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[Cornfed54]

I've seen multiple people say it's not JB4, but seems most prevalent on JB4 cars to me. Only time I've ever experienced it was when JB4 was in for a couple of months in 2016. Had to mess with 10, 11, 12, FF, PID, etc. and torque request to get rid of it. I've never had surging flash only before or since.

To discount JB4 as a source, it needs to be completely removed from the car. Any time it's connected, it controls boost.

That’s a good data point, I’m JB4 and I haven’t tried completely removing it to see if that’s the issue. Your point makes sense though, the JB4 is trying to make the car control boost differently than it would on its own. The menu settings you referred to, all probably affect the issue in one way or another to exacerbate the problem.

 

[RSL]

I pulled it completely. Surge still there.

Flash back to a primary bin and reset adaptations or leave the OTS BEF in after you pulled it? Yours may be another issue.

That’s a good data point, I’m JB4 and I haven’t tried completely removing it to see if that’s the issue. Your point makes sense though, the JB4 is trying to make the car control boost differently than it would on its own. The menu settings you referred to, all probably affect the issue in one way or another to exacerbate the problem.

Exactly. That thing was in boost no matter how lightly and consistently I was on the pedal. It would cycle between few in/Hg and 3-4psi with 0psi target. Would run over and the back off and then boost again needlessly, run over and then back off and that was the cycle. If I changed pedal position slightly (target), it would stop. When boost moves, everything follows with it: load, AFR, trims, etc., so it can be hard to determine what's the chicken and what's the egg.

JB4 + 3.5 bar or 4 bar may also help facilitate it.

 

[NoQuarter]

I went to mhd flash after.

I will reset adaptations again. Even thou its not present when I start driving. Comes on after car warms up.

Similar to my experience as well couple summers ago in the Z4. 3,000 mile road trip

Start off the day with a cold start, drive some hours, no problems. Make a pit stop, get back in the car, hit the highway, start getting the subtle surging, change speed just a bit and it goes away.

Haven't noticed it for a long time but I didn't actually do anything to fix it. It could still be there for all I know, I haven't had the Z on a long continuous cruise that didn't require frequent speed changes very often.

No JB4 installed. MHD tunes only

 

[all4bspinnin]

Step 1. Remove JB4
Step 2. If your o2 sensors are old, replace them.
Step 3. Reset adaptations (except throttle)
Step 4. Get a tune with a properly setup scalar table

I was just explaining this the other day. The oscillation is from your AFR going rich/lean/rich/lean as a result of your stft over/under correcting.

 

[RSL]

I went to mhd flash after.

I will reset adaptations again. Even thou its not present when I start driving. Comes on after car warms up.

If it does it flash only, I'd probably lean toward a sensor or the flash. If it were me, I'd flash back to stock or at least Stage 0 rather than a modified bin and check.

A lot changes between cold and operating temp modes, but ambient temps may play into it (WGDC, MAF calcs, etc.). If it doesn't do it when the car is cold, seems like something that could be tuned away to me.

 

[Jeffman]

I was just explaining this the other day. The oscillation is from your AFR going rich/lean/rich/lean as a result of your stft over/under correcting.

I believe this is what the DME does intentionally during a drive cycle for checking O2 Sensors functioning. My guess is some of our tuned cars tend to be very sensitive to changes in AFR which results in surging.

 

[RSL]

Hmm, did you log on that by any chance? IIRC, bank 2 O2 looked a bit odd to me in your JB4 log compared to bank 1. Might be able to get them out of the top, but I just pull the heat shield over the tie rod boot and bolt on the passenger side steering rack, loosen the other bolt on the steering rack and plenty of room to get them from below.

As for the other thoughts, load moves AFR targets, not the other way around. If AFRs and trims are surging while load is constant, might be a cause, but if load/boost are moving up/down, they are causing the movement in those parameters, not responding to them.

When injector adaptations occur during driving, the WGs are wide open. It would be very easy to see where the WGs are during the surging if it's logged.

 

[RSL]

Harder to duplicate this morning, but got 2 logs where bank 2 lambda is jumpy.

https://datazap.me/u/fredcase/log-1528300557?log=0&data=16-17-22

https://datazap.me/u/fredcase/log-1528300711?log=0&data=16-17-22

https://datazap.me/u/fredcase/log-1528300557?log=2&data=3-4-18-19-22

Load is jumpy. Hard to tell on my phone, but looks primarily caused by calculated boost. If it's calculated boost and does it on JB4 also, I'd probably lean towards VANOS, but MAF isn't jumpy, so maybe not. That's some super low ambient pressure too, which may be impacting calcs and PID though. If you have a map pack, might want to try an OTS map just to try the different PID and see if it smooths out by any chance. Might also reset VANOS adaptations and clean the solenoids if they're due.

Short of that, I'd log VANOS request and actual, P and D error, WGDC base and WGDC after PID, MAF request and actual when this occurs and let's see what they look like. If we can't locate the cause, might be able to smooth out the response at least.

