Strange Coast/Neutral AFR and STFTs

[flapjack]

Alright, so its been a while since I've posted here. Lots of life events happening but I've finally gotten back to work on the money pit.

Log is attached below.

I'm gonna keep this short and sweet. I'm having an issue, where whenever the car is revved or put into neutral after driving, the following events happen in this order:

- RPM drops smoothly towards target idle.
- Upon reaching ~1000 RPM, AFR drops to 9-10 and engine starts to run rough.
- STFTs drop to -25% and holds to alleviate the sudden rich condition.
- AFR quickly climbs to 16.5-17
- STFTs slowly react and head towards 0 to alleviate the new lean condition.
- AFR finally stabilizes at 14.55-14.7.
- Engine runs smoothly, STFT and LTFTs stay within 3%

I can get the car to do that consistently, over and over again as many times as I want. Happens every time and is very annoying.

I thought it was an exhaust leak at first, tested for that and I actually found a leak at the DP flange to the turbo. Shitty ebay flange was warped so I pulled the DP out, took an angle grinder and ground the face down as flat as I could get it. That fixed the leak but the problem still persists.

I've done hours of googling, searching this forum, and banging my head against a wall trying to figure out whats causing this to no avail. I'm going to try a boost leak test tomorrow for the hell of it but the symptoms don't seem to point to a boost leak.

I recently installed a BNR S3 with these supporting mods:

- HTP 4" Intake
- eBay Catless DP
- Mac35 3 port BCS
- Bosch 3.5 BAR MAP
- Freektune Custom Tune


All other mods are in my sig.

[nebolskeetskeet]

New to reading logs, but what I am seeing is after you blipped the throttle, your MAF voltage was erratic (went down then up, during the decrease in RPM). Your calculated load followed this trend, and you injector duty cycle went up when load increased, which made your AFRs drop.

Could it be something to do with your MAF? I am assuming it was calibrated with your 4" intake.

Like I said, I am new to this so I could be missing something.

[shamie]

I wonder if this is the "You might have idle issues if you get an intake bigger than 3"." syndrome?

[flapjack]

@nebolskeetskeet Yeah that's all correct. Justin was informed of the 4" intake before the tuning process began and this isn't his first rodeo so the MAF cal should be spot on.

Things I've done since first post:

- Intake Boost Leak Test
- Exhaust Boost Leak Test
- Wiggled MAF Sensor and Surrounding Harness

The boost leak tests showed perfect results on both intake and exhaust. Not a single damn leak, shes sealed tighter than a virgin on both ends.

Also I read in another lengthy post here that a loose/broken ground wire on the MAF sensor can cause AFR and voltage to go nuts. Considering I had just relocated the battery and ECU, I thought I'd give this a try but it changed nothing.

[5doorsoffury]

I would check the bpv. I have a 4"intake so my idle was set to 1k. When i was coasting and put it into neutral or approaching a red light and put it into neutral after accelerating the rpms would drop past idle. I would go rich and then they would bouch back. It was annoying and would cause a hesitation when lazy shifting.

It turned out to be my bpv. It was leaking during idle transitions.

I took it apart cleaned and lubed it up. Cranked the spring down to make it seal better and problem solved. Now the needle drops and lands softly at my idle rpm.

[flapjack]

Originally Posted by 5doorsoffury I would check the bpv. I have a 4"intake so my idle was set to 1k. When i was coasting and put it into neutral or approaching a red light and put it into neutral after accelerating the rpms would drop past idle. I would go rich and then they would bouch back. It was annoying and would cause a hesitation when lazy shifting. It turned out to be my bpv. It was leaking during idle transitions. I took it apart cleaned and lubed it up. Cranked the spring down to make it seal better and problem solved. Now the needle drops and lands softly at my idle rpm.

That sounds EXACTLY like the problems I'm having.

Not just my coasting/return to idle is weird, but normal shifting feels jerky and sloppy.
Not to mention when shifting, I can see AFRs going all over the place for a spit second. Its like between shifts the car freaks out.

Also cruise AFRs are 14.41-14.55 which seems weird.


Where was your bpv leaking from? I just did a boost leak test and found no leaks on it anywhere. Maybe it would only show in vacuum though?

[mituc]

3.79g/s of air for 0.97V seems about 16-20% too much. Maybe the MAF cal is a bit damaged in the low voltage range?
I tuned recently someone with a custom 4" intake, when I get home I can take a look and see what values I've put in there, otherwise that MAF cal is pretty good after only 2-3 MAF calibration logs.

[flapjack]

Originally Posted by mituc 3.79g/s of air for 0.97V seems about 16-20% too much. Maybe the MAF cal is a bit damaged in the low voltage range? I tuned recently someone with a custom 4" intake, when I get home I can take a look and see what values I've put in there, otherwise that MAF cal is pretty good after only 2-3 MAF calibration logs.

That's what I was thinking. Thanks for your help I really appreciate it.

I thought it might be Justin just isn't finished dialing in the MAF yet? But when I asked about this issue he said trims look good so its fine. I recently sent him the log in this post with a more in depth explanation of the issue, so we'll see what he says.

[mituc]

Originally Posted by flapjack That's what I was thinking. Thanks for your help I really appreciate it.

See how the attached works for you. If it's off it's going to be off by only a few percents, so nothing that will trigger the issues that you have now unless it's hardware related.

[5doorsoffury]

It was opening at idle like the spring was to soft but it wasent. It wasnt leaking to atmosphere it was opening on manafold vacume and when i hit the gas i think the valve didnt seal fast enuf. All i know is it passed the boostleak test. Try tightening the spring and clean and lube the valve. I used red synethetic mobile 1 grease. I never figured out what was going but then again i never gave it much thought after i fixed it. Maby the valve staying open caused a lot of recurced air to flood the area around the maf making the readings fucked up. I really dont know. Was relieved since it was happening for months. On the plus side i fixed every leak in the car going nuts trying to fix that issue.

[flapjack]

Alright I'll give this a try.

Sorry if this is a dumb question but am I able to use this map on an accessport? Thats what I'm currently using.

[mituc]

Originally Posted by flapjack Sorry if this is a dumb question but am I able to use this map on an accessport? Thats what I'm currently using.

If you can edit your maps then yes. Otherwise no.
However your tunes is a pretty good one, so I'll bring this issue up to your tuner and not provide him with the solution, because he will most likely have a solution for you.