NefMoto

I've had this issue on two MKIV's with the same file.  I've also used this identical file on other MKIV