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Discussion Starter · #1 · (Edited)
Before i pick up a few more performance parts, i'd like to solve a low blm problem. After warming up, the car pegs the lowest BL the chip will read.

Here's what the scanmaster says after the car is warmed up, fuel pressure set at 41lb line off (could lower, but they still bottom out):

02: 100-700 bouncing (820's at WOT)
AF: 06
L8: 42
Bat: 13.8
Int: 129
BL: 105
Clt: 178
Ats: 98
Tps: .46
RPM: 825
Iac: 19
Mal: 00

Here's some weird things about this condition and what i've discovered so far
1) the car seems to run fine, pulls good and doesn't stumble everywhere
2) tried a Reds 93 chip, BLM's hit 90 (lowest my caspers chip reads is 105)
3) initial startup BLM's are at 115, only once the car is warmed up will it go down to 105
4) tried a screenless MAF (i have one screen), which works fine, but it didnt like my car, ran like junk, almost stalling in idle
5) BL #'s move around under throttle, reach 120's at part throttle and 130's+ under acceleration, normal i think?

What usually causes BLM #'s to just bottom out once warmed up? What should i be looking to replace in order to fix this problem?

Sorry about writing a novel, but i thought i'd give all necessary info,
Joe

MODS:
Stock Turbo/IC/Conv.:.Scanmaster 2.0.:.Cotton's 93 Octane Chip, 17#.:.42.5lb injectors.:.AFPR.:. Hotwired Walbro 340 Hotwire.:.Adj Wastegate.:.3" Solid MAF pipe.:.K&N.:.Hooker 2.5" Exhaust.:.3" ATR DP w/ dump.:.LT1 Valve Springs.:.16" Polished TTII's
 

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First, just because the blms are at 105, it does not really mean anything is wrong. 105 is still within the compensation range of the ecm so it means that the ecm is seeing what it perceives to be a rich condition at idle and is correcting it.

Secondly, it does not mean that it sees the same condition in all cells of the blm matrix either.

What do the blms read at cruise?

If you are not familar with how blms work, this is a very good explanation.

http://www.gnttype.org/techarea/faq/BLMINT.html

I did not see mention of injectors....injectors have to be matched to the chip...and sometimes the burner does not precisely adjust them vs the chip other than to make sure they are within compensation range. Also, the type of intake, etc., can affect blms.
 

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Discussion Starter · #3 ·
Steve,

Thanks for the response, i understand that 105 is not the worst BLM situation to be in, however, if you noticed one of my numbered points, i mentioned that with a chip that will allow the BLM to hit 90 (the lowest # possible, i believe) my car will have it happen. This happened with a Reds 93-octane chip for 009 (42.5 lb/hr) injectors. My mods list has my injectors. My Caspers chip, issued from Cotton's Performance here in MA, is supposed to be for these injectors as well.

The scanmaster shows BL#'s rising under throttle, 2000 RPM will bring them up into the 120 range and then heavier (3500 RPM, acceleration) will bring them up to 130's. I put this as one of my numbered "discoveries" because i'm not sure if thats normal or not? Is it supposed to be 128 static, or just at idle?

Thanks for the response,
Joe
 

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as per the link I provided, 128 is merely the center of the ecm's ability to correct. The car will run exactly the same at any given point whether the blm is 105, 128, or 138.

Red's chips are notoriously rich at idle....therefore most of them show very low blms at that point. I suspect they are crudely programmed. On the other hand, as long as they are within the correctable range of the ecm...it does not make a difference as the ecm corrects for the overrichness and all you see is the blm number showing the ecm is correcting.

Now, if the ecm was showing 90, you would not know if the ecm was fully correcting for the over richness, or not...because it would be at it's limit and might need to go even more.

Many say that a chip that matches the injectors very well will usually have blms +/-10 from 128. That way it has a lot of correctional range in either direction in case of extreme conditions.

I have never seen conditions, particularly at idle, that would worry me if I had 105 in one cell of the matrix. It's one of those things that people fixate on without any real cause for the most part. :)

BTW, 009s have a bump in the idle/off idle part of the flow curve which require some custom tweaking to get them dead on. Red does not seem to do this tweaking, but, the ecm fixes it anyway.
 

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Lots of chip guys, really don't spend the time to actually learn what they're adjusting. All they see is the inj size, and then fudge that, rather then delve into PW vs Battery Voltage correction. Hence at the shorter PWs the BLs are skewed.

The PW vs Battery correction is how the tuner accounts for the injector's opening delay. So while .4 msec isn't much, at a 2 msec., it's alot more meaningful then at say 4 msec or more.

Try getting a few chips from different vendors, say a Commander from Fullthrottle, or one of the TurboTweaks, from Eric Marshal.
 

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Discussion Starter · #6 ·
Steve,

Thanks for two quick, thorough explanations to my problem. I guess as long as the BL #'s arn't hugely skewed from 128, it isn't that big of a deal. I mean, the car does seem to run pretty good. I'm very interested in trying a TT chip from Eric, i've heard great things. I also heard the lowest his chips will read for a BLM is 110, which would put me even closer to that elusive 128!

Does anyone think it would be worth trying another 02 sensor and/or another good MAF? Or am i good to throw in my dutt neck and rjc powerplate this week :headbang: haha

Doc - what is PW, and i'm not really sure i understand the shorthand in ur post...

Thanks guys
Joe
 

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spoolinupgn said:
Does anyone think it would be worth trying another 02 sensor and/or another good MAF? Or am i good to throw in my dutt neck and rjc powerplate this week :headbang: haha

Doc - what is PW, and i'm not really sure i understand the shorthand in ur post...
If you have CC (cross counts), from the O2 sensor, then it's working. They're just a switching sensor, meaning rich or lean..

PW = Pulse Width. Injector Pulse Width in this discussion.
 

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As I said, the change in blms won't make a difference. :) and, once you are off idle, you are very close to 128, anyway. :)

You will find more benefit in the TT chip from all the tweaks that go with a modern chip with regard to programability, etc, than from any change in the blms.

Just an improved chip in all aspects. :)
 
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