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Thread: BLM- Long term fuel trim?

  1. #1
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    BLM- Long term fuel trim?

    What does BLM represent? I have a 1989 Chev K1500 350 with a 1227747 ASDU computer. I have both the TunerPro Rt program and the WIN ALDL program. I am trying to find out why my engine will not run correctly when the alternator is charging? I can unplug the single signal wire to the alternator and the engine will smooth out. When the wire is plugged in the motor will go down when accelerating and continues to surge. The tuner program shows a fault [in red] 155 BLM long term fuel trim? When running at less than 12V the number is 128 BLM. If I stay in the throttle long enough the INT fuel trim will go red also? Any help will be appreciated. Thanks G.S.

  2. #2
    Fuel Injected! steveo's Avatar
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    they're simple.

    blm is block learn mode, int is the integrator

    those values are what the ecm uses to correct your air/fuel ratio when the o2 sensor is active

    128 is "perfect". less than 128 means it thinks your car was running rich (fuel is being subtracted to fix it), more means that it was running lean so fuel was added.

    the integrator acts first, then the values are stored in blm, so it can "remember" how to correct your fueling.

    155 means it was leaning out (or it thinks it was) and its added a bunch o fuel.

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    Fuel Injected! 84Elky's Avatar
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    What does BLM represent? I have a 1989 Chev K1500 350 with a 1227747 ASDU computer. I have both the TunerPro Rt program and the WIN ALDL program. I am trying to find out why my engine will not run correctly when the alternator is charging? I can unplug the single signal wire to the alternator and the engine will smooth out. When the wire is plugged in the motor will go down when accelerating and continues to surge. The tuner program shows a fault [in red] 155 BLM long term fuel trim? When running at less than 12V the number is 128 BLM. If I stay in the throttle long enough the INT fuel trim will go red also? Any help will be appreciated. Thanks G.S.
    Please don't take this the wrong way because this appears to be your first post. There are many here more than willing to help, but perhaps you should first do some searching regarding what BLM represents as well as the effect of/reason for/need of the alternator signal wire. There are thousands of posts regarding each on this and other forums. That research may not answer your questions, but it may serve to refine them and will ensure that replies to your questions will make sense. In short, the ECM makes adjustments for battery or pump voltage to the injectors (depends on how the calibration is set-default likely the pump). But way too many variables at this point to speculate. Do some research and come back.

  4. #4
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by rudder2fly View Post
    What does BLM represent? I have a 1989 Chev K1500 350 with a 1227747 ASDU computer. I have both the TunerPro Rt program and the WIN ALDL program. I am trying to find out why my engine will not run correctly when the alternator is charging? I can unplug the single signal wire to the alternator and the engine will smooth out. When the wire is plugged in the motor will go down when accelerating and continues to surge. The tuner program shows a fault [in red] 155 BLM long term fuel trim? When running at less than 12V the number is 128 BLM. If I stay in the throttle long enough the INT fuel trim will go red also? Any help will be appreciated. Thanks G.S.
    All good advice above...

    But your issue is not the altenator or charging system. You just found a way to make BLM/Long Term Fuel Trim come to the number you wanted. It's probably loosing enough voltage to go Open Loop, so no O2 sensor feedback? Which would always be 128.

    You have TunerPro RT, so no reason to do data logs with ancient technology, WinALDL is like data in brale... get your ADX file and learn to data log with TunerPro. I know it's a little harder to get going but the results are well worth it and we can take a look at what your problem is.



    155 BLM is adding a lot of fuel. One thing this ECM can not do and does not know, it expects to be correct is fuel pressure. So you will need to check fuel pressure as well.

    Is the motor stock? Any mods done please list them.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Still working to learn a new laptop and the TunerPro RT program.

    Quote Originally Posted by EagleMark View Post
    All good advice above...

    But your issue is not the altenator or charging system. You just found a way to make BLM/Long Term Fuel Trim come to the number you wanted. It's probably loosing enough voltage to go Open Loop, so no O2 sensor feedback? Which would always be 128.

