BLM- Long term fuel trim?

[EagleMark]

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.

[rudder2fly]

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

[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!

[rudder2fly]

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.

[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....

[rudder2fly]

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

[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.

[84Elky]

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.

[ony]

bad ecm ?

[rudder2fly]

bad ecm ?

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.

[ony]

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.

[rudder2fly]

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.truck3.xdltruck4.xdl

[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?