Tuning Idle with Chrome - Some confusion

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Originally Posted by DrGonzo

So many different solutions to solve the same issue... But which is the better solution?? So far to fix trims I can either adjust injector scaling, start adjusting the injector latencies, or mess with the VE Table. So which one is the better solutions and how is it better over the others? Each solution may fix the trims, but what affects can each have on something else?

Adjusting Injector scaling will increase/decrease the fuel calculation and I assume also adjust the fuel table.

VE table adjustment is adjusting the airflow calculation

Adjusting Latency will keep the injectors open/closed longer

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It doesn't really matter, but to me you should solve what is incorrect. If you had stock injectors installed and the trims were off you would adjust the ve table. If you then switch to aftermarket injectors and its off adjust the injector scaling and latencies.

The point of that is if you change injectors in the future you haven't baked in changes to your airflow calculations that will need re-done.

At the end of the day it all ends up causing the ECU to command a certain injector pulsewidth at a given time, it doesn't really matter. Pick what makes the most sense to you.

FYI, there are empirical ways of experimentally confirming injector latencies, but I don't think you can effectively do that without live tuning.

I don't quite understand how injector latency or VE table changes will correct a 45% difference in trims front/rear. I do 100% agree that the correct injector scaling and latency settings should be used, it's silly not to and can be at best a PITA to tune around and at worst engine damage can result.

I have usually observed 5-6 points difference front and rear, but not more than that. I just thought its a good starting point to start out with the right stuff and see if either the front and rear gets closer or farther apart.

I'll get the latencies and post the tune when I get home here in a few hours.

IMO, you have to select the best-fit injector scaling first. Just use the injector latencies from Merlin's EVO tuning guide for your injectors for now. Once you determine what the best scaling is, then you can continue on to latencies and/or MAF table tuning.

Is your fuel pressure correct? Seems odd that you would be so rich with the settings you have.

Fuel pressure is set perfect at 43psi. Not a fuel pressure issue.

Attached is the tune I am using an and image of the latency table.

Attachment 8694
Attachment 8693

That's a lot different than what I ran on evo 560s:

http://www.chrisbehnken.com/Images/p...17631330071938

page 67:

http://www.evoscan.com/ecuflash/Merl...UIDE-V1.7a.pdf

evo 9 values

OK, So I got a little time to play with it tonight in the garage. I plugged in the numbers that Forest posted, fired it up and let it idle for about 25 min or so. The front and rear trims are a lot closer than they were before. Numbers from Evoscan where front Low fuel trim about 10.2 and rear about 4.5. So no longer in the negative and much close in range. But it is running leaner now. So I go in and drop the injectors down from 560 to about 540 and let it run at idle for about 20 min. Front trim is not maxed at 12.5 and the rear is creeping into the 8's.... How the hell is that possible. I reduced the injector scaling which should richen it up and the car gets leaner in the trims. Someone needs to explain this to me as that makes no sense at all.

Also note that those are long term trims after about 20 min or so. So plenty of time to run through a cycle. Looking at the actual trim feedbacks both banks are running between 0-3.2, and where the entire time the long term trims started going higher. So why are the long term trims so high but the feed back is showing it cycling within the 5% range it should be?

Quote:

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Originally Posted by DrGonzo

OK, So I got a little time to play with it tonight in the garage. I plugged in the numbers that Forest posted, fired it up and let it idle for about 25 min or so. The front and rear trims are a lot closer than they were before. Numbers from Evoscan where front Low fuel trim about 10.2 and rear about 4.5. So no longer in the negative and much close in range. But it is running leaner now. So I go in and drop the injectors down from 560 to about 540 and let it run at idle for about 20 min. Front trim is not maxed at 12.5 and the rear is creeping into the 8's.... How the hell is that possible. I reduced the injector scaling which should richen it up and the car gets leaner in the trims. Someone needs to explain this to me as that makes no sense at all.

Also note that those are long term trims after about 20 min or so. So plenty of time to run through a cycle. Looking at the actual trim feedbacks both banks are running between 0-3.2, and where the entire time the long term trims started going higher. So why are the long term trims so high but the feed back is showing it cycling within the 5% range it should be?

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Well, keep in mind you only changed the scaling 3%. Latencies have a high impact on idle trims because you are only in the 2ms of injector pulsewidth range or so, depending on your injector size, idle speed, afr, etc. So, a .1 change in latencies could be 5%.

The trims are additive. If long term trims are 10% and short term are 2% it will creep up to 12%. You probably just hadn't hit the ceiling before. I would select the entire latency column and right click, then multiply by 1.1 (adding 10%) and I bet that gets you pretty close.

After that I'd drive it a day or so before making big changes.