High BLMs, How to fix it???

[truckins10]

Ive had some good suggestions from some list members already which have helped but not completely correct my problem. My BLMS were at 148 and knock was always around 6-9KR. After installing rebuilt injectors the BLM is at 140 and KR is down to 2-4. What should I attempt to do to lower my long term memory to 128. Her is a list of what has been checked and done......
-no vacum leaks
-new oxygen sensor
-fixed exhast leaks upstream of O2 sensor
-FP set to 47psi base
-FP rises with boost

Cnat think of anything else right now, but im already running rich at idle. BLMS at idle are at 100-110, at WOT there at 140-143 like I said before. Should I be concerned about this???? Thanks ahead of time. Fern Sy#477

 

[kwick6]

Re: High BLMs, How to fix it???

Ive had some good suggestions from some list members already which have helped but not completely correct my problem. My BLMS were at 148 and knock was always around 6-9KR. After installing rebuilt injectors the BLM is at 140 and KR is down to 2-4. What should I attempt to do to lower my long term memory to 128. Her is a list of what has been checked and done......
-no vacum leaks
-new oxygen sensor
-fixed exhast leaks upstream of O2 sensor
-FP set to 47psi base
-FP rises with boost

Cnat think of anything else right now, but im already running rich at idle. BLMS at idle are at 100-110, at WOT there at 140-143 like I said before. Should I be concerned about this???? Thanks ahead of time. Fern Sy#477

what are your 02's at when WOT? You might try to lean that FP down, 1-2 psi at a time. see if you notice any change in BLM. make sure your still maintaining the 02's in the 900's at WOT. With BLM's at idle around 100-110, just means your running on the rich side. It might be something that needs to be changed in the chip to get it right though. Your kinda limited when all you can do is adjust the FP.

What mods do you have on your truck?

 

[truckins10]

Scott,
Right now at WOT O2s are .900 or more. My mod are as follows....
180 thermostat
msd coil
recent complete tuneup
AFPR
High flow fuel
intercooler mods
cone filter
20g compressor and 12cm turbine turbo

If I cut down FP a bit It'll make me run leaner(making ECM compensate more) at cruise and WOT. Thats why I didnt know what to do. Yet at idle, the ECM is compensating big time to lean out the truck. I dont know what else to check to fix this problem???

 

[kwick6]

Scott,
Right now at WOT O2s are .900 or more. My mod are as follows....
180 thermostat
msd coil
recent complete tuneup
AFPR
High flow fuel
intercooler mods
cone filter
20g compressor and 12cm turbine turbo

If I cut down FP a bit It'll make me run leaner(making ECM compensate more) at cruise and WOT. Thats why I didnt know what to do. Yet at idle, the ECM is compensating big time to lean out the truck. I dont know what else to check to fix this problem???

The ecm is already trying to compensate too much if your BLM is at 100, IMO. Thats why I was suggesting if you lower FP in small increments you might see that number get closer to 128. The closer you get it to 128, the better, because the ecm won't be trying to lean it out when you go WOT, like its doing when you see the 140.

I've been through this and its not easy finding a good spot to set FP, so that the idle, tip-in, cruise feels good and the WOT has enough fuel. Its a guessing game, until you can get your hands on a WB02 and some stuff to modify the VE tables in your chip.

I'd see if you can get the idle, cruise BLM's closer to 128, by dropping FP a bit. For me it was just messing with the FP, until I was happy with the way the truck felt, with least amount of hesistation. You could keep track of the FP's in 2 psi increments, and make notes on how the truck felt and how the data looked from the scantool, until you find the spot you like.

Also, pull your ecm-b fuse so the BLMs will re-learn when you change the FP.

 

[truckins10]

Scott I will try that.
I agree with you that if I lower the FP the idle blm should increase to 128 but, when I see 140BLM at cruise the ECM is increasing injector pulse width because it sees that things are lean. Please correct me if Im wrong. Fern Sy#477

 

[TyMeUp]

I looked at this yesterday, but held off since you are not going to like my final diagnosis. $$$

You are not wrong. The ECM is indeed correcting for a rich at idle, lean at cruise (not WOT) condition. (WOT is 'open loop' so BLM is not updated.)

Basic thought: a small amount of extra fuel at idle will cause a large BLM correction, but will be insignificant at higher RPMs. (Just the opposite of a vacuum leak.)

1) Make sure that you are not getting extra fuel into the intake from the AFPR vacuum line. (Plug the line, run at idle with a hand vacuum pump connected to the AFPR set @ 20"Hg) See if BLM changes.

2) Make sure that your new injectors are not leaking extra fuel when they are supposed to be closed. (Check engine off fuel pressure - should hold for several minutes... it's assumed that your pump check valve and AFPR don't leak.)

Next logical thought (bad thought): The only thing left that could produce the 'weird' BLMs is wrong injector calibration (less than OEM flow specs). Your high FP setting could be over compensating for this at idle, but at higher RPMs, when you need more fuel delivery, it's not enough.

If you decrease fuel pressure so that 'idle' BLM goes up, does the 'cruise' BLM also increase? That would kinda confirm this.

You didn't say what brand replacement injectors you used or where they came from. I suspect that these are a 'universal' replacement made for a large number of applications. (With many years of experience, one finds that 'universal' really means 'misfitall'.)

I would suggest that you send your originals out to be cleaned and tested. That shop in Big Rapids, Michigan seems to have original flow spec knowledge and did offer an exchange program to get you a matched set.

http://www.cruzinperformance.com/fuelinj.html

 

[sy2756]

truckins10

Did you ever get this issue resolved? My truck has a similar problem but not quite as bad. I can adjust my fp up to get in the 128 range under throttle but I run very rich at idle. If I lower it to get my idle BLM to 128 under throttle it goes way up.

 

[leroy]

FWIW, BLM's aren't a very good tuning tool. There are only 2 BLM cells. One is for open throttle. One is for closed throttle. Use the integrator for part throttle stuff. Look at O2 volts and plugs for WOT stuff.

HTH,

Jim

 

[kwick6]

If you really want to make your head hurt, read this thread...

http://syty.net/phpBB2/viewtopic.php?t=20928

You can use the BLM , integrators to tune, but probably won't see any decent results until you can modify the cells in the VE tables to watch for change in BLM.

The following info is based off of turbo buicks, as we don't have MAF sensors, but the same theory applies. Since we only have 2 BLM cells its not much help in tuning, but it can give you an idea of where your at.

BLM values are divided in to "Cells" based on MAF vs. RPM. Within each cell, there typically values from 105-150 for the BLM. Within the BLM value, there are Integrator values, typically 105-150 also.
The Integrator is adjusted based on sensor feedback (primarily the O2 sensor) to make real time adjustments for varying conditions. If the adjustments cannot be made in a BLM value, then the BLM value is either increased (add fuel) or decreased (subract fuel) to compensate.

If you reach the "corner" of an individual cell and not further adjustment is possible, the car may not run correctly and there is a problem with the calibration or a critical sensor.

It all sounds very intimidating, but really isn’t. One must keep in mind that the changes that are being made, as in the INT for example it is happening at close to 20 times per second. Think of it this way; The INT is used to “drive” the BLM number toward a value needed to maintain stoiceometric A/F ratio. As in one of the examples above, make a radical change (such as removing the fuel pressure regulator’s hose) and watch the INT do it’s thing!! The INT will jump to a high value, and hover there while the BLM starts its “march” up the scale. As the BLM approaches the value needed to get the A/F ratio corrected you’ll see the INT value heading back down toward 128. Ideally, they will both meet at 128 at about the same time. It’s really neat stuff to watch.

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