"bias value for coolant compensation spark advance table"

I recently had a issue with cold startup running poorly. I thought it may be timing related so I adjusted the value in the coolant comp bias SA. Changed it from 9.84 to 24.61 which helped out the cold start issue but now it seems my top end runs poorly when warmed up. I don't think I understand what this value does or what it may effect when warm?
What did I do?

 

By changing the coolant comp bias from 9.84 to 24.61, it removed a bunch of timing.

However, not all is lost. You did find out that during cold starts it wants less timing.

Change the CTS comp bias back to 9.84, and lower the cold values in the coolant SA compensation table.

The bias value allows another table to remove timing (the CTS & IAT/CTS tables are like this). With the CTS Bias at 9.84, and entry of 9.84 in the CTS comp table does not change the timing. Basically, the bias is subtracted from the table values.

So if the CTS comp table has 19.84 deg at at location, that adds 10 deg of timing (19.84 - 9.84 = 10).

If the CTS comp table has 5.84 deg at at location, that subtracts 4 deg of timing (5.84 - 9.84 = -4).

RBob.

 

Thanks for the reply.......So I removed timing at all temps not just when cold?
I'll have to dive in and try to digest this info some more.

 

heres how the EBL calculates the final spark advance the engine actually sees:

total spark advance = main SA table + (coolant comp value - coolant comp bias) + (IAT comp value - IAT comp bias)


yes, by changing the bias you effected the entire range of temperatures. The reason for this is these computers cant comprehend negative numbers. We get around this by adding the bias. Without the bias, the table could only add timing, not remove it, because you cant have a negative value in the table. With the bias, any value on the coolant comp table that is LESS than the bias results in timing being removed, and any value above the bias results in that much timing being added.

 

This is great info, thanks. Having it explaned that way makes much more sence to me. I guess the only thing I don't understand is that the table "SA coolant comp spark advance" only goes as high as 116 degrees. I assume that's farenheight? How does this effect the values above 116 or does it just use the highest value for everything above 116?

 

It is in degrees C. Note that all of the ECU/XDF temperature scales are in C.

You are correct about reaching the end of a table. Once over the highest value it uses the last row of the table. So at 130 C the 116 C row is used.

RBob.

 

Thanks again.

 

OK here's what I did, tell me if I'm crazy...
It seems that what I'm trying to do is remove about 15 degrees timing at low temps and blend that up to zero removed as it approaches warm up temp. If I were to change the bias back to 9.84 I wouldn't have enough room to remove 15 degrees from the table without going into negative numbers. What I did was leave the bias at 24.61 and added 15 to all of the values in the coolant comp spark advance table. This should have brought me back to where I started? I then took timing out of the values by row starting with 15 degrees at the coldest temps and blended up to zero removed at about 68 C.....
Now after doing all of this I find that the lowest table values are greater than 15 so I subtracted 15 from the whole table then subtracted 15 from the bias (back to 9.84). Clear as mud?
If it seems crazy I will find out tomorrow when I get a chance to try it out.

 

Works great.

 

Thats how it's done