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Old 04-09-2014, 07:52 AM   #1
pauly99
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LTFT and MAF - Correct Levels?

Just trying to dial in the different settings of the Torque Pro. This morning I took a drive and at idle and around 2000 RPM the LTFT was dead on stable at LTFT1 = 10.9 and LTFT2 = 11.7. What do these levels mean?
In comparison, what would LTFT tell you versus STFT?

MAF at idle was 3.4 or thereabouts and while going up a hill hit 56.7.

Are there standard levels for long term fuel trims, short term fuel trims, MAF, O2 sensors, and vacuum as it relates to an E46 particular model and year? In looking at my LTFT levels, I'm assuming the car is running lean? By the way, I drive a 2002 BMW 325i.
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Old 04-09-2014, 08:51 AM   #2
lszlszx
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Your LTFTs are too high. They should be within +/- 2-3.
STFT drive the LTFT, so keep an eye on the STFTs.
Look at your STFT at idle and at higher rpm driving.

Positive fuel trims mean that the computer is adding fuel, in other words the engine is running lean.

The MAF readings are about the same as mine.
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Old 04-09-2014, 09:06 AM   #3
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The LTFT's should be zero +-3 ideally. My 325i had similar fuel trims and was setting DTCs p0171 and p0174. I replaced the MAF sensor after searching for vacuum leaks and not finding any. My LTFT's were reduced by more than half. I would read Jfoj's thread and do some of the suggested diagnostics prior to purchasing any expensive parts.

http://forum.e46fanatics.com/showthread.php?t=897616

my thread with lots of Torque screenshots
http://forum.e46fanatics.com/showthread.php?t=1030545
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Old 04-09-2014, 09:18 AM   #4
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Ok. Thank you for the tips. I will check STFT levels when I head out to lunch.
I'm wondering if there are standard levels which are written for the various engine/vacuum/fuel delivery functions which our OBD's kindly spits out.

In regards to my car, I will re-look at possible vacuum leak sources although I have replaced quite a few things myself. Spark plugs were done about 2,500 miles ago. I have my eye on the DISA as well and replacing that as preventative maintenance.
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Old 04-09-2014, 09:24 AM   #5
pauly99
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TFT, thanks for the threads to read. Looks like some good reading there and that is what I better do. I'm not throwing any codes but the ride does feel sluggish to me.


Quote:
Originally Posted by TFT View Post
The LTFT's should be zero +-3 ideally. My 325i had similar fuel trims and was setting DTCs p0171 and p0174. I replaced the MAF sensor after searching for vacuum leaks and not finding any. My LTFT's were reduced by more than half. I would read Jfoj's thread and do some of the suggested diagnostics prior to purchasing any expensive parts.

http://forum.e46fanatics.com/showthread.php?t=897616

my thread with lots of Torque screenshots
http://forum.e46fanatics.com/showthread.php?t=1030545
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Old 04-09-2014, 11:03 AM   #6
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This is a good subject. What should normal STFT levels be?
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Old 04-09-2014, 11:54 AM   #7
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OP, just curious, do you have INPA? Just wondering how those values translate into the additive and multiplicative values in INPA.
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Old 04-09-2014, 01:01 PM   #8
pauly99
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Because I'm not sure what INPA is, I can answer no with no confidence whatsoever. Actually I use the V1.5 ELM327 OBD2 Bluetooth Car Wireless Scanner Diagnostic Tool for Android in combination with Torque Pro.

The attached is the STFT levels at idle.

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OP, just curious, do you have INPA? Just wondering how those values translate into the additive and multiplicative values in INPA.
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Old 04-09-2014, 02:51 PM   #9
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Quote:
Originally Posted by KaktusJaque View Post
This is a good subject. What should normal STFT levels be?

It's not quite that easy. Think of the STFT as an adjustment value to the LTFT which is sort of a long term average of the STFT.. So if your LTFT is at +10 and your STFT is averaging (it bounces around if you look at real time data) a positive number, then the LTFT will continue to go up. If STFT averages zero, LTFT will stay where it is. If STFT averages a negative number it will drive LTFT down (in the case of LTFT being +10)

In the example provided by the op, STFT is a snap-shot value so no guess can be made from that. Best thing to do is focus on LTFT. OP- the CEL will flag at +/- 10% so you likely have a vacuum leak or bad DISA.



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Old 04-09-2014, 04:32 PM   #10
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Ok. STFT was jumping up a bit from negative to positive. Mainly between + or - 3% while at idle. I do not have any codes but the car has been a bit sluggish and I'd like to bring down those LTFT numbers. I've been changing a couple of the vacuum lines/boots. ie the upper boot, secondary air pump, had to change out the F connector on the upper boot, and I was told the lower boot had been previously swapped out within the past 2 years. However since I did not have a receipt showing previous maintenance, I just ordered and received the lower boot in the mail yesterday. My plan is to change the DISA and that may come in the next few days before I was going to do a cooling system refresh.




Quote:
Originally Posted by Yewzer B Lewzer View Post
In the example provided by the op, STFT is a snap-shot value so no guess can be made from that. Best thing to do is focus on LTFT. OP- the CEL will flag at +/- 10% so you likely have a vacuum leak or bad DISA.
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Old 04-09-2014, 04:38 PM   #11
Yewzer B Lewzer
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LTFT and MAF - Correct Levels?

