I am still having a bunch of trouble understanding the functions relating to the 16168625 ecm e6 definition. I am working on idle which I've got pretty close, but I know it's not quite there due to me not understanding the following tables and what effect changing them would have.

"Startup AFR correction (choke) Vs. coolant temp" table. I am assuming the numbers in this table are subtracted from the "open loop AFR V.s coolant Vs. map" table to richen fuel when first started. Is this correct?

"Crank BPW Vs. coolant temp" table. Determines how long injector will be energized during cranking only and below 400 rpm or so...? Uses this value until the motor is actually running? is this correct?

"IAC steps Vs. airflow" Could someone explain exactly how this table works? For example, in the table the is a % max air flow column which relates to a number of steps which can be changed. If I looked at the 31.25 value in the airflow column, there are 46 steps in relation to this value. What if I changed the 46 steps to 56 steps...what would happen...would the motor idle higher...lower?

There are also 2 other IAC tables both are flow Vs. coolant. one is for in gear and the other is for in park.

There seems to be a pile of idling stuff with this ecm and any help with how these table work would be appreciated.

Brandon

 

Hey Brandon, Im with you on the 8625, I recently got an ostrich and burn1 and have been playin with it some on my truck, but I dont have any answers to your questions on the idle stuff. It would be great if we could talk some of the guys that have some experience with this pcm into maybe writin up a little article on it to put in the stickies Anyway later and good luck, Jon

 

1) yes
2) Base Pulse Width, so there's other modifiers in use.
3) Increasing it, will initially try to hold it open more.
4) And?.
5) Yes, there is alot of idle stuff, typically that's a frequent complaint area, so the oems try to make the idle as smooth as possible. Plus the engine isn't spinning very fast, so any sort of *miss*, will seem worse then it really it.

 

Jon, your right. There isn't a ton of info on this ecm as like with the 747's. I was glad to see I'm not the only one that feels their in the dark understanding the tables and their functions using this ecm. There is however one member (and more I'm sure) who has done tons of dissembly and code on this ecm, but to be honest, that's way over my head. I would like to see something like you suggested: Maybe an article which lists each table, along with a brief description of what effect takes place when changing the values within the table.

Grumpy, your comment on number 3...You said it will initially try to hold it open more. You said "initially" which leads me to believe that eventually something else is going to take place. Will this table settle somewhere different?

I am assuming that the IAC steps Vs. airflow table is a base table used to tell the ecm how much air is flowing based on how many IAC counts, But how do I determine what that flow is and how many counts that flow should equal?

The IAC is further adjusted based on coolant temp and which gear is selected.
IAC Airflow Vs. Coolant temp. (in Drive)
IAC Airflow Vs. Coolant temp. (in P/N)

 

Brandon

 

I am running a '8625 in may car. Its the 3rd type of ECM/PCM I have run, and I found it by far the easiest to get the idle right. Most of that stuff you don't need to change. Stick with the basics, get your BLM's right in the idle area. Make sure your timing table (closed throttle) is flat in the idle area. Check that your TPS% on the datalogger is less than the TPS Idle threshold, so it is actually trying to idle.. etc..

 

I think I'm all good in the areas you mentioned although it still runs lousy at startup. The cam pulls around 11" of manifold vacume at idle. One thing I have noticed is that if it is run for a while without the battery being disconnected it runs better and better each time it is started then run. Disconnect the battery then reconnect it, and it immediately starts running rich again. It's as though the ecm is slowly correcting over time the area that is not programmed correctly. I'm lost at what to try next.

 

Your PCM is learning and correcting for miscalibrated VE tables that are rich. As the BLM values are learned, they are stored in non-volatile memory that is maintained as long as the battery is connected. Every time you disconnect the battery, you are clearing this memory then you run rich. This PCM stores seperate BLM values for the following; Idle in gear, Idle in P/N, Idle with A/C on, and then Normal BLM corrections. Get the VE tables in order, especially the near idle table, and this issue should go away. HTH

 

So, would disconnecting the battery each and every time I make a change be a good idea? It seems that If I did, It would be a very good indicator right off the bat of how close I really was so that the ecm wouldn't have to compensate as much. What are your thoughts.

 

It depends. Whenever I calibrate fuel in open loop, I always disconnect the battery by pulling the ECM fuse but when tuning in closed loop, I don't. IIWY, I would do it this way as way as it is the most accepted method unless you are disconnecting the battery for other reasons such as a a rarely driven vehicle. It is not necessary to disconnect the battery to swap the chip. Ignition off is good enough. HTH

 

There is alot of stuff pertaining to the idle since the PCM uses a full PID control loop (complicated). The IAC flow vs. cool temp tables (for in park, drive, etc) are there to provide a base number of IAC counts for the first few seconds of startup until closed loop idle becomes active.

Heres some more info. Since I cant remember anyhting, I wrote it all down. Even though its still not complete, nearly all the code pertaining to the engine is completely commented.

 

Haulin, I will do it the way you suggested from now on...Much simpler than disconnecting and reconnecting the battery each time.

Dimented24x7 Thanks for the attached zip file. I will check it out and get back with you if I have any questions...Which I'm sure I will! LOL
Also, A while back you had asked me to attach my log session so you could take a look at it and see my problem areas concerning idle. Once I get the idle as right as I think I can, I'll pass it on to you. I'm really determined though to get it as close as I possibly can first.

Thank You,
Brandon