Do the tables in $8D at $4CF and $4D8 work together? I remember there are two tables in $42 that get multiplied, then the product of that gets divided by 256 to get a value that the INT adjusts by.

I had these two tables set so the ECM could not adjust by more than 3 at a time at any airflow or RPM (thanks to RBob).

I would like to do the same thing here to stabilize my idle. The INT swings up and down and the idle fluctuates by 100 or so RPM.

 

From what I'm seeing what you said "seems" to be correct but I can't follow where they are used together. Only see them looked up individually. I must be missing something there.
The 4CF table is all set for no reduction and may make a nice difference for you at the lower flows.
I'd like to know if that does help with that problem if you have tried it.
Another thing I see is there is a delay timer with "zero" as the default for slowing down the INT reaction when in idle.
The setting for the timer is at $849A (in AUJP)
Might experiment with a small delay time there and see if it makes it a little more stable. Could have the opposite reaction by inducing too much delay and increasing the oscilations. SP?
Jp

 

I added 2 sec of delay in the value @ $849A. It smoothed things out some.

I find it interesting that there isn't more information about this. I had to get my van passed an IM240 emissions test yesterday and it made me seriously reconsider my tune. My HC and NOx were twice the limit. This was the first time any of my project cars had failed to "fast pass".

At that point I needed to lean out the closed loop fueling but was guessing when it came to which table to modify. With the 747 it would have been a no brainer for me. There are 3 tables; low, medium and high O2 voltages to set where "128 happens". On my 730 I guessed and adjusted the tables @ $84A2 and $84AB. I lowered all the values.

I thought that this would have been common knowledge, and that I was a noob and couldn't find them because they're named something else. I really don't see how to tune this engine without knowing where those important O2 tables are or what they do.

 

High NOx typically means lean, and possibly too much timing (lean is the prominant source when working with a cat and reading post cat data). High HC does not necessarily mean rich. It gets higher when too lean as well. High HC typically represents misfire, if CO is low at the same time. That could be lean misfire/incomplete burn. The limits on the test usually are lax enough to know that if it fails HC that bad, it's probably a misfire.

EGR would also help NOx and HC, but mainly NOx.

 

So I take it the BLMs were looking good but your whole scheme was off from where your O2 was reading causing the high emmisions. Maybe you got a flaky O2 sensor in there or it just has an offset?
Seems odd that you needed to go there to get the results needed, I don't see that you are running anything special as far as the cam goes. Would have thought the VE or SA could fix it.
Nice to know that that delay can have an effect in idle.
Have you looked at the possibility of either VE table or SA table has a large difference in values between two adjacent cells. The Idle surging might be just the traversing between cells with too much variance.
Something to look at anyway.
Jp

 

I may try a new O2 sensor. In all the searches I've done on this topic I found a post where RBob gave a specific part number for an ACD O2 sensor. I might order one at work on Monday.

I have the VE and SA cells around idle flattened out. It helps a bit, but the most notable difference came from the INT delay at idle and the idle deadband value.

 

AFS 20 is the stock one wire sensor , AFS-74 is the heated stock type delco sensor.

Read Rbob's article in the stickies above for the 02 proportional gains on the TBI setups.

The $8D code is nearly identical in function, but I did learn the ANHT hack is flawed in regards to the proportional gains stuff.

It can make a difference.

WE also compared vette ANXT to AUJP and ANJF and found the vette has much much lower gain settings for the 02

later
Jeremy

 

Could you share the location of these tables? I haven't found any that look identical to the 747 tables. I read the post about the idle O2 stuff, but I was looking for the tables that determine "stoich" at part throttle.