Could somebody shed some light on this parameter. I have the idle mode flag checked under wot but the idle spark gets disabled....

 

this is the 730ecm.

 

Doesn't sound correct. Maybe the scan tool is displaying the wrong status. On the $8D mask the idle state is defined as true when the TPS% is less then a threshold (2.3%) and the vehicle speed is less then a threshold (15 mph). This is the status bit that is output via the ALDL line, and is used within the fueling routines.

Now for the idle SA control there is another TPS% threshold that is used. It is an IAC idle control threshold which is used for IAC and SA idle control.

RBob.

 

I had it reversed The idle spark is the one staying on..

 

I'll wager that it just means that the last time an idle SA correction was made it was for an idle underspeed condition.

There isn't any status bits that define whether the idle SA is active or not. The only idle SA status that is output via the ALDL is the one above (as long as I didn't miss any).

RBob.

 

Could you explain what that means. In detail. Please..

 

maybe I shouldn't have begged

 

go thru the anht hac and check thru the spark tables :-)

Can retard 5 degree and add 5 degree at idle :-)

Believe Rbob was saying that the idle dropped(rpm) or changed and the ecm added timing too compensate to correct it back to your settings

later
Jeremy

 

The thing is that my rpm at idle is not rock steady(because of the HUGE cam). Guess the ecm looks at that as an rpm error and corrects spark. Seems to be THE reason my timing jumps around at idle. I modified the main spark table to get a steady reading through aldl(for timing). It helped but you are saying it's correcting sa and using the idle speed error table,yes? If so then I just need to zero out those two tables. It's all related to the monster cam. When I'm done tuning for this cam I'll post what I learned.

The idle error thing would seem to effect most large cammed engines....

 

You got it! What can happen with the SA idle correction is that it can be too much of a change in SA. This leads to oscillations in idle speed.

I've found that a _little_ idle SA correction helps. I also tweaked in the idle SA correction MAP multiplier tables. One problem here is the range of the MAP mult tables may not cover the idle area of a hi-po engine.

It can take some staring at log files to see where to move things. Then of course trying it out.

RBob.

 

Here is a snapshot of my 406. You can see the spikes in timing. On every spike the idle spark bit displayed is "1". I will change the idle speed error tables and post the results. My bet is a rock solid idle s/a.

 

There use to be more s/a spikes and dips when I first started to tune. The main reason s/a varied was the map signal. I re-routed some vac lines and the signal improved. Then I had to go into the area (in main spark table) where my engine idles. Since the rpm varied I change the spark like this..
( I know the table as a whole is a mess. I'm waiting for the 3500rpm converter before brushing things up)

 

comments are welcome

 

With the $8D mask the idle SA should be from the closed throttle table. There is a kickdown required first, once that happens I believe the closed throttle SA table is used.

Nice graph. I'd say that the engine has the typical rolling idle. It may even be getting pushed a bit by the idle SA correction values. Can see this in the MAP value. The RPM changes are too hard to see in this particular graph.

Looking at the SA and the MAP notice how as the MAP increases (falling RPM) the SA also increases. Maybe too much as the MAP will quickly decrease (rising RPM). The ECM then responds by decreasing the idle SA and the RPMs drop back down.

I'd start out by zeroing the idle SA correction tables (just the SA ones, leave the MAP compensation tables at 255).

Then data log the idle. If it is rolling add a little SA to the too-low idle speed table. Data log again, and see if it helped.

May also need to pull a little SA from the too-high SA idle speed table too. A little at a time until the rolling subsides.

Make sure there is enough dead zone so that the idle SA correction isn't fighting.

RBob.

 

Would adjusting the idle deadband help in a situation like this?

I haven't had to tune a lumpy cam motor yet but I would think it would help from over correcting.

 

not sure what you mean...

 

FYI, the cam specs are 242/250*duration,.540/570"lift,114*lsa

The idle is good. It only changes 50rpms. It's just those darn timing spikes. I'll post the results tomorrow.

 

Ahhh, ok. I was wondering if the idle was flucuating too much and causing the KPa to change which made the SA spike.

Hopefully my logic isn't too crappy, but I'm still learning. I even picked up a '90 Formula to keep learning on... well, after I fix the intake leaks and rust

 

Yep, with what RBob said.

Is your IAC moving around while this is going on?.

The idle deadband sets how close the ecm tries to keep the actual idle speed to the commanded.
I typcially set the first couple of idle spark corrrection entries to 0. And then no more then 4d after that.

If you load up RBob's new 58 ecu file and look at a 58 bin you can see the IAC deadband settings. I just mention his since I was just looking at it. Others probably have it...

 

That's what I was wondering. But it looks fairly steady to me. I'm going to play with the idle speed error settings today. Seems like those two tables are not helping the s/a(stock settings). We'll know soon enough. Not sure I want to mess with the idle deadband though(if 8D has it). BUT the idle deadband setting could be causing this "false idle speed error"??? I say false because the idle is good. The spark advance is just not steady..

 

That was happening too. That's why I posted my main spark table. You can see how I fixed that..

 

FYI, The idle only varies 25 rpm on either side of commanded RPM. Enough to cause an idle speed error...I guess so..

 

don't understand why there is still .4* change in s/a. It's much better though....

 

Anyone want to look at my bin and help find the .4* idle (s/a)correction? I don't see how there is still correction...

 

The .4 degrees is a single bit change (0.352 °SA). Probably caused by rounding errors within the ECM math routines. IOW, nothing to worry about.

The idle does look much better. The IAC is doing a little work too. May be able to reduce that by getting a little timing correction back in.

RBob.