Random AFR changes, leaner WOT causing breakup
 

So I've been trying to work out this intermittent problem I have been having. Its a 2006 evo on aem v2. Flex fuel tuned.

Here is an example of whats going on and how its so intermittent. I can drive the car to work and do a WOT pull and it be smooth. Then on way home from work, my WOT pull will have misfires/breakup. Sometimes its not that bad, sometimes worse. Sometimes I can go 2-3 days with no issues, then it will come back for couple days. It comes and goes randomly. This is all on same gas, boost level, etc...no changes.

Something I have noticed in my logs is that on pulls that go smooth, my AFRs are in the mid 11s. On runs with breakup/misfires, my AFRs are around 12.0 flat; which by no means is horrible, but just something I noticed. The two screen shots i posted of my two logs will show you what I mean. These two logs are same day, same gas, only 4 hours apart.

Also, I am sometimes able to predict if the breakup/misfires will happen before doing a WOT pull by the cars drivability beforehand. Just normal driving the AFRs are different, like slightly leaner, and in between shifts there is a sputter and it goes really lean for split second. When the car drives good though, my WOT will more than likely be clean.

I have tried all the usual things, like new plugs, change gaps, new cam sensor, etc..but nothing has fixed it yet. I am wondering what is causing my AFRs to change so sporadically and my WOT pulls to be leaner than others.

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I assume you've already checked that your fuel pressure is ok. Next, you'll need to verify injector pulsewidth. When you're running lean, did it actually put out less injector pulsewidth compared to when it's running normally?

If it did, then you need to figure out which parameter is causing the issue. Log and compare engine load, intake air temp, coolant temp, flexfuel sensor, ect. Anything that affect fuel compensation.

Let us know how it goes.

Fuel pressure stays consistent in low 70s. Injectors pulse width shows no major changes between good and bad pulls.

Then it's most likely ignition misfire. Widebands tend to show apparent lean AFR on misfiring motors.

Are you certain there are no wiring issues with the +12v supply and ground for the coils?
A quick and dirty way would be to run parallel wires from the battery and splice them near the connector.

I guess a wiring issue could have started randomly. Its a sparktech non cdi sequential system. Followed their install instructions. I did not have any issues for a few months after the build and tune. It just started randomly one day.

Can you post the actual logs on here?.... tough to see thru screen shots whats going with everything else.

I don't know how to post the log on here. I can email it to you.

update...I have noticed a trend. First drive of the day is smooth. Driveability is good and WOT pulls are smooth. As the day goes on and I drive the car a couple more times, I notice the AFRs get leaner at idle, cruising, wot, everything. Car will sit for a couple of days before I drive it again and this cycle repeats. And I know its not temperature related because temps are not changing by more than 2-3 degrees.

Do you happen to disconnect the battery while the car sits before you drive the next cycle?

no, it stays connected

Did you ever fix the issue?