Fighting High BLM

[mtbraun]

I've been following 87chriss's post and I have exactly the same problem. Here are my scanmaster numbers after a 25 minute "easy" drive after resetting ecm:

AF-04
L8-29
Bat-13.7
INT - jumps 137-142
BL - 142 (light cruising blm is 138)
CLT - 164
ATS - 60
R-925
TPS-.42
IAC-00

I just finished having the driver's side header welded around the outside of the flange. Also had it surface planed. I am using felpro gaskets...I have read all the feedback suggesting not to use gaskets, so thinking about it. The noticeable "tick" is now gone after fixing the header.

I smoke tested it and used the hose trick and also used seafoam and can't find any other exhaust or vacuum leaks. I have 18 in. of vacuum in park at idle.

I pulled plugs and they are definitely showing lean conditions.

Fuel pressure is good at both key on/line off, and at running idle.

I am running about 100 octane which is left over from my mix when I was trying to tune. My chip is burned for 91. Could this be the problem?

 

[blackazz]

Well ill follow your thread too,I'm having the same problem with a high blm 142 use to be around 160 replaced the M.A.F with a translator,ls1 brought it down did all the same tricks too.So hope we can get this figured out.

2nd place is 1st place loser!

 

[TurboDave]

I've been following 87chriss's post and I have exactly the same problem. Here are my scanmaster numbers after a 25 minute "easy" drive after resetting ecm:

AF-04
L8-29
Bat-13.7
INT - jumps 137-142
BL - 142 (light cruising blm is 138)
CLT - 164
ATS - 60
R-925
TPS-.42
IAC-00

I just finished having the driver's side header welded around the outside of the flange. Also had it surface planed. I am using felpro gaskets...I have read all the feedback suggesting not to use gaskets, so thinking about it. The noticeable "tick" is now gone after fixing the header.

I smoke tested it and used the hose trick and also used seafoam and can't find any other exhaust or vacuum leaks. I have 18 in. of vacuum in park at idle.

I pulled plugs and they are definitely showing lean conditions.

Fuel pressure is good at both key on/line off, and at running idle.

I am running about 100 octane which is left over from my mix when I was trying to tune. My chip is burned for 91. Could this be the problem?

You have a TT chip, just add some fuel via the chips adjustable parameters.

 

[kidglok]

your iac is reading 00 at idle?

 

[mtbraun]

your iac is reading 00 at idle?

Yes, new IAC valve, been through the TPS reset procedure, been at 00 for a long time now.

 

[jdpolzin]

Open the throttle blade about 2 turns and reset your tps.

 

[Eric Stage I]

If the 100 octane was leaded, it could have killed the O2 sensor.
Since you have a Translator, you can try setting the MAF BASE to "1" (reset the ECM and let it relearn).
Also, get the IAC to read correctly. If you can't get it off 00, then there might be a vacuum leak somewhere, causing the high BLM.

 

[mtbraun]

Open the throttle blade about 2 turns and reset your tps.

Not sure what you mean by this. Are you referring to the idle adj. screw or just manually opening the throttle blade a couple times and letting it spring back?

 

[NorEaster]

Not sure what you mean by this. Are you referring to the idle adj. screw or just manually opening the throttle blade a couple times and letting it spring back?

My blm was maxed out until I replaced my injectors.

I also installed an RJC power plate at the same time so there could have been a vacuum leak in the plenum area but I doubt it as I propane checked the engine before hand.

Just a thought.

 

[TurboDave]

Open the throttle blade about 2 turns and reset your tps.

That will produce the opposite affect. turning the screw clockwise to open the throttle blade more will (under normal circumstances) momentarily increase the idle rpm and the IAC numbers will be reduced to bring the idle back to the ECM commanded value. His are already at 00. Turning the screw CCW will momentarilly reduces idle rpm, and the ECM will see this and increase the IAC numbers to compensate.
This all assumes the IAC is working normally. The screw could just be in too far.

 

[mtbraun]

That will produce the opposite affect. turning the screw clockwise to open the throttle blade more will (under normal circumstances) momentarily increase the idle rpm and the IAC numbers will be reduced to bring the idle back to the ECM commanded value. His are already at 00. Turning the screw CCW will momentarilly reduces idle rpm, and the ECM will see this and increase the IAC numbers to compensate.
This all assumes the IAC is working normally. The screw could just be in too far.

