BLM- Long term fuel trim?

[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.

[rudder2fly]

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.

[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.

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.