does not meet the range requirement.
This is a relatively correct statement, there are also a few different sets of fault codes to give someone that understands the faults as to how far out of range the problem(s) is/are.

Quote:
Originally Posted by flashtwosix View Post
A perfect engine (which is virtually impossible) will report a LTFT of 0ms and a STFT of 0%. Since a perfect engine doesn't exist, a number closest to 0ms and 0% is perfer. This mean that a car that has a 3% STFT is more effecient than an car with 6.5%. However, both cars are operating under spec and the DME is able to adjust the fuel trim according.
First off there are "perfect engines" in the world, matter of fact there are far more "perfect engines" than you might think. But it is more than just the "perfect engine", it is a combination of a mechanical sound engine, properly operating sensors, quality spark, fuel delivery and fuel. I have seen many vehicles with between 60-90k miles with minimal maintenance and mostly original sensors that do not deviate into the +3% range at all. Matter of fact my threshold that I have come to apply and expect have been from all the vehicles that I have monitored fuel trims on over the years.

Quote:
Originally Posted by flashtwosix View Post
The adaptation system can only make slight corrections and can not compensate for large changes which may be encountered as a result of incorrect airflow or incorrect fuel supply to the engine. Therefore, anything +/_ is good although it is not "perfect." His car is able to adapt and is adapting to specification.
This is generally a correct statement. However, again, I rarely see cars that report rich conditions where the DME is having to take fuel out of the equation. Almost all of the cars I have looked at with fuel trims in the negative range have usually had a pretty severe sensor issue. Many times MAF that under reports airflow, which is pretty common as the thin wire oxidizes and the oxidation acts as an insulation layer or in a case where an improper or poor quality aftermarket MAF is installed. I have also seen issues where engine cooling temperature being slightly low will also cause this condition where in the same situation, the engine temperate may not be in "spec" but it is within a "range" that is does not trigger any faults.

In the age where everyone expects some tool or readout to provide "x" value and if that value is in an expected range that does not trigger a fault, you really need to dig deeper down in your mind and look at what the rest of the world looks like from the 10,000 foot view. If you have looked at hundreds of cars over the years and you see a specific trend that is on the low end of a "range", then this is really what your "spec" should become.

I have had cars that clearly had problems, with fuel trims not triggers faults, where clear problems were identified and repaired and fuel trims were then typically back under +2%.

Case in point, I have 4 vehicles in my driveway. The youngest is a 2005, the oldest is 2003, the lowest mileage is 75k highest mileage is 100k. All my cars have all original sensors and some have minimal maintenance and all my cars are in the positive fuel trims and non higher than 3%.

If any of my cars get beyond positive 3% I am looking for issues. If any of my cars were beyond negative 1% I would also be looking for issues.

My 2003 VW 1.8t with 75k miles and all original sensors, maybe 1 set of spark plugs a while ago is very close to 0% STFT, it does vary slightly and 0 LTFT. This car dues have a cold start issue, but with 3 intake valves per cylinder (5 valves per cylinder total), I believe the cold start issue is carbon deposits build up on the back of the intake valves and the intake port. This does not cause a problem with fuel trims as the carbon acts as a sponge. After the car sits overnight, the fuel in the porous carbon evaporates and then when the car is started first thing for the day, the porous carbon absorbs fuel for the first 20-30 seconds causing a momentary lean condition then once the carbon is fuel saturated, it is not a significant problem.

This issue does not show up in the fuel trims or any other driving condition, just cold starts. The correct and fastest way to resolve the problem is removing the intake and walnut shell blasting all the carbon off the intake valves and intake ports, but I am taking a slower maintenance approach as it is my car and I can manage the problem. If it was a customer car, the walnut shell blasting would likely be the solution.

So back to the OP, he has symptoms that really do not agree with a slightly rich mixture. His plugs look like they are lean and running hot, as well as other driveability issues. I am not there to diagnose the engine, but my first and most obvious thing I look at in these cases is the MAF to make sure there is no under reporting of airflow. Then depending on what I find, I move on to many other diagnostic tests to determine why a engine is trying to remove fuel as this deviates very much from the norm of issues that I typically see.

I just want to make absolutely sure on a DIY Internet forum I do not in my opinion leave DIY types with the impression that fuel trims consistently running about 3% are considers "normal" and within "spec" as from my observations this is NOT the case.
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Last edited by jfoj; 11-06-2012 at 06:22 PM.
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Old 11-06-2012, 06:35 PM   #29
flashmeow
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Quote:
Originally Posted by jfoj View Post
Well this is where we will have to differ and you will also have to understand the difference between "spec" and "range". You also have to clearly understand where I am coming from and realize I have probably been working on car longer than you have been alive.

Just because a value is within a range that does not trigger a fault code does not mean the value is in "spec" or even in the "nominal range".

So if you allow a vehicle to sit at a +8% range, it takes VERY little to push the value over the edge to the point that fault codes will be triggering very often. This is exactly why the "range" is so wide, it is to eliminate annoying fault codes to the point that the driver thinks the car is crying wolf and has a major problem.



