135i Power surge after throttle closures

[jp1]

Hi chaps,

I started a thread a couple of weeks back with details of boost overshoots I am experiencing with my Cobb OTS maps, pretty sure after some good advice from you all that can be sorted with a pro tune so that's all good.

I've since been concentrating on another issue that I'm at a bit of a loss as to what is causing it. Before I go ahead with a pro tune I want to rule out any issues aside the cobb mapping to save wasting time and money.

The symptoms of the problem are pronounced surges when I'm coming off the throttle, really quite disconcerting.

UK 135i I8A0S 6MT
Cobb Stage 2+ aggressive (happens on all maps, more so with higher power maps)

Log here which will hopefully show the spike after I've come off the throttle, there is clearly a second spike of req load, happens pretty much consistently.

http://datazap.me/u/jp1/log-14567308...=0&data=1-2-12

Any ideas?

Many thanks

John.

[TwistedTuning]

are you 100% sure you aren't inadvertently tapping the throttle a bit? not saying you are, just asking

[jp1]

I don't think so, I'll make a concious effort to step well off to be sure!

[jp1]

Stepped well off the peddle for this quick log as can been seen by accel ped % vs tps act %

For whatever reason its giving an additional blip when I'm closing the throttle, confused :/

http://datazap.me/u/jp1/surging?log=...-13&zoom=45-88

[bradsm87]

I forgot the name and acronym for it, but our cars have a "reverse traction control" of sorts, which is supposed to stop the wheels locking up on hard back offs. I've never seen it in a log myself though. This does look like what this functionality would do though.

[jp1]

Hmm, I've experienced it in bone dry conditions in 6th, really shouldnt be a traction issue. It feels more pronounced than the log might show too.

[mmmcookies335]

I am having the Exact same issues as you are. I am running a custom stand alone flash, FBO with inlets, Rb's and 100% E85. What are your mods?

[jyamona]

Can you add RPM to a log? It almost looks like an anti-bog measure. Also post a screenshot of your throttle angle aggression in overload table.

[jp1]

Stock turbos
Catless downpipes
Forge intercooler
Forge dv's,
Bms dci
Stock inlets
Stock exhaust.

Not aiming for too much at the moment, 400 ish hp would be nice to see but first need to get the thing running smooth, predictable power.

The anti bog thing sounds interesting but the problem doesn't seem to be rpm dependant. Will need to figure out exactly which channels to log but will add rpm. Not sure what you mean by the throttle angle aggression in overload table.

Thanks for your help chaps.

[SCGT]

I believe it's related to the loosened throttle safeties.

[jp1]

Please excuse my ignorance but what specifically are you referring to when you say "loosened throttle safeties"?

I'm only just starting to look at the array of tables that can be tweaked in access tuner, quite a learning curve!

[jp1]

Just found the throttle angle aggression table, its just the Stage 2+ aggressive map as per cobb OTS.

[shushikiary]

20 bucks your boost control PID P gain or I gain is too high.

When the cobb OTS maps first came out they had a lot of issues with overshoots and this, their newer OTS maps reduced the P gains a little, and D by a fair amount (the multiplier table, not the actual D gain table).

My car doesnt have overshoots, but does indeed pull sometimes for a fraction of a second after you let off the throttle, but that's because I have very tightly tuned PID values. My P is slighty the problem, but the I more so, as I added in a lot of integral gain. I did this because at altitude it was what it took to get the DME to fallow my boost curve the best it could. I even had a tech over at turbosmart comment at how well my boost fallows requested boost once when sending him some logs to look at when having issues with the turbosmart diverter valves.

Anyways, point is, I bet your PID is tuned just a little bit too much past damped to critically damped... if it was underdamped you'd see oscillations in boost..... basically the car keeps trying to push sense either the proportional is trying to keep you meeting boost target right when you let off, or you've built up enough integral that it keeps the car pushing until your boost error is small or negative for long enough to over power the built up integral. It could also be too high derivative gain, but that rarely causes surging like that, usually oscillations.

[jp1]

Thanks for the input shushikiary. I'll have to man up and actually start changing some values in ATR, as much as to learn enough to have some meaningful input come protune time, its just knowing where to start as a complete noob to all of this!.

I at least have some confidence that it is the cobb mapping and not an additional mechanical issue.

Many thanks to all that have helped. Please feel free to add any additional thoughts, all helps reduce this learning curve I face.

Cheers.