BLM question

[sy2756]

I have been having some idling problems with my truck. With the base fuel pressure set to 40 psi it idles rough and the tach hunts. If I turn down the fp to 36 psi it idles fine. Using turbo link I get the following BLM data:

36 psi base, 128 at idle and 144-150 under throttle.
40 psi base, 112 to 120 at idle and 126-132 under throttle.

My truck is stock with the exception of the adjustable fuel pressure regulator.
I have checked for vacuum leaks both with starting fluid and the bike tube.
Changed cap, rotor, plugs, wires and checked the timing.
Checked fuel pressure to make sure it is holding and not leaking down.

Any ideas???

 

[jwaller]

sounds normal to me. whats the problem?

 

[sy2756]

I was under the impression that the BLM values should be about 128 all the time. Not ever having owned one of these trucks before I don't know what to consider normal for a stock truck. So based on my numbers which fp is better?

 

[kwick6]

I was under the impression that the BLM values should be about 128 all the time. Not ever having owned one of these trucks before I don't know what to consider normal for a stock truck. So based on my numbers which fp is better?

What kind of plugs/wires are you using?
What are your IAC's?

I'd say you probably have a vacuum leak, that is causing the rich condition at idle.

Check out this thread, for some more info on BLM's
http://syty.net/phpBB2/viewtopic.php?t=8778

 

[jwaller]

128 means that there is no correction factor being applied to the values set forth in the chip tables.

now I dunno about you but GM nor anybody I've seen has yet to make a chip that is 100% dead on right all the time. anything can change the fueling your truck needs at any given time. baro press, MAT, eng temp, humidity, fuel grade, altitude, OAT, and many others.

not only that those correction factors are based from a sometimes highly inaccurate O2 sensor.

take it for what it's worth. but as long as your close to 128. let it be.

make it idle good and leave it alone.

now if you want a really well tuned truck then buy a WB O2 sensor and start chipping the thing yourself and you can get it closer. but until then your locked into the issue of only being able to fix 1 or the 2 issues you have. fp has it's affects across the board. so u fix it in 1 area and muss it up in another.

 

[sy2756]

I was under the impression that the BLM values should be about 128 all the time. Not ever having owned one of these trucks before I don't know what to consider normal for a stock truck. So based on my numbers which fp is better?

What kind of plugs/wires are you using?
What are your IAC's?

I'd say you probably have a vacuum leak, that is causing the rich condition at idle.

Check out this thread, for some more info on BLM's
http://syty.net/phpBB2/viewtopic.php?t=8778

I am using Taylor wires and tried both the stock plugs and the ngks with no difference between them. I have looked high and low for a vac leak and could find none, but it doesn't mean I didn't miss it.

Thanks for the info though.

 

[smeagol]

FWIW, the BLM application in the Syty is far from ideal (even relative to the technology used in the 90s for autos). There are only TWO BLM's used, one for closed throttle, and one for open throttle. So you have a single term used to adjust long term running conditions when throttle is open... WTF is the logic behind that?

Anyways, I found 'em useless, and usually turn into a PITA during tuning. The integrator has some use, but not the BLM, IMO.