This is a relatively correct statement, there are also a few different sets of fault codes to give someone that understands the faults as to how far out of range the problem(s) is/are.



First off there are "perfect engines" in the world, matter of fact there are far more "perfect engines" than you might think. But it is more than just the "perfect engine", it is a combination of a mechanical sound engine, properly operating sensors, quality spark, fuel delivery and fuel. I have seen many vehicles with between 60-90k miles with minimal maintenance and mostly original sensors that do not deviate into the +3% range at all. Matter of fact my threshold that I have come to apply and expect have been from all the vehicles that I have monitored fuel trims on over the years.



This is generally a correct statement. However, again, I rarely see cars that report rich conditions where the DME is having to take fuel out of the equation. Almost all of the cars I have looked at with fuel trims in the negative range have usually had a pretty severe sensor issue. Many times MAF that under reports airflow, which is pretty common as the thin wire oxidizes and the oxidation acts as an insulation layer or in a case where an improper or poor quality aftermarket MAF is installed. I have also seen issues where engine cooling temperature being slightly low will also cause this condition where in the same situation, the engine temperate may not be in "spec" but it is within a "range" that is does not trigger any faults.

In the age where everyone expects some tool or readout to provide "x" value and if that value is in an expected range that does not trigger a fault, you really need to dig deeper down in your mind and look at what the rest of the world looks like from the 10,000 foot view. If you have looked at hundreds of cars over the years and you see a specific trend that is on the low end of a "range", then this is really what your "spec" should become.

I have had cars that clearly had problems, with fuel trims not triggers faults, where clear problems were identified and repaired and fuel trims were then typically back under +2%.

Case in point, I have 4 vehicles in my driveway. The youngest is a 2005, the oldest is 2003, the lowest mileage is 75k highest mileage is 100k. All my cars have all original sensors and some have minimal maintenance and all my cars are in the positive fuel trims and non higher than 3%.

If any of my cars get beyond positive 3% I am looking for issues. If any of my cars were beyond negative 1% I would also be looking for issues.

My 2003 VW 1.8t with 75k miles and all original sensors, maybe 1 set of spark plugs a while ago is very close to 0% STFT, it does vary slightly and 0 LTFT. This car dues have a cold start issue, but with 3 intake valves per cylinder (5 valves per cylinder total), I believe the cold start issue is carbon deposits build up on the back of the intake valves and the intake port. This does not cause a problem with fuel trims as the carbon acts as a sponge. After the car sits overnight, the fuel in the porous carbon evaporates and then when the car is started first thing for the day, the porous carbon absorbs fuel for the first 20-30 seconds causing a momentary lean condition then once the carbon is fuel saturated, it is not a significant problem.

This issue does not show up in the fuel trims or any other driving condition, just cold starts. The correct and fastest way to resolve the problem is removing the intake and walnut shell blasting all the carbon off the intake valves and intake ports, but I am taking a slower maintenance approach as it is my car and I can manage the problem. If it was a customer car, the walnut shell blasting would likely be the solution.

So back to the OP, he has symptoms that really do not agree with a slightly rich mixture. His plugs look like they are lean and running hot, as well as other driveability issues. I am not there to diagnose the engine, but my first and most obvious thing I look at in these cases is the MAF to make sure there is no under reporting of airflow. Then depending on what I find, I move on to many other diagnostic tests to determine why a engine is trying to remove fuel as this deviates very much from the norm of issues that I typically see.

I just want to make absolutely sure on a DIY Internet forum I do not in my opinion leave DIY types with the impression that fuel trims consistently running about 3% are considers "normal" and within "spec" as from my observations this is NOT the case.
point taken.

BH
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Old 03-07-2013, 07:37 AM   #30
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Quote:
Originally Posted by E46Mango View Post
Hell yeah! LTFT/STFT party! WHO'S IN??
The last data I have recorded for my 330Ci with fuel trims shows:

STFT - Additive bank 1 - +0.06ms
STFT - Additive bank 2 - +0.05ms

LTFT - Multiplicative bank 1 - -8.0%
LTFT - Multiplicative bank 2 - -8.0%

My car has always been at about -8.0% multiplicative since the Dinan stage 2 software and BMW Performance Intake was installed. I noticed that the day after I had the software update installed.
Never had any fuel mixture codes.

An older file showed multiplicative trims in the +4.5% range.
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Old 03-07-2013, 08:08 AM   #31
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Dinan, what can I say, I will not even start with the issues I had with my no longer installed Dinan software on my M5. It was in the car when I purchased it and I had almost 2 years of headaches until I figured the problem was the software!

Dinan folks are the most ARROGANT people I have EVER dealt with. Their attitude is the problem is ALWAYS with the car!

Anyway, I see you have a 330. Long term @ -8.0% is out there. Likely not enough to trigger a CEL, but not where I would like to see the figures.

This means likely the engine is running consistently rich? Rarely do engines run rich, but hard to say with the Dinan software installed.

But I would really question your MAF. Have seen a LOT of 330's lately with very high LTFT figures, usually toward the positive side.

If you get a chance to borrow a MAF off a similar 330 that is running well, it would be an interesting test to see if there is any change to the LTFT.
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