Idle BLM Solid 128

[Scott_68B]

For some reason, my idle BLM (cell 0) stays at a solid 128, it doesn't vary at all. When I'm going down the road and am in cell 1 or 2, it behaves normally. Does anyone have an idea of what might be happening and a suggestion on what I might do to fix this? I'm running a 7727 with $A1 code.

Thanks!

-- Scott

[SappySE107]

Are you sure there is a problem? What does the O2 look like at idle? How about int? Have you driven it and then checked idle BLM/INT?

[Scott_68B]

Not totally sure there is a problem but nothing I do seems to cause my BLM at idle to be anything other than 128. I've attached a sample Freescan log file showing idle right after a >10 mile run with everything well warmed up.

[Guest]

If I'm not mistaken, stock $A1 setting go to open loop at idle, so BLM and INT would go to 128 at that point.

If you look at my logs I have a prefect 128/128 BLM/INT with my car. I run open loop all the time and always shows 128/128, no matter what the O2 is doing.

[SappySE107]

Probably the flag for using airflow for idle. Uncheck if its checked.

[Guest]

Probably the flag for using airflow for idle. Uncheck if its checked.

Why do you want closed loop idle?

Most guys find that using closed loop idle will experiance surging and hunting for idle.

[SappySE107]

My 3400 swap MGB swap and Fiero swap chips have none of those issues. Not much more I can say to explain. I know what I am doing, and most people do not.

[Guest]

LOL, There's a bunch of people that I've spoken to that have more experiance than you or I in tuning, and most of the time they will use and recommend open loop idle, especially for engines that have plenty of modifications.

From what I've seen most GM bins use open loop idle as well.

[Superdave]

$A1 does not use open loop idle.

As Ben said, in a stock bin it calculates BPW based on airflow, not by o2 values. usually this makes the BLM's shoot down below 110 with very little change to PW.

looking at your log, the BLM's are 128 but the integrator is moving around just fine. If it ain't broke, don't fix it.

[Guest]

As Ben said, in a stock bin it calculates BPW based on airflow, not by o2 values.

That would be the definition of "open loop" (or at least a VERY large part of it), to ignore O2 values.

[SappySE107]

It does use O2 feedback, which is why the BLM does move even though its based on airflow. You want it to be based on the VE tables however, so you can tune them. Otherwise you have to change the gm/sec values for IAC position and possibly more. I have had to deal with those values as well but only in the extreme cases.

I tune idle first. Neglecting this easy first step makes everything else more difficult. I have done it from stock 3400 to hybrids with camaro pistons, and even complete gen 3 with camaro pistons, cam, headers, larger tb, etc. All have ended up with excellent drivability, and closed loop O2 operation. The only reason I can see someone doing an open loop only, is for a car with long tube headers and no heated O2. You are just asking for problems then.

[Scott_68B]

Thanks for the feedback everyone. I do have the "airflow for idle" bit unchecked. Guess I'll ignore it...it actually doesn't idle too bad. I'll try to fine tune it using INT. Thanks again.

-- Scott

[SappySE107]

Once you have the fueling somewhat close, you can lock the BLM at 128 by setting min and max to 128, and deal with the int alone. This is much easier for me anyway. For idle, I drive around, then come to a stop and let it sit while I watch it. This way the O2 is hot and the engine is warmed up.

[Superdave]

Thanks for the feedback everyone. I do have the "airflow for idle" bit unchecked. Guess I'll ignore it...it actually doesn't idle too bad. I'll try to fine tune it using INT. Thanks again.

-- Scott

From the looks of your datalog i wouldn't even mess with it. it's completely normal for the BLM and INT to move around. Yours is dialed in very well.

[torq455]

yeah, then the barometer changes and it gets colder, and it needs tuning again. my point is you can be too anal about the numbers. if BLM is 128 under most or all conditions, you should be very happy. hell, even if you had an idle BLM of 125 and INT of 130, that's still pretty close. one point either BLM or INT is a very small change in fueling. it's hard to not to tune to perfection, but close is just fine, and the ECM will take it from there.