Trouble with idle speed in park

[srobertsfsj]

So the latest is that I did figure out why I was idling so high in pk/n. It is because of the Spark Bias - Warm parameter. I was running this at 0 when it should be set to 10. Not sure exactly why but changing it dropped my rpm from 1250 to 950.

I have not messed with park to drive steps parameter. I would say dont mess with it. I have learned to only change what is absolutely needed otherwise you could mess things up drastically.

[EagleMark]

You added 10 degrees to timing when you set warm spark bias to 0 from 10 (9.84).

[shimniok]

Digging this one back up again. :) I'm confused about the SA Warm Bias. The comments say this value is subtracted from the main SA table when warm, to permit negative values. In other words, if you set this to 10, it's basically telling the ECM that any value of 10 in the main SA is actually representing 0 deg SA. Any value below 10 is negative, and any value above 10 is positive. Right? So if that's true, then changing Warm Bias from 0 to 10 means that 10 degrees were subtracted from timing across the board when warm?

[EagleMark]

Yeah what happened to srobertsfsj ?

Your correct. But you forgot there is a cold spark bias of 20.04 in this ECM as well as Warm Spark bias which is 9.84 in SB cals and 0 in BB cals. Both Coolant Comp Spark Advance compensations are simalar. But look at a BB to SB Main Spark Advance table and you'll see BB is actual when warmed up.

We haven't even talked about Spark Latency Corrections difference between SB and BB? Spark Latency is the time it takes for EST module to process signal, although both use the same module the Latency settings are differant, neither are correct but it's there. At 6000 RPM 6 degrees difference. There are also a couple differant EST modules over the yeas, one takes out 4-5 degrees around 3000 RPM and one adds in 2 degrees. So where did you say your timing was at?

Can't use negative numbers in Main Spark Table so bias was the cure for low RPM high load areas and cold start. Good for long lasting street engines as when floored from idle spark advance can go negitive, not so good for a race application but that is not what it was made for.

You could 0 them out to end up correct. But so many other things going on look at Spark Advance Paremeters. How many now need to be changed? What have you taken away that GM thought was needed and built in? Ouch, my head hurts... since we are usually only working on final spark advance when warm just leave everything alone and look at your main spark advance table with 10 (9.84) subtracted and your real close, all other adders and subtractors work well.

If you built the 9.84 Warm Spark Bias into the mask/definition file your Main Spark Table would look correct, but what happens if someone with a BB cal uses it? There's a couple $6E masks around that one has this and one does not. Causes big issues!

Another more important issue is after adding in all the spark you can and it runs well. Have you checked to see how much more spark is added during PE? Say your up to 30 degrees advance total in Main Spark Table, now add in Spark Slope and PE and you could have 40 degrees advance actual at timing marks but you think your at 30 because of Main Spark Table, or 50 if you use a stock table and 0 out warm spark bias!

Most conversions on stock to mild engines it's all not so far out to make a difference, but when you run a built engine and are pushing max timing at WOT you could be WAY over what your shooting for.

All that said I have learned to leave most paremeters alone in each stock bin I start with. Use the Main Spark Table as a guidline. Check actual spark advance at timing marks with timing tape or dialback timing light which is hard to do at 3000 RPM and up as you need to keep RPM steady and unplug vacuum to MAP to get full advance reading. Even then it will not reflect PE spark...

"So where did you say your timing is?"

[shimniok]

*mind blown* :D

Thanks for that rundown.

Dang there's a lot going on... and that's just spark.

Yeah I see why you suggest not messing with anything you don't have to... stick to the basic stuff. I'm still trying to sort through the various threads and stuff to figure all that out.

Scott was over yesterday to help me out. We got my static timing set and did some minor tweaks with VE while idling. I'm borrowing his Autoprom so now I can start to get a feel for how to tune.

Back to topic, Scott said he figured his out but didn't remember what it was that fixed the high idle.

I have my own high idle issue (well, that's a symptom) but I will start my own thread if I can't figure out what's going on soon.

Thanks again for all the help

[srobertsfsj]

I am still here Mark! Just haven't had a lot of time to surf. I have got the timing pretty much dialed in on the Jeep but haven't been able to drive it much. Just too much going on at home.

@Michael, reading back over the thread it was the warm bias that fixed my high idle issue, along with keeping the pk/n wire disconnected.