This worked. Backed out the screw a couple turns, reset the TPS and now my IAC counts are around 20. Ok, one down and one to go. I added 3% fuel and also switched the MAF Base switch to 1. Idle BLM is down to 139. Question, are the stock injectors already maxed and wont' be affected by adding fuel? Cruising BLM is around 128.

Thanks!

 

[mgmshar]

Honestly, your BLM numbers aren't too bad. If you are sure that you don't have any exhaust leaks, and your vacuum at idle is good (which it appears to be), there's not a whole lot else you can do.

When your BLM's are all high across the board (idle, light cruising, moderate acceleration), like you had at the start, there are two ways to fix it:

1. Increase fuel pressure - this will result in more fuel being delivered by the injectors at each injector pulse, which will enrichen the mixture, which will cause the ECU to respond by firing the injectors for a slightly shorter period of time to bring the mixture back to 14.7:1, which will cause the BLM's to come down. Increasing fuel pressure will cause all of the BLM's to come down, once you drive the car enough for the ECU to re-learn the new fuel pressure.
2. If your chip has the feature, adjust it to run a little bit richer (not just at idle, but across the board). This is conceptually similar to increasing fuel pressure - the ECU will learn to fire the injectors for a shorter period of time to bring the mixture back to 14.7:1, and it will lower the BLMs.

Actually, there is a third thing...

3. Try different gas. I have found that every tank of gas I put in my car causes the BLM's to move up or down a bit. I believe this is caused by the amount of oxygenates, such as ethanol, in the fuel. If "Tank A" of gas has a higher ethanol content than "Tank B", then the BLM's while running "Tank A" will be higher than "Tank B".

The whole purpose of "BLM's" is to allow the ECU to adjust for things like different fuels, small variations in fuel pressure, etc. If the world was perfect and every car/fuel was exactly the same, GM wouldn't have put all of the code for BLM's in their ECU software, right?

Now that you have your IAC, TPS, and throttle idle screw settings correct, I would go back to the Translator settings you had before you started this. If you're still worried about being at 142 to 138 (idle to light cruise), add a psi or two of fuel pressure - that should bring the readings down to around 128 (after you've driven the car for a while so the ECU can re-learn the new fuel pressure setting). When you go back and refill with 91-octane, don't be surprised if you see your BLM's change a bit again. My guess is they will go down when you run 91-octane, because I believe that 100-octane unleaded has a lot of oxygenates in it to get the octane number higher.

Good Luck,

 

[GNRick]

My blm was maxed out until I replaced my injectors.

I also installed an RJC power plate at the same time so there could have been a vacuum leak in the plenum area but I doubt it as I propane checked the engine before hand.

Just a thought.

A bad injector O ring could have been causing a vacuum leak.

 

[NorEaster]

A bad injector O ring could have been causing a vacuum leak.

I see that he has stock injectors, is that something he should be looking at?

 

[GNRick]

I see that he has stock injectors, is that something he should be looking at?

Well, if the smoke test didn't find any leaks then I'm stumped!

 

[Razor]

Stock injectors are 26 years old.. when is the last time the've been removed and cleaned/flowed?

 

[mtbraun]

Stock injectors are 26 years old.. when is the last time the've been removed and cleaned/flowed?

Uhhh, how about never! It's a two owner car, I've had for two years. I'm sure they've never been out. I was hoping to upgrade to 60's some time this summer so I might just baby it until then. Thoughts?

 

[Razor]

Uhhh, how about never! It's a two owner car, I've had for two years. I'm sure they've never been out. I was hoping to upgrade to 60's some time this summer so I might just baby it until then. Thoughts?

I think you know your next upgrade. At least with new injectors it takes that out of the equation. High BL at idle is not that big a deal as long as it doesnt hit 150+. So at 139 its still adjusting. Once it pegs 150 its dropping fuel into the cylinder. Your gas mileage will also go up with new injectors.

HTH

 

[mtbraun]

Makes sense. Thanks everyone for all the help.

 

[jdpolzin]

That will produce the opposite affect. turning the screw clockwise to open the throttle blade more will (under normal circumstances) momentarily increase the idle rpm and the IAC numbers will be reduced to bring the idle back to the ECM commanded value. His are already at 00. Turning the screw CCW will momentarilly reduces idle rpm, and the ECM will see this and increase the IAC numbers to compensate.
This all assumes the IAC is working normally. The screw could just be in too far.

Good call Dave! I was thinking totally backwards when I posted that!