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Rough acceleration from stop


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I am having issues accelerating from a stop in first gear. If I gently ease into the throttle, I can get it to pull away fairly smooth - however that's annoying and not the purpose of the car lol. If I want to accelerate more aggressively from a stop it's pretty rough - the more throttle I give it the more it will bog down.

The car is an 800HP R32 GTR running on ethanol - so idle isn't the best as is but it's fairly tame. I have it set at 1000 and CL keeps it around 980-1020. Car drives great and pulls hard otherwise. 

The car does have a BMW GS7 DCT gearbox. I am using HTG GCU and running closed loop take up and shifting strategies, I've spent countless hours playing with the strength and anti-stall tables in the GCU thinking the issue was on that side, but I am now starting to think maybe the issue is on the ECU side of things.

I tried playing with the neutral/park step, I initially set this to 2% and it just caused RPMs to continuously climb, CL idle settings seemed to just override anything less than this after a couple of seconds.

I've attached my current map and a couple log files starting in 1st gear so you can see what's happening. If anyone has any ideas or sees anything that sticks out let me know!

Note: last part of the second log I did light acceleration to show smoothness.

MAP - JAN 21.pclr first gear acceleration 2.llg first gear acceleration.llg

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Is it still ITB's or a single throttle?  Your main issue appears to be you have way too much accel fuel, you are getting about 70-80% extra fuel when you move the throttle, typically I expect to see more like only 30% extra for this sort of movement speed. 

I would start by reducing the cold correction to 1.0 in the 70 & 80°C cells, probably drop the 60°C cell a bit also.  In the first log your coolant drops to 73°C as time goes on so that alone is giving about 1.6x more accel fuel.  If it still bogs with the cold correction reduced, then I would drop the clamp in the 1500RPM cell or wherever it seems to get too much fuel.  It almost looks like the sens value is too high but it is only 15 in the map you attached, so not sure if that has different when the log was recorded and has since been changed or something?  

Your throttle control looks like it could be improved also, you get quite a lot of overshoot so this will tend to exaggerate the accel fuel also.  




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I appreciate the insights. No ITB's, I am on a single throttle (Bosch 82mm on large Plazmaman manifold). I didn't change the sens value(or anything else) between logs.

I have two large e-fans that turn on at 175F(80C) - while driving I never really hit this temp - only at idle really. But when they do kick in they basically drop the temp down 165F(73C) very quickly, so the car basically lives in the 73-80C range. I'll lower these values down to 1.0 as suggested and drop clamp from there if needed!

For throttle control, what would generally cause it to overshoot like this? Any suggestions on what to look for here?

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6 hours ago, mk3design said:

For throttle control, what would generally cause it to overshoot like this? Any suggestions on what to look for here?

Just PID tuning.  I dont remember doing one of the bosch throttles on a G4+, but looking at your values I suspect you need more P & D, less I.

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Alright, I tried lowering the suggested cold correction values to 1.0(map attached), it was better but definitely not fixed. I played with the 1000-1500 clamp values but seemed like if I went too low with it, it would be worse, and lowering it in small numbers didn't seem do too much. I also reset this to the out of the box enrichment values I've seen posted in another thread which seemed to make it worse.

Here are some logs and the last map I tried.

I may just try scheduling a road tune with my tuner, I'd just hate to spend the $$ if it's something simple.


fga4.llg first gear acceleration 3.llg first gear acceleration 4.llg MAP - JAN22 - ACCEL ENRICHMENT MODS.pclr

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