    You have TunerPro RT, so no reason to do data logs with ancient technology, WinALDL is like data in brale... get your ADX file and learn to data log with TunerPro. I know it's a little harder to get going but the results are well worth it and we can take a look at what your problem is.



    155 BLM is adding a lot of fuel. One thing this ECM can not do and does not know, it expects to be correct is fuel pressure. So you will need to check fuel pressure as well.

    Is the motor stock? Any mods done please list them.
    The motor is stock 350, good compression 170# all cycl. I have had a lot of trouble since Aug 2013. I thought I had a previous post on this forum concerning this truck. I thought I had finally got the engine running correctly then this happened. I really didn't want to drop another $500.00 in a laptop to figure this thing out let alone learn how to use this computer at 76 years old. As you know the manufactors do not supply you with a manual on how to use their products. I need something I can hold in my hand and read. In short the original problem was; it would not rev up in closed loop. The problem finally found to be the MAP sensor or so I thought. All the following has been replaced: fuel pump,IAC, ESC,TPS,OXYS,DIST,TEMPS,ECM,EGR,Complete TBI rebuild,Alternator, All grounds checked loosened and retightened. I probably forgot something as it seems I have been under this hood all summer. I will run the TunerProRt some more and try to learn how to use the program. Thanks GS

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    EFI GearHead ! EagleMark's Avatar
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    If you don't want to learn this stuff and just want to fix your truck? It's hardly worth the cost of a laptop just to data log for a issue like this.

    Seriously the fuel pressure being low is most likely the issue. New pump and all the parts does not mean they are all good. Heck you could have plugged up a filter?

    Most auto parts stores have loaner fuel pressure gauges. Your truck will have to be hooked up underneath at fuel filter. May as well buy the filter while you have it apart to test pressure!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  7. #7
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    Quote Originally Posted by EagleMark View Post
    If you don't want to learn this stuff and just want to fix your truck? It's hardly worth the cost of a laptop just to data log for a issue like this.

    Seriously the fuel pressure being low is most likely the issue. New pump and all the parts does not mean they are all good. Heck you could have plugged up a filter?

    Most auto parts stores have loaner fuel pressure gauges. Your truck will have to be hooked up underneath at fuel filter. May as well buy the filter while you have it apart to test pressure!
    I have done the fuelpressure check. 10 lbs with both the original pump and the new pump. Pressure checked at the TBI. Two new filters. I don't believe the truck would run good with the alternator not charging if fuel pressure were the problem. G.S.

  8. #8
    EFI GearHead ! EagleMark's Avatar
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    GM service manual says between 9-13 PSI!
    Yes it will run between 9-13 PSI.
    Most stock trucks I have checked over the years are 12. I can tell you from tuning that even a bone stock truck runs so much better at 13 PSI. At 10 PSI the BLMs are very high...

    Have you checked voltage AT fuel pump? Ground at frame off fuel pump? Low voltage at pump = low pressure. But your saying that disconnecting the altenator makes BLM 128 which is better? Makes no sense? If you can do this again when looking at data see if the data shows it is still in Closed Loop! If not in closed loop the BLM will be 128... usually...

    I'm only guessing you have no error codes set? As that would be first thing to check and some how you are seeing BLM data.

    When you see the INT/Short Term Fuel Trim go red, it is just the program warning you the numbers are getting high. For the BLM/Long Term Fuel Trim 155 is still within boundaries of the ECM adjustment to fuel, IIRC the max BLM in ASDU is 172. So really not a big thing and if you were not a GearHead you would never know. But you are also experiencing a surge, so you can feel something is wrong.

    Hows the truck run if you disconnect the O2 sensor and drive around?

    A vacuum leak is extra air that the O2 sensor see's as lean and adds fuel, even though it is not needed....

