I think I know why my car doesn't like any midrange timing -- my somewhat restrictive muffler. I'm currently running a 3" O2 (WORKS), with the WORKS 3" DP, test pipe, WORKS 3" IP, mated up to a StealthWORKS muffler, which is a modified stock muffler. The flange on the stock muffler only has a 2.5" or so opening, so there's a significant flow disruption occurring. During WOT runs, the restriction is there....but when I let off of the throttle, that backpressure sends a shockwave all the way to the engine. By running very little mid-load timing, I'm able to avoid knock. I'll attach of log of what happens when I run a reasonable mid-load timing map.

What do you think of this theory? It makes sense to me, and I know the car didn't do this when I was running my 3" TBE.

 

I've seen the same thing tuning 100% stock evo 9's. I believe your theory is correct.

but man you are running some low timing! Although 27psi peak

 

Finding the cause of this will be a game of forensics.

 

I also have this happening.
also mid throttle, get into boost and then let off.

 

My problem was instantly cured with a 3" muffler. It was the stock muffler inlet flange and modified stock muffler (StealthWORKS) that was causing the problem. I'm back to running healthy midrange timing again.

 

That's interesting to know. All the more reason to get a good high flow exhaust.

 

John you have a stock job? I guess you don't really need to change much if you have a FQXXX.

I don't remember my car ever doing this. I have a turbo-back and a Tomei BOV so I'm on a different boat I guess.

But I'll try to keep an eye out.

 

Stock BOV. "job"?

 

sorry. I meant "your whole car is stock?"
I assumed yours was modified a lot since you're one of the ECU experts.

 

3" exhaust, Walbro, airbox mod, AVC-R, modified OEM fuel pressure regulator, sometimes meth in tank.
Hard intercooler/turbo inlet pipes as FQ spec.

 

Stock blow off "job"? Evo's don't come with blow off valves (or pressure relief) they use diverter (or bypass) valves. So if a BOV is used then it isn't stock, right?

 

We (UK) would refer to the standard unit as a recirculating dump valve or a recirculating blow off valve (as opposed to vent to atmosphere). Whatever your preferred terminology, I have the standard arrangement which we're all familiar with

 

It is funny I found this thread because I have been having a similar problem recently, but in the opposite effect. When cruising, lean into the throttle alittle and back out half way and it goes real rich (10:1) then jumps alittle lean (15.8:1) and then it settles back to 14.7:1, no knock. Mostly only happens in higher gears too. But I can make it happen on command. I have PTE 780cc injectors and so far I have tried: rescaling injectors, raising/lowering latencies, went back to stockairbox with nothing helping. Also sometimes the car freaks out and goes real lean when coming to a rolling stop with the clutch in but eventually settles back to stoich. Please keep the thread updated if you guys come across any more info .