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.

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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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.

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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.

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Originally Posted by rudder2fly

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.

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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.

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Originally Posted by EagleMark

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.

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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

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!

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Originally Posted by EagleMark

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!

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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.

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....

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Originally Posted by EagleMark

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....

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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

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.

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Originally Posted by steveo

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.

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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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Originally Posted by rudder2fly

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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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.

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.

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Originally Posted by damanx

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.

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Well I hope the file is here! GS.

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.

You can see where I disconnected the alternator it's less than 12v about half way thru the recording. Connected it's 14+ volts. I replaced the coolant sensor last nite it's a NAPA TS4052SB. My question is does the coolant sensor start a high number like 205C in open loop then drop down to 62C in closed loop? How did you read my file? All I see are all kinds of marks. Is this what is called HEX and how do I change this into letters and numbers?

I did not notice the voltage.

At the menu at the top of TunerPro, select "view", then select "toolbars" then make sure that "data acquisition" is checked.

If it is, then you should see the following icons:

A red circle target looking icon, which is a gauge. Select that and a default gauge display will show up. It will look like a digital dash.

The next icon looks like a notepad. Select that and you can see the data and numbers in line by line, (like written on a notepad per se)

Next icon is a clock. This shows info in a table based on rpm/map values.

Last is a bargraph icon. It's the data monitor where you can see things in like a line graph format.

As far as the 15 error, disconnect the battery for a few minutes and reconnect to reset the ecm.

Is the engine block ground good?

Oh, I read your file by opening it in TunerPro. That is done by using the button that looks like an "eject" button, or by selecting "acquisition" then selecting "load log file".

I forgot that I disconnected the coolant sensor while the truck was running yesterday and got that alarm. I will clear it out. It showed 250C disconnected. Is that right? The engine block ground is good. I loosened and retightened same. Thanks GS

FWIW, here’s my take after looking at the log file (have posted the log file in .xls format for viewing in Excel and rearranged some columns to aid in analysis).

Observations not in any particular order:

• TPS is not properly set nor is idle. TPS at idle shows to be 0.90v (should be less) while TPS%=46% which is way too high (should be 0%).
• Idle seems way high for a stock engine at 1000+. Properly setting idle and TPS will solve some things but that’s likely not the issue you’re seeing. At this point, not really sure what that is. Search for setting TBI idle.
• Before the alternator is “disconnected” at sample #972 (green line), things are clearly not right while it's "connected" regardless of whether in Open Loop (OL) or Closed Loop (CL):
  
  • Idle RPM rises from 600 at 62*F to 1000+ at 130*F. Not right and just backwards of what should happen. RPm should drop as temp rises. Also, this takes 7 minutes (435 engine run seconds). Not right.
  • BLM is 135 in OL before going into CL at sample #765 (blue line). Should be 128 in OL
  • After entering CL, BLM rises from 135 to 159 and stays there, while INT changes slightly for a few samples and then locks at 128. Not right.
  • Takes 15 min to go into CL. Not right.
  • KPa is in low 40’s = seems too high for a stock engine running at 1000 PRM in P/N (= no load).

With alternator “connected”, it seems fueling is being improperly managed and/or reported by the ECM.

Then when the alternator is “disconnected” at sample #972, things seem to become normal:

• After disconnection, BLMs immediately drop from 159 to believable, slightly lean values in the low 130s.
• Also, note that kPa’s drop from low 40s to mid 20’s which is more believable at 1000 no-load RPM. So RPM stays the same at approx 1000 after disconnect, but kPa’s drop to mid-high 20s with no change in load. Not possible unless ECM being affected (by the alternator wiring???)
• IAC position now seems OK at mid 40s with the idle RPM. Should be much lower, but that will be fixed by properly adjusting idle and TPS.
• Throttle tap between samples 1077 and 1099 seems normal looking at the log.
• Battery volts drop to just over 12v from over 14v at sample #972. This seems normal as it is not uncommon for single volt alternators at idle or slightly above to require a certain higher RPM (1200+) to initiate charging in excess of 12v (see: http://www.powermastermotorsports.co...rnators.html#1). So, approx 12v at 1000 RPM seems right.
• Finally, it seems that the alternator is properly hooked up after you say you disconnected it. I’d check wiring. See also above link for details + additional searches.

So bottom line, all seems normal with the alternator “disconnected”. Do a log while driving it with “alternator disconnected” and describe what occurs.

bad ecm ?

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Originally Posted by ony

bad ecm ?

