When attempting to find the best spark at idle in HP tuners, why does the idle fluctuate so much? This is using the absolute spark feature of the bi-directional controls. I had a mail order tune a couple years ago that I've modified as I went. Now I want to be able to completely start from scratch and be able to do things right. I'm learning, just got questions that come up along the way. Any help is greatly appreciated.

 

I would say because you aren't letting the engine control the timing so the natural differences from cylinder to cylinder are making it stumble?

 

Take a look at your idle overspeed and underspeed timing tables. You might have them set up to aggressivley.

 

Okay, thanks. They are set up stock as of now. How do I tune these intelligently instead of just guessing? On the fluctuation, it's like a surge I guess, so it's pretty big. I should have said surge instead. Thanks for the help!

 

Actually, the real reason the idle will fluctuate so much is because the idle timing is so far from MBT, a little chance in the positive direction will make a huge change in idle speed.

 

Not to sound stupid; but what is MBT?

 

Minimum spark advance for Best Torque

 

When I add or lower, it flucuates. How should I find the sweet spot like this? Maybe let it wait a while?

 

You'll most likely need to add. Depending on what it is already. You want to make sure the A/F is right too, as if its too rich it will cause it to not stabilize.
You can use the timing and A/F correction in the bi di controls to get it right where you want it. What are you working on? Type of car, engine, cam, etc.

 

That doesnt come into play when you're forcing it using the bi di controls.

 

That right there makes it sound like a fueling issue. I would set your timing at 27 for instance, and start leaning it out using the A/F correction in the controls.

 

I was going to say that but I am not the tuning boss.
With the absolute timing hold that is the only reality I can see.
What about the Delta timing hold? I wonder if it has any trims in it or if it is just the spark table -+ whatever you spec out.

My engine holds RPM fairly well when I hold the timing but its not a beast either!

 

Yeah, you need to use delta since it leaves the over/underspeed correctors enabled - at least it seems to in EFI Live. Then again, I do things a little backwards compared to some of the guys who posted above...

 

Okay, thanks for all the help! Where is the delta spark you guys are talking about? I don't see it in the bi directional controls. And the AFR correction is the AFR control, correct? Sorry for all the questions.

 

In order for us to help you more, we need more details. Cam, heads, etc. There are huge differences in a tune for specific setups.

 

Yep. A tune and a runlog would go a long way too.

 

Okay. Sorry about that. I would like to learn how to do this in general; but I guess if I do this on mine I can learn from there. MS3 cam, ported heads, ported fast 92-92, 85 maf, all other bolt-ons minus ewp, 92mm wet plate kit, etc. etc. Once I get this tune all sorted out, I've got a custom grind to throw in and tune and see how fast I can get. Forgot to mention 37 lbs. injectors also.

 

Here is the tune that is currently in the car. This is for the stock maf that I put back on it for now. As I said, I'm learning so be gentle.

 

SD tune it, and that will take care of alot of your problems. It looks like you reduced the 400, 800, 1200 columns, but it probably is still too rich.
Read the tutorials on SD tuning, and use your histograms. Concentrate on 4000 rpm down. Make sure the 400 column is lower than the 800 columns, when you're making your adjustments.
Fix your timing table.

 

How should I fix the timing table?