Low BLM's - what to check next?

[Victory]

I have a situation where my BLM's are consistently low (~114-116). After searching and reading (and noticing there are a lot more issues & solutions regarding High BLM's), I learned that lowering fuel pressure is one of the first troubleshooting steps. I lowered FP from 42 line off to 40 and my BLM's did raise to 122 within a couple of minutes. I took the car for a 10 minute drive came back and lo and behold the ECU was still making corrections as my BLM's were back at 114.

I tried lowering the FP some more to see what would happen. As one would expect, the car started stumbling and the idle got rougher as I went deeper into the 30's (all line-off). At this point, I raised the FP back to 42 (line-off) as per Turbo Tweak Chip recommendations and went for a drive. Once I came back, I took a look at the Scanmaster and again at idle the BLM's were at 114 or so. I came back here and searched some more, but like I stated there aren't too many low BLM threads (not too mention searching for "BLM" releated threads is a pain in the ass using the search engine).

What should I look to next? Other than some richness smell (I am running without a CAT so some rich-like smell is to be expected) and "bad" gas mileage (about 15mph highway driving over the last three tankfuls) the car seems to be running relatively well- knock wood. But I'm ready to tackle this - if it is an actual problem. Is this a MAF prob? O2 sensor?

My Scanmaster readings at a warm idle (spending 10 seconds at each setting) were:

O2 780-824
AF 06
L8 40-46
Bat 14.4
Int 128
Blm 115
Ats 60
r 825-875
tps .42
Iac 23
cc 207

As my sig states I am running alky (@ 25lbs) and a corresponding Turbo Tweak Alky chip.

Thanks for reading!

 

[TurboDave]

Please don't take this wrong, but..... I'm still wondering why, with today's chip technology, anyone would still be fooling around changing fuel pressure trying to correct possible fuel delivery issues.

Extenders, and Turbo Tweak chips have adjustments in them to add or subtract fuel as needed.

Try that.

The most obvious question would be, when did this low BLM issue start? What had changed that might possibly cause it?

 

[1fast6]

Extenders, and Turbo Tweak chips have adjustments in them to add or subtract fuel as needed.

The 5.6 chip only adjusts for WOT.
I would take a look at the MAF and O2. Maybe time for a late model MAF and translator.

 

[Victory]

The 5.6 chip only adjusts for WOT.

Yeah, I was going to state the same thing. The first place I went to were the instructions for the chip.

Is there a testing procedure or way to know if the MAF or O2 sensor is gone or is the low BLM the indicator?

I just got the car back together this fall (after it sitting for a year). It's been this way since before it was mothballed, but I had other issues to address first. I can never remember BLM's being +/- 10 from 128. It's always been low. From my reading, I've learned the MAF changes may or may not do anything because it's a crap shoot on getting a good MAF. I can change out the o2 sensor easy enough, but I'd like to have some methodology for testing (if there is one) before I start throwing parts at the car.

 

[Steve V]

Money will be well spent on a modern 3 or 3.5 maf with translator.
Does the car run rich?

Smoke?

What does the oil look like?

Hows the power?

I have 60's on both of mine and my blms are above 128...but within spec.

 

[Victory]

Money will be well spent on a modern 3 or 3.5 maf with translator.
Does the car run rich?

Smoke?

What does the oil look like?

Hows the power?

I have 60's on both of mine and my blms are above 128...but within spec.

Yes.
No.
Oil looked normal the last time I dropped it.
Power seems fine.

Can the MAF be cleaned to see if it makes a difference? With what?

 

[Steve V]

You can clean it with electrical cleaner..probably won't help.

If it was way rich your oil would smell like gas. No cat will smell a bit rich at idle. TT chips idle open loop at idle ..smoother..but richer than oem chip.

You can find another maf to try or try to borrow someone's tranlator and modern maf set up.

If it was my car I would not be worrying about the blms(116ish),they are well within the fueling corrections of the ecm. Unless the car doesn't run right.

 

[1fast6]

If it was my car I would not be worrying about the blms(116ish),they are well within the fueling corrections of the ecm. Unless the car doesn't run right.

X2. we worry to much about the blm # at idle. How do they look cruising around town?
My blm's are about 118 at idle but the car runs great and blms around town are 122.

 

[Victory]

BLM's get up into the 120's driving around. I'll keep an eye on them for here on out. If I get any of the other symptoms (i.e. foul smelling oil, loss of power, smoke, etc) mentioned in this thread I'll know to look at the MAF and/or O2 sensor.

I guess my Scanmaster #'s look ok otherwise.

Thanks guys!

 

[Dabigguy]

Maybe a stuck/dirty injector.....didn't you say the car sat for a year? Check the plugs, maybe that will tell ya something.

 

[Victory]

Maybe a stuck/dirty injector.....didn't you say the car sat for a year? Check the plugs, maybe that will tell ya something.

As soon as Jack Frost leaves the area that's next on my list.

Thanks!

 

[mikestertwo]

X2. we worry to much about the blm # at idle. How do they look cruising around town?
My blm's are about 118 at idle but the car runs great and blms around town are 122.

+1 A low BLM doesn't mean it is "running rich". It just means the computer is pulling fuel from a centerline adjustment of 128 to get the mixture correct.

 

[Steve V]

Maybe a stuck/dirty injector.....didn't you say the car sat for a year? Check the plugs, maybe that will tell ya something.

Blms would most likely be way out of wack with a stuck injector....he's -12 from ideal.

If the injectors were not flow matched,they may just flow a bit more than desired. But none the less ecm is still in control of fuel at 114-116.