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I have replaced the ECM with a rebuilt Advanced Auto Part same PROM is still being used that was installed when the truck was new and this is the 3rd ECM I have tried solving other problems none of which were solved by changing ECM's. I also bought a complete ECM 1227747 with prom AMUR on Ebay it is the latest ECM try and no help here I only saw a faster idle and a fast shift from 3dr gear into over drive mode. The seller said this would work in my truck but as I researched this PROM and it is for a 1987 truck which probably doesn't make any difference? I now am now running the Advanced Auto ECM with the ASDU Prom. I will try a run with the alternator unhooked and post the log here. G.S.

paulse with vs battery voltage, on a 288 ecm at 11.2 volts paulse with is 1.063, at 14.4 volts it is 0.984 that will change blms a lot. I don't know what it is on a 7747.

I have two logs to post. Truck3 is the motor running with the alternator not charging and Truck4 is charging. Sometime back I changed the TPS from the original because of the non start issue. This sensor was OK. They are non adjustable and the new sensor NAPA 3-1947 may be way off in adjustment. Maybe I should go back to the old sensor? G.S.Attachment 5911Attachment 5912

What kind of cable do you have? The 10k switch is on so your running in ALDL mode, which increases timing, raises idle and who knows what else. Your knock counts are going crazy driving with all that extra spark.

Have to turn that switch off and do another log.

TPS% at .90 is way to high, have to loosen it and twist it to get voltage back down. GM says .54 is perfect, I say anything under .70 does not effect it.

Not sure why a lower voltage makes BLM better/lower? Actually less voltage would be less fuel from pump and should make it worse!

WOnder if being in ALDL mode, added spark and all the knock counts is causing a misfire and giving the O2 sensor false readings? Have you ever set timing on this to 0 with bypass dis-connected as well?

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Originally Posted by EagleMark

What kind of cable do you have? The 10k switch is on so your running in ALDL mode, which increases timing, raises idle and who knows what else. Your knock counts are going crazy driving with all that extra spark.

Have to turn that switch off and do another log.

TPS% at .90 is way to high, have to loosen it and twist it to get voltage back down. GM says .54 is perfect, I say anything under .70 does not effect it.

Not sure why a lower voltage makes BLM better/lower? Actually less voltage would be less fuel from pump and should make it worse!

WOnder if being in ALDL mode, added spark and all the knock counts is causing a misfire and giving the O2 sensor false readings? Have you ever set timing on this to 0 with bypass dis-connected as well?

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I have the Moates Extreme ALDL cable set at 10k. The TPS sensor is nonadjustable! Timing is set at 2 degrees BTDC with the computer not in the loop. The engine will surge with thoughts of running right then drop back like it is dropping cyclinders when charging. Not charging runs pretty good. G.S.

Don't run 10k and get another log with charging system!

You can file the holes in TPS for more room but should not need it unless you have been adjusting the minimum air screw. You can also bend the tang on TBI behind sensor as a second choice.

at lower voltages the paules with is higher 132 to 137 blms higher voltage paulse with is lower an makes blms go up to 150 or more.

Dam your good ony! :thumbsup:

[IMG] truck5.xdl[/IMG][IMG] truck6.xdl[/IMG]

You didn't't get those files attached right, can't open them.

At bottom of reply box you will see go advanced, then under that is an attachment manager which works better for files.

Attachment 5947Attachment 5948Log- truck5 Is running at 14v with all the adjustment I could get on the TPS. About halfway I went to 12v. Log- truck6 is with the old TPS. I could not tell that the TPS had any effect on the problem other than high RPMs on idle.

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Originally Posted by rudder2fly

Attachment 5947Attachment 5948Log- truck5 Is running at 14v with all the adjustment I could get on the TPS. About halfway I went to 12v. Log- truck6 is with the old TPS. I could not tell that the TPS had any effect on the problem other than high RPMs on idle.

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I notice on Truck logs that this is not constant. It is on and off, is this normal? Would anyone have the numbers I should be seeing in these logs. I am thinking about going back to the original ESControl! The NAPA TPS was off out of the box I may just start putting all the OK used parts back on the motor? Suggestions? GS.

Well here I am July 2018. Some may be wondering what happened with this truck. I put a toggle switch to drop out the alternator so I could get the engine to pull when I needed it. Then in Dec 2017 the engine started to knock so I had a crate motor installed. I told the shop how it won't run right charging and the new motor ran the same as the old one. So as a last resort I swap in the old original TBI injectors that I had changed out in 2013 to NAPA MPF 3-18202. The truck is now running as it did when I bought it in 1993. Can someone tell what is going on with these NAPA injectors? I fought this problem for 5yrs and 2000 miles.