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  9. #9
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    Quote Originally Posted by EagleMark View Post
    GM service manual says between 9-13 PSI!
    Yes it will run between 9-13 PSI.
    Most stock trucks I have checked over the years are 12. I can tell you from tuning that even a bone stock truck runs so much better at 13 PSI. At 10 PSI the BLMs are very high...

    Have you checked voltage AT fuel pump? Ground at frame off fuel pump? Low voltage at pump = low pressure. But your saying that disconnecting the altenator makes BLM 128 which is better? Makes no sense? If you can do this again when looking at data see if the data shows it is still in Closed Loop! If not in closed loop the BLM will be 128... usually...

    I'm only guessing you have no error codes set? As that would be first thing to check and some how you are seeing BLM data.

    When you see the INT/Short Term Fuel Trim go red, it is just the program warning you the numbers are getting high. For the BLM/Long Term Fuel Trim 155 is still within boundaries of the ECM adjustment to fuel, IIRC the max BLM in ASDU is 172. So really not a big thing and if you were not a GearHead you would never know. But you are also experiencing a surge, so you can feel something is wrong.

    Hows the truck run if you disconnect the O2 sensor and drive around?

    A vacuum leak is extra air that the O2 sensor see's as lean and adds fuel, even though it is not needed....
    Thanks EagleMark, I have no error codes. I did move the ground as it was about to break to another spot on the frame. I will check your suggestions. Thanks GS

  10. #10
    Fuel Injected! steveo's Avatar
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    hey.. so wait a minute here

    if you disconnect the alternator and it runs better, and your BLMs become correct, the first place you need to jump is that it could be but a bad rectifier and/or regulator causing fluctuations in voltage, which totally screws everything.

    questions:

    - what happens if you say run jumper cables from another running vehicle, running off its alternator, while yours is disconnected?
    - is this an internally regulated alternator, or external? are you sure?
    - is your alternator bracket painted? are the bolts coated?
    - do you perhaps have an oscilliscope or a friend that owns one....?

    afaik any gm ecm should operate correctly from probably 10.5 volts to 15 volts. just because the voltage is ok on a dc multimeter doesn't mean it's clean enough.

  11. #11
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    Alternator

    Quote Originally Posted by steveo View Post
    hey.. so wait a minute here

    if you disconnect the alternator and it runs better, and your BLMs become correct, the first place you need to jump is that it could be but a bad rectifier and/or regulator causing fluctuations in voltage, which totally screws everything.

    questions:

    - what happens if you say run jumper cables from another running vehicle, running off its alternator, while yours is disconnected?
    - is this an internally regulated alternator, or external? are you sure?
    - is your alternator bracket painted? are the bolts coated?
    - do you perhaps have an oscilliscope or a friend that owns one....?

    afaik any gm ecm should operate correctly from probably 10.5 volts to 15 volts. just because the voltage is ok on a dc multimeter doesn't mean it's clean enough.
    I thought this too! The alternator on the truck was original and had 180,00 miles on it. So I bought a rebuilt alternator from NAPA which is a single wire internal regulator alternator. The bracket is non painted. Still same problem. So I decided to eliminate the wiring. I hooked the output wire directly to the postive post of the battery. I disconnected the single excite wire (brown wire) and went directly to the postive post of the battery. I then ran a ground wire directly from the alternator case to the negative post of the battery. Same problem. The motor will idle but not smoothly and it surges badly above idle. When all this started (truck would not crank had to use starting fluid) then would run, I went to the fuel pump checked pressure and it was 10# at the TBI. So I decided to put in a new fuel pump ( a new AC DELCO) this pump showed a little more pressure 11#. Yes I was smart enough to cut a trap door in the bed so I won't have to drop that 36 Gal tank again. My friend says why don't you just get another truck, well I can't afford another truck, I burn wood and use the truck in the woods, I am the 2nd owner had this truck 20yrs, it's been a good one, and frankly I am not going to let this beat me!!! G.S.

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    Coolant temp?

