2007 WRX STi fluctuating AFR, misfires at idle, ignition noise on ECU, no CEL

Hi All,
My ultimate struggle is a very unstable/fluctuating AFR at steady state operation.
The engine of my car is recently rebuilt and I am trying to do a base tune for it, but I am not able to do a MAF scaling due to the inconsistent readings.
I spent lot of time researching of potential causes and was checking lots of things, including cam/crank relation and while I was recently playing with my pico I realized that the MAF sensor ground has a ~400mV amplitude signal clearly rooted from the ground side of the ignition coils (COP).

Do you guys know if this is normal?
It seems to me that the ECU is not filtering out the residual signal going from the coils on the ground wire and it transfers that to other ground pins.
If this is not normal, then should this be a faulty ECU or something else?

I am attaching couple of pico files.

Thanks a lot for your help.
Béla

not a real technician yet but I did sleep in a holiday inn last night !!! I would imagine a good maf signal is important even more so with a turbo engine are there any other systems and can you geta decent maf reading at wot the maf must be big enough for turbo applications i.e. 3-4 bar a misfire count might be done I am wondering which cylinders are misfiring and on what side of the boxer I think they use wastespark ignition as far as those afr sensors I am in the dark I am still trying to master o2 senarios and troubleshooting procedures those afr confuse me

rozsko wrote: the MAF sensor ground has a ~400mV amplitude signal clearly rooted from the ground side of the ignition coils (COP).

Do you guys know if this is normal?
It seems to me that the ECU is not filtering out the residual signal going from the coils on the ground wire and it transfers that to other ground pins.

I have a feeling it may not be the problem.
Make sure your scope leads aren't going close to something else that could cause the interference - sometimes they pick up an induced voltage.
Someone who knows more may prove me wrong but I have also got myself barking up the wrong tree many times while looking at interference on scope patterns.
Perhaps also check the ecu earths in case there is a problem there - maybe they go somewhere on the engine and aren't properly tightened.

The only cyl that I never saw misfiring is #1, but the worst is #2, #4 following.
The maf reading is similarly unstable throutout the whole mafV range, including both idle and wot.

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I checked the ECU grounds and noise is exactly same as on the maf ground, so I am pretty sure this is not something the the scope leads pick up.
What is strange though is that if I check the ground points on top of the intake manifold, there is no noise. If I go to the following point that I can backprobe in the harness (end connector of the engine harness) , the noise is there.

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Scaling the maf for an intake? Stock injectors? Has the car ever run properly since rebuild? Have you verified cam timing?

fudgie wrote: Scaling the maf for an intake? Stock injectors? Has the car ever run properly since rebuild? Have you verified cam timing?

Correct. Scaling the MAF for a 72mm diameter intake. (stock is 63mm if I remember correctly)
Injectors are DW850s, so no, they are not stock, but they were scaled with the stock intake and maf housing.
Unfortunately no. I am struggling with this for more then a year now with on and off the car as I have family and job to take care of.
Cam timing is retarded a bit compared to stock if that is what you mean and I also checked the cam-crank correlation and it is spot on. Checked the belt as well and the cam/crank sprockets are aligned perfectly.

When was the aftermarket air mass meter installed? Are you able to see target and actual cam positions? Cobb AP?

fudgie wrote: When was the aftermarket air mass meter installed? Are you able to see target and actual cam positions? Cobb AP?

I didn't want to be too lengthy on the story, but here you go.
Bought the car in 2015. Used it for 500miles and it consumed 1 gallon of coolant. Long story short, ended up putting a brand new IAG block and Cosworth heads in it.
I bought the car with an hks filter fitted already. Then after the rebuild I fitted a 70mm APS CAI and tried to scale that. I was then advised against the APS unit as it is quite curvie (if that is a word ) and might introduce turbulence in the air stream. So then (1 week ago) I got this custom unit made (with little hope though) and tried to scale the maf again. It is probably a little better, but far from consistent, even with constant load.
So I am back where I was couple of months ago with the maf ground having 300mV potential to the battery ground.

On the cam, yes I can see those. Both commanded and actual cam angle are 0.
I am using EcuEdit and RomRaider. The AP is not compatible with my EDM ecu.

Oh, one more thing. The maf sensor itself is not aftermarket. It is genuine Denso.

Have u retained all the original ground points? Engine, body, chassis, trans? Also have u altered the physical ground cables, or replaced them with aftermarket, possibly lower quality cables?

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