 

[chrisdfv]

How did you do that?

Like a dummy I forgot to check the "invert bank 1" toggle when doing my ST tune. So 0 wgdc was actually all of it lol

To discount JB4 as a source, it needs to be completely removed from the car. Any time it's connected, it controls boost.

I was flash only for weeks on a flash only tune, and the problem was still there. Not to mention that I'm single turbo so under low load and low rpm scenarios like highway cruising I don't have any wgdc active since it's below my wastegate spring.

Step 1. Remove JB4
Step 2. If your o2 sensors are old, replace them.
Step 3. Reset adaptations (except throttle)
Step 4. Get a tune with a properly setup scalar table

I was just explaining this the other day. The oscillation is from your AFR going rich/lean/rich/lean as a result of your stft over/under correcting.

I had this problem present with all 4 brand new o2 sensors, and my scalar was good. It only went away after replacing the throttle body in my case. No tune changes. I've been surge free for months now.

 

[chrisdfv]

Did you have jumpy afr?

yes. Just like every body else has mentioned, and every log I've seen. my afr and trims would bounce up and down.

https://datazap.me/u/cd919/throttle-issue?log=0&data=1-4-14-18-24

 

[RSL]

I'm sure there are a lot of things that will cause surging, the hard part is figuring out which it is. It's super annoying in the meantime though.

 

[Cornfed54]

Harder to duplicate this morning, but got 2 logs where bank 2 lambda is jumpy.

https://datazap.me/u/fredcase/log-1528300557?log=0&data=16-17-22

https://datazap.me/u/fredcase/log-1528300711?log=0&data=16-17-22

Are these logs after resetting adaptations and did you end up getting new O2 sensors? Both banks on mine act this way. I just adjusted my tune’s fuel scaler tables to see if that effects it for better or worse. I’ll let you know how that goes....

 

[RSL]

JB4 doesn't have those parameters, but did notice your JB4 logs show 0% pedal while you're moving. We're you coasting? At least one of the MHD logs shows the same behavior, but another shows the surge with pedal >0%. Starting to wonder if it's the pedal module or mapping. Was the JB4 completely out for the MHD logs? What flash is in the DME for these logs and is it set to 4/2 or 4/3?

If it surges on the stock bin, I'd personally leave the JB4 out until it's resolved. It just adds another layer of potentials to weed though.

 

[Cornfed54]

yes. Just like every body else has mentioned, and every log I've seen. my afr and trims would bounce up and down.

So you had the same issues and similar looking logs as we do, and replacing the throttle body totally resolved your symptoms? I might have to give that a shot, I wonder how it causes the trim issues and all that. I guess if throttle isn’t actually in the position that the sensor thinks it is, I could see it causing some big issues like these on the fueling side. Perhaps that’s why it only happens at very light load, pedal input, it’s riding right on the verge of being 0. Did your throttle % values seem normal in your logs when you had the issue? As in, did you see any significant fluctuation in the throttle position readings while your trims were bouncing all over?

 

[Cornfed54]

This morning, I changed my fuel scaler table, before the changes, I had it setup at 1.4’s tapering in the “port injection zone” to about 1.14. I changed the 1.4’s to 1.34 and left the high load/ port injection territory alone for the most part. It did seem to help the severity of my surging at low throttle some but it’s still present. My trims look good otherwise except very very light load, I can’t see them being the culprit, I’m no pro tuner though so any advice is greatly appreciated!

 

[RSL]

All MHD logs were taken with JB4 physically removed. Throttle may show 0 because I may have been using cruise control.

JB4 logs were pump bef

MHD logs are map 0 atm, first ones may have been stage 2+

oops, messed up, wrong log above, here is one with requested parameters

https://datazap.me/u/fredcase/log-1528386794?log=0&data=15

Cruise would cause 0% pedal. All the actuals are jumpy, so load or a calc going into load looks like the culprit. PID is a little active and could be toned down, but not sure it's the root cause. Either way, don't want it pushing much or at all when target is 0. No difference between the stage 0 and 2 maps for the surge?

https://datazap.me/u/fredcase/log-1528386794?log=0&data=8-9-12-15-23-25&solo=3-4-18

Always handy having 2 N54s for spare parts lol

 

[08_335i]

I've had this problem for years and years... Had it back when twins, still have it ST. I've replaced everything with the exception of the throttle body. Starting to question if it's worth the chance to replace it. Most of my driving is where this stupid surging shit occurs.

 

[RSL]

are tmap and map sensors the same part number?

Nope, they have different pressure resolutions. They might physically be interchangeable, but will give very different results.

 

[RSL]

Ouch. No indication of where it's going?

 

[ShocknAwe]

Pull your belly pan and look at the bottom of the engine just behind the sway bar. Oil pan is there. Huge leaks possible there. Now, not sure why that would cause surging though.

Also, not sure if you've tried this or discussed this ad-nauseum already, but have you looked at bank2 02 sensors? Maybe they're getting ruined by oil leak in bank2 turbo?