I bought a program from PCMforless for a buddies 95 Z and later bought tunercat so that I can tweak it a little.
The program has about 35 or 36 degrees of timing but datamaster is showing 39 degrees.
Why is this?
Is there a way to set base timing on an LT1?
Do we need to do this to his car?
Any ideas?

 

timing is completely computer controlled. datamaster shows 39 degrees because above 75% throttle the car goes into power enrichment (PE) mode. it gives it a bit more timing and plays with fuel a tad.

 

I understand how the PE tables work, but I've never heard anything about the ECM adding timing above what is input in the Main Spark Advance vs. RPM vs. MAP and the Extended Spark Advance vs. RPM vs. MAP.
Why does it do this?
If this is the case, then how much timing does it add, and where is it adjustable or can I turn it off so that the timing is based on the tables I mentioned above?

Thanks.

 

There's always about 4 degrees of timing that nobody on the LT1_Edit mailing list has been able to explain. Everybody just knows it's going to be there and accounts for it.

[This message has been edited by 95ImpalaSS (edited July 19, 2002).]

 

Really?
That's strange.
Thanks.

 

On Allen Woolley's new blown 383 today we lost 10-11 degrees between the LT1Edit program and Datamaster. The program input called for 33 degrees at 40-42 kPA and 900 rpm. Datamaster showed 22/23. Now I knew of the 3-4 degrees, but 10/11??

And we were playing with the %PE tables extensively to get it closer to stoich. Didn't know of any timing changes there.

BTW, Allen has a SmartSpark but it was unplugged.

Perry

 

Dan,

Nobody could/would answer me either, so I was forced to figure out what was happening by looking at logs. Something like: 3000-4000 2 degrees; 4000-5000 3 degrees, 5000+ 4 degrees. There isn't a table exposed in the editors to control this.

However, the "benefit" is that your timing tables look a lot "flatter" up top since normally you would want to advance timing as RPM increases (less time to burn, so light it up sooner).

Perry,

At idle, the computer adjusts timing up/down, presumably to control engine speed (along with the IAC valve). Again, this is not something I've seen documented, just observed by extensive logging.

 

There are at least two tables that make up the timing. The first is Load vs. RPM table. You find the right value (it interpolates between cells if it needs to), then goes to the Temp vs. Load table to get the coolant temp adjustment. Add these two values together and you should be pretty close except for the 4 degrees of mystery timing.

 

I think the latest finger pointed to the mysterious 4 degrees being injected buy the Opti's configuration. I don't know, but I think I've seen that reasoning somewhere.

 

This is strange too....I was looking at a friends program in his 93 today and it shows a total timing of about 32 degrees and datamaster shows 28-29 degreees.
First car had more timing than what was shown in the tables and the 93 has less timing.
I don't get this. I suppose it's just one of those things that you have to screw with and believe what datamaster is telling me is the real amount of timing advance.

 

Which table was calling for 33deg advance at idle? You have to use the "0% TPP" table, not the main table, at idle.



------------------
Fred
94 Formula A3: 381/TH400/N2O

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11.513@115.59 on motor; 11.162@127.67, 1.643 60' on a 125-shot. Going with a 275-shot this year

 

OK, I've found a table in TunerCat that might have something to do with this.
It is Minimum Spark Advance vs. RPM.
In the help file it describes this table as "Table of minimum spark values that may be applied as a function of current engine RPM."

The values are as follows:
0......0
400....0
800.... 0
1200... 0
1600... 0
2000... 0
2400... 0
2800... 0
3200... 0
3600... 0
4000... 0
4400... 1.25
4800... 1.88
5200... 2.50
5600... 2.88
6000... 2.88
6400... 2.88

Do you guys think that these values are added to the main spark tables?
Should I try zeroing them and see what happens?

 

On tunercat there is a spark correction table vs map vs temp...

 

I've thought of that....but the temp has to be 219* or over and it will take out 3*.
I guess I could try zeroing that and see what happens.

 

Hmmm....I burned a new chip for this car tonight and now with the timing set for 34* we get...guess what...34*.
No idea why.
Now I just have to figure out why it has split blm's at idle after changing from 30 to 42lb injectors.