Going lean under boost
 

Since the hot weather came rolling it I started to get into an issue with running lean under boost. It doesn't happen all the time but after I run the car hard and it gets to running pretty hot I start to go lean. I thought this was spark blow-out since I was still on stock coil packs but, after my LS coil install today the problem still persists. I have a new fuel pump coming in tomorrow (DW200) since my Walbro 255 is starting to whine pretty loud and then I'm going to stop throwing parts at it.

My IAT is located in the intercooler endtank and I spray the intercooler down with water between all my runs.
I am running an EBC but when I run wastegate I don't get the lean condition (~6psi spring).

Attachment 231015

Here is a log

http://previewcf.turbosquid.com/Prev...46Original.jpg

Look at your MAT Air Density Table (curve). If it is pulling fuel (less than 100%) at AIT over where you tuned, then it is telling the MS to pull fuel. If that is the case, raise the right side of the curve:

https://cimg0.ibsrv.net/gimg/www.mia...940d4eca66.jpg

As in where mine is at 99, yours may be lower.

Your AFR line is whacky. Why does it look like the mountainsof New Mexico? Check your ergo settings..might be giving way too much authority.

Yes, mine were much lower. I will give this one a shot. I guess my IAT sensor is heat soaking. It sure doesn't feel very hot though.


I have it set to 15% authority. Is that considered too invasive? I have it set above 1300rpm, active above 70% TPS and delayed 2 mins after start.

Heat soaking or real values of temp either one will pull fuel if the curve says to.

Set your air temp correction to 100, all around. Screwing with those tables will make your life suck.

I think it was Braineack who explained that the gas law, doesn't know a damn thing about a turbo engine. Set those corrections to 100.

Will do. I'll test the car out tomorrow afternoon.

wait, so why have an IAT at all?

Zeroing it out (all to 100%) is for initial tuning. AIT is one of the last things to work with.

Theory says that Speed Density tuning follows the ideal gas law for temperature. Practice has found that The temp part is far from the IGL prediction.

Possible reasons:
1) Air is not an ideal gas
2) Temp should be measured in the cylinder, or at least the manifold, but that is impractical or (in the case of intake mani) is plagued with heat soak of sensor.
3) Therefore we put sensor in front of the throttle, which then does not account for throttling cooling when not wide open
4) The VE table includes some of the above corrections already (inherently) as a result of how we tune (we cannot actually sort the variables).

But we still need AIT to fine tune the curve for temp correction, and to be able to adjust idle initial target settings (if desired), and high temp Ign Advance retard.

I don't have Logviewer on this computer, so can't check. Laptop is at work. However I do not think the 3% difference in correction would make the AFR be in the 14's under boost. I would shut it down as soon as I see 14's @ 168kpa. I would say it is something to do with the fuel system. You are not seeing issues at 6PSI because most likely you are not hitting a wall with the fuel system. What are the AFR at 6PSI and the same RPM? And what injectors are you running? The duty cycles are around 50%, but then if the injector numbers are not set right, it could be not showing right!

So my first thoughts were my fuel system as well. 460cc RX7 injectors, 225 Walbro, stock FPR, new fuel filter. I have a DW200 arriving today. The AFRs around 6psi are in the 11's. I am pretty sure my req_fuel is set correctly so the duty cycle you see should be correct. I feel bad for the motor since it has seen WOT at lean AFRs a few times over the past few months. It breaks up pretty bad once it really starts to lean out. I would be more upset if this wasn't a 1.6L that I got for 200 bucks.

Just looking at that screenshot, your Fuel: Air correction is 94.3%. So 5.7% fuel being taken out - probably from MAT correction as others have noted. Double check that table.

You're also at 106% Fuel: Warmup Correction which means you might be fighting your WUE table as well. Is that set to 100 in your last cell of the table? Otherwise you'll always be in "warmup".

From the manual:

So the issue seems to still be present but much less pronounced now that I have a new fuel pump installed. I went from a Walbro 255 to a DW200 which has now changed my fuel across the whole board. Where I was once in the mid 11s @180KPA and 6000RPM, I am now in the mid 10s. So my VE table will now need to be corrected. I still have my old settings for MAT correction which I can see is still pulling fuel once hot but, not near as bad.

As for the WUE table, the settings I used were from another user here on MT. The final cell is 175* @ 106% WUE.

What Onyxyth said.

Start by correcting the WUE to be 100% by 175* or so. When you do your tuning, you want corrections to be as neutral as possible, tune VE at as constant environment as possible, then add corrections appropriately. Temps, altitude, etc.

Warm Up is for when CLT is below normal operating temperature.

Commented on wrong post. sorry

Hi,
I have similar issue. Did you get it sorted in the end?

Go back to your thread and read, their issue will not fix how messed up your tune is: https://www.miataturbo.net/megasquir...-8-vvt-105611/