Quote:
Originally Posted by pauly99 View Post
Ok. STFT was jumping up a bit from negative to positive. Mainly between + or - 3% while at idle. I do not have any codes but the car has been a bit sluggish and I'd like to bring down those LTFT numbers. I've been changing a couple of the vacuum lines/boots. ie the upper boot, secondary air pump, had to change out the F connector on the upper boot, and I was told the lower boot had been previously swapped out within the past 2 years. However since I did not have a receipt showing previous maintenance, I just ordered and received the lower boot in the mail yesterday. My plan is to change the DISA and that may come in the next few days before I was going to do a cooling system refresh.

Sounds like you already ordered the DISA. It can be tested however by removing and inspecting the flap and a quick test of the diaphragm.


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Old 04-09-2014, 04:43 PM   #12
pauly99
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Quote:
Originally Posted by Yewzer B Lewzer View Post
Sounds like you already ordered the DISA. It can be tested however by removing and inspecting the flap and a quick test of the diaphragm.
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Actually I mis-typed. I haven't ordered the DISA yet. Doing research on OEM, Dorman, Vaico, GAS, etc...
I don't mind swapping it out only because I'm not sure if it has ever been replaced. Although I realize it is a quick 10 minutes (well half an hour for me) to check on its condition.
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Old 04-09-2014, 07:11 PM   #13
Yewzer B Lewzer
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I would test it and do the GAS kit if the flap is bad and the diaphragm is good.


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Old 04-09-2014, 08:26 PM   #14
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LTFT and MAF - Correct Levels?

Quote:
Originally Posted by lszlszx View Post
Might be a weak fuel pump if it feels sluggish and running lean.

Good point


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Old 04-10-2014, 09:16 AM   #15
pauly99
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Alright. You've given me a few things to look at. I have the day off tomorrow so I'll pick up the back seat and see if the liner has been torn (indication that the fuel pump may have been changed). If not, I know from reading a thread with like 44 pages that the fuel pump is on borrowed time.

I'll also be checking (pulling) the DISA valve and I'm not so sure if there is a test for it in regards to performance but I'll be spraying the MAF with MAF cleaner. Hopefully I will also be able to replace the lower intake boot (dunno what it takes to do that at the moment).


Quote:
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Might be a weak fuel pump if it feels sluggish and running lean.
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Old 04-10-2014, 09:49 AM   #16
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Here is a link with good fuel trim info:

http://www.bmwicom.net/wp-content/up..._fuel_trim.pdf

Code:
BMW Fuel Trim (MS42)
  Nominal Value    Range          Limit
LTFT 0 ms          0.35 ms      >12% for 10 seconds
STFT 0 %           8%           >8% for 10 seconds
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Old 04-10-2014, 10:20 AM   #17
KaktusJaque
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Quote:
Originally Posted by shanneba View Post
Here is a link with good fuel trim info:

http://www.bmwicom.net/wp-content/up..._fuel_trim.pdf
Thanks shanneba, document read and saved for future reference.
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Old 04-11-2014, 03:06 PM   #18
pauly99
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Pulled DISA valve today. Good tension. Pin is fine. Diaphragm however I believe has issues. Put my finger over the hole while the flap was open. Again, good tension on the flap but it slowly closed while my finger remained over the hole. O-ring was flat.

New lower intake boot. Sprayed MAF with MAF cleaner. Attached everything. We'll see if things are any better. Perhaps I cleared up a vacuum leak.

Removed rear seat. Might be hard to tell but I cannot see that the fuel pump was ever changed out. The felt was not cut or anything.

So I might have a couple of project that I will need to do over the coming weeks.
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Old 04-11-2014, 04:40 PM   #19
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I will toss my $0.02 in here.

I deal with a lot of cars, BMW and others.

Here is my rule of thumb.

LTFT are mainly what I worry about, expect them to almost always to be between 0% and + 3%. My preference is to see the LTFT to stay in the range of 0% to +2.5%, I do not get too worried until they are over +3% and encroaching +4%. On my personal vehicles I attempt to keep them between 0% and +2.5% but on a customers car, many do not want to spend the money to chase the last 1.5% or so of fuel trim.

Rarely will the fuel trim ever be negative. If it is, usually means there is a pretty obvious problem that may need to be resolved.

Also keep in mind under deceleration/coast there can be fuel cut off and the fuel trims can jump very high one way or another during a coast with fuel cut off, this is normal.

In general the MAF and O2 sensor control the fuel trim for the most part. Throttle position can play into fuel trim as well.

Unless there is something way out of whack like crappy aftermarket or the wrong type of O2 sensor or a Asian clone/counterfeit MAF the fuel trims are almost always going to be on the Lean side or postive (+) by 10% or more.

Short Term Fuel Trim values do dance around, that is how they are supposed to react, however, some situations will cause the STFT to stay very high and stable at idle or even cruising. One test I usually do it to remove the oil fill cap on the E46 while the engine is running. An engine with a pretty tight crankcase will have the STFT values immediately jump by 20-25% and then drop back down to where you started quickly once the oil fill cap is replaced.

If the crankcase is not tight, you probably not see the immediate STFT jump of 20% or more.

This is where an OBDII scan tool that displays Live/Real Time data can be very useful. No need for a BMW specific scan tool for these jobs and many times they actually provide less useful data.
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Old 04-11-2014, 05:08 PM   #20
pauly99
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I didn't check the name stamped on the MAF sensor when I removed it to check the DISA valve but I am hoping the previous owner didn't put in cheap parts. The car feels like it is running smoother but the numbers don't reflect that. The LTFT was between 8.6% and 10.9% at idle once the car was warmed up and driven a few minutes ago. Nice having new rubber (boots) and a new F connector on there now though.

So per JFOJ, sounds like I should be checking my MAF sensor and O2 sensors. Can the O2 sensors be checked (values)?
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