Started playing with the open loop tables today. AFAICT, there are only two of them (Open Loop AFR vs CT and Open Loop AFR vs Vac). On initial startup, the engine likes to "hunt" or surge at idle speed. Once it's in closed loop, the idle changes dramatically...MUCH smoother and consistent at 750 rpm with only a minor fluctuation of about 70 rpm either way...hardly even noticeable if you weren't looking at an ALDL screen.
Anyway, I doubt this is a vacuum leak because the idle is so good once it goes into closed loop. You can actually HEAR when the ECM sets C/L.
Any suggestions? Could I disable C/L and try to tune it out like that?

 

Here's the open loop vs CTS graph. The Jeep idles at about 195F and 50-55 kPa at 750 rpm +/- 70 rpm.

 

Here's the Open Loop vs Vac graph.
Help please!!! :hail:

 

Graphs are a little hard to read. . .

I can see why the problem. Take the two graphs at the CTS & MAP points the idle is at, add them together, and it is about 16.9:1 AFR.

Closed loop is at 14.7:1.

RBob.

 

That would explain it. Thanks Rbob! So basically, I need to make sure that the open loop stuff adds up to 14.7 at the idle point. Now I can see why Grumpy says this shouldn't be done without adult supervision. If I have a 16.x:1 AFR in O/L idle, that is probably really bad for the engine. PING CITY. BUT, I am not logging or hearing any detonation out of it. Strange...

 

I like keeping my open loop stuff around 13.5 at lower maps, and 14.5ish at higher maps.

 

This kinda begs the question...How do you anticipate for the myriad ranges of MAP and CTS combinations that are possible?

 

Not sure what you mean, one table covers the coolant, and one covers the map.

 

Combine the two. Now you have a 3d table being made out of two 2D tables with what I see as many possible combinations of values.
Am I nuking this out?

 

Its not really a 3d table of course, but the easy way to think of it is::: the ecm looks at one talbe first, then after say, the given map value is found, it then searches for the given cts value.

I'm sure in newer model vehicles, the computer has a nice 3d table for open loop afr, but we have limited space in ours, so gm I guess, thought this dual 2D table would do.


Its been said before, but its too bad that were stuck with all that EGR crap, that has alot of memory tied up.

So your right in thinking that the tables will give afr's that probably are a little off, but I think that it works OK.

 

Another question from that one...which happens first...the CTS lookup or the MAP lookup? That in itself would answer a lot of questions. If you knew that, tuning O/L might take a completely different turn.
I have an idea here....before I post it, I want to see if it works. Results tomorrow or Wednesday. I have to put a comprehensive Genetics final together tomorrow morning.
Thanks for the input gents! It kinda fueled my fire.

 

The Open Loop AFR vs Coolant is a lookup done 5 times a second.
The Open Loop AFR vs. Map is a lookup done 40 times a second.

Coolant temperatures don't change too quickly.

Shouldn't see ping at idle as there is very little load on the engine.

JP did something where he combined the two tables and displayed them as a 3d table. For viewing purposes only. Should be able to hack out an Excel dohicky for this.

RBob.

 

If this is the case, why is a 15.7:1 AFR achievable on the factory APTX.bin ?

Open Loop AFR vs. Coolant @ 49.7 Deg C = 13.30
+
Open Loop AFR vs. Vacuum @ 50 Vac kpa = 2.40

 

Compared to what?

RBob.

 

Yup, the stock tables are kind of wacky but then again look at how intrusive EGR is in all of the tuning tables! For a stable idle under normal operating temps it's slightly lean but remember that in closed loop there is a bias to move the o2 window up to richen up the closed loop idle.... but why the lean AFR? Maybe it's to warm up an engine faster. Only the team in charge of tuning these motors would know... maybe I can get a hold of them through some connections I have inside GM.
It's amazing how rich they have the AFRs in open loop as well. Kind of makes you wonder if that's why the ANLU calibration has a lower VE after 80kpa (90 and 100kpa have less fuel). Very strange things.
As for the program that displays the AFR, let me compile it and work out a few bugs. The software is a tuner that does all the complicated tables and gives you actual values. I was going to wait until I finished the VE table adder (also helps visualize the tune) but the Main SA table has a LOT of compensation tables that make it hard to program. I get lost in my visual basic code when the program gets this large.