    Quote Originally Posted by rudder2fly View Post
    I thought this too! The alternator on the truck was original and had 180,00 miles on it. So I bought a rebuilt alternator from NAPA which is a single wire internal regulator alternator. The bracket is non painted. Still same problem. So I decided to eliminate the wiring. I hooked the output wire directly to the postive post of the battery. I disconnected the single excite wire (brown wire) and went directly to the postive post of the battery. I then ran a ground wire directly from the alternator case to the negative post of the battery. Same problem. The motor will idle but not smoothly and it surges badly above idle. When all this started (truck would not crank had to use starting fluid) then would run, I went to the fuel pump checked pressure and it was 10# at the TBI. So I decided to put in a new fuel pump ( a new AC DELCO) this pump showed a little more pressure 11#. Yes I was smart enough to cut a trap door in the bed so I won't have to drop that 36 Gal tank again. My friend says why don't you just get another truck, well I can't afford another truck, I burn wood and use the truck in the woods, I am the 2nd owner had this truck 20yrs, it's been a good one, and frankly I am not going to let this beat me!!! G.S.
    Outside temp was a 45deg when I started the truck. Alternator chg 14.3v coolant #215C open loop. Is this correct? INT-BLM numbers at 128. Oxy at 698, eng spd 625,MAP 2.65, IAC 145. Prom ID is 24F5. The coolant at operating temp was 61C. So the number went from 215 to 61? That looks backwards to me? I don't know yet how to put this chart up but I will give you the numbers and maybe you experts can put a chart to them. Engine hot; 1.18, 0, 2000rpm,61, 1.63, 143, 172, 800to100,140to56,14.1v, 83, learn control engaged, tcc unlocked,close loop. Here are the numbers with the alternator not charging; 1.12, 0, 2125rpm, 61, .76, 132, 147, 800to100, 100to20, 11,5v, 13, LCE, TCC UL, closed loop. I want to explain while the truck will run at 12volts or less it does not run perfect. It does not surge, will accelerate lite throttle or heavy throttle, but is a little rough at idle and the idle is up at 1500-1600rpms. The idle will drop back to 1000rpms in neutral in say 8 seconds. Its hard to look at this screen and drive too!! The oxy numbers are all over the place, they do not steady out with a steady throttle. So still trying to figure this program. GS.

  13. #13
    Fuel Injected!
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    Do you know how to make a log?

    At the top of TunerPro, there are some buttons that look like regular buttons on a cassette player for example. Once TunerPro is connected to the ECM, you can then make a log. When you are ready to stop the log, press the stop button and a window will open up and you can select the name and where to save this file. It will be an xdl file.

    You can name it whatever you want. Once you get that done, you can add it as an attachment here by selecting the "go advanced" option, then select the "manage attachments", then select the file and upload it.

    As far as your problem with the alternator, I could not tell you what my opinion is about it, other than possibly a ground broken somewhere allowing regulator noise to affect the ECM, but this is merely a guess.

  14. #14
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    Log recording

    Quote Originally Posted by damanx View Post
    Do you know how to make a log?

    At the top of TunerPro, there are some buttons that look like regular buttons on a cassette player for example. Once TunerPro is connected to the ECM, you can then make a log. When you are ready to stop the log, press the stop button and a window will open up and you can select the name and where to save this file. It will be an xdl file.

    You can name it whatever you want. Once you get that done, you can add it as an attachment here by selecting the "go advanced" option, then select the "manage attachments", then select the file and upload it.

    As far as your problem with the alternator, I could not tell you what my opinion is about it, other than possibly a ground broken somewhere allowing regulator noise to affect the ECM, but this is merely a guess.
    Well I hope the file is here! GS.
    Attached Files Attached Files

  15. #15
    Fuel Injected!
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    Does this log have you connecting and disconnecting the alternator while it's recording?

    Just a quick run through that log, and something might be wrong with my tuner pro, but your spark advance looks like it's jumping all over the place on it's own.

    Also noticed a MALF code 15 for Coolant Sensor Low.
    Last edited by damanx; 11-22-2013 at 01:27 PM.

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