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ECM Constants

Old 03-09-2006, 01:53 PM
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re: ECM Constants

Wow, I've been stickied.
Guys, if anyone catches anything that needs to be changed/added/updated in my original post let me know. I've been out of the LT1 scene for a little while and I haven't been keeping up with it at all.

I'd love to see some "articles" get written on tuning part throttle fueling (ve and maf), spark, and then wot tuning and added as stickies as well. Also, any of the idle tuning required for large cams would be helpful as it seems the same questions get asked here over and over again as new "tuners" jump onto the board.
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Old 03-09-2006, 02:34 PM
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re: ECM Constants

This is only going to work as a "tuning" info source if we DO NOT start adding in questions about topics that are not directly PCM related.... e.g. "O2 sensors". That should have been posted as a separate topic, not in the PCM Constants thread.
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Old 03-21-2006, 01:38 AM
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re: ECM Constants

BLM Cell Map Boundary Hysteresis and BLM Cell RPM Boundary Hysteresis:
If anyone knows what these values do please let me know.
I'm going to take a crack at this

The BLM table has BLM boundaries for both RPM and MAP. These boundaries determine where on the gride (which BLM Cell) your sitting at.
Stock BLM Cell MAP Bounadary is: Low 32, Mid 50, High 80.
Stock Cell RPM boundary is: Low 700, Mid 1200, High 2000.

Suppose though your crusing right around 1200 RPM and going slightly above and below it... so suppose your doing say 1175, 1200, 1225, 1200, 1175, 1200 etc. You don't want the computer constantly switching boundaries. These two hystersis settings come into play here. in order for you to be "IN" one of these cells you must leave another cell by an amount over the hysterisis value. For either the MAP or RPM. This is used similar to fan hysterisis - you don't want your fans switching on and off rapidly as your engine temp goes above and below a certain value all the time, so you give it a hysterisis value of a few degrees celcius.

I like to think of hysteris as a rubber membrane preventing something from passing from one side to the other. The thickness would represent the value of hysterisis. Push not too hard, and it may move to the other side, but not pass the membrane and snap back. Push harder and itll pass through to the other side. It cant come back either unless it pushes hard enough to come back The thicker it is, the harder it is to pass through to the other side.

The MAP values work the same way as RPM, just in kilopascals. (2kpa is default)

Last edited by TobyZ28; 03-21-2006 at 01:40 AM.
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Old 04-02-2006, 12:59 PM
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re: ECM Constants

Re: VSS Diagnostic Enable Minimum RPM

You are correct...we fixed my OBD1 high stall/limp mode problem by raising this value to 3600 rpms (I have a 3000rpm stall converter)...before that, any good launch...say better than a 1.9x 60' time would put my tranny into limp mode. - JM.
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Old 06-30-2006, 09:21 AM
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re: ECM Constants

Glad it worked for you Josh!
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Old 07-01-2006, 08:57 AM
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re: ECM Constants

EXCELLENT info. THANX. i would love to see more of this !!!

how about "ECM Tables" !!!!!!!!!!!!!!!!!!!
as i am learning Tunercat.
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Old 08-07-2006, 01:40 PM
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re: ECM Constants

Originally Posted by V-2 SQ Jes
EXCELLENT info. THANX. i would love to see more of this !!!

how about "ECM Tables" !!!!!!!!!!!!!!!!!!!
as i am learning Tunercat.

i would like this also, am learning also.
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Old 09-24-2007, 10:16 PM
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how do I disable the Charcoal canister purge switch in Cat's tuner
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Old 03-28-2008, 11:09 PM
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ok I have been trying to get this formula to work for my lucus 42 injectors (injector flow rate) , rated at 43.5 psi, running stock pressure of 43.5. I must be doing something wrong my #'s are not coming out right? and help please
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Old 10-30-2010, 01:52 PM
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Re: VSS Diagnostic Enable Minimum RPM

Which tuning software has this feature?

I've been out of the loop and think the last time I updated my LT1 edit software was
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Old 06-09-2012, 07:02 AM
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re: ECM Constants

I just installed rebuilt shortblock with improved flowing heads and exhaust.
I notice my AF/R has leaned about 1 point everywhere under WOT/PE.
I'd rather run safe/rich during break in.

Widebad AFR gauge bounces 14.2-15.8 at all speeds/throttle positions until I jab throttle into PE then AF/R runs right with my % change to air fuel at mph at WOT set points.

Is there a constant table I can tweak to raise fuel to air in closed loop all except PE/WOT?
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Old 07-20-2012, 08:20 AM
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re: ECM Constants

I'm pretty sure that 14.7 is hard-coded into the firmware.
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Old 07-20-2012, 04:14 PM
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re: ECM Constants

Kevin, have you ever toyed with "Fast O2 rich/leak Threshold Vs CL Mode" values " Tied to "CL Value Vs Air Flow" table. Read some data on it in the forums but never experimented as I don't have a wideband to measure any changes in ARF. Theoretically lowering the voltage should lean it out, raising should richen as that voltage is supposed to control BLM 128 decision point. Just thought I'd ask as you seemed to have experimented with quite a few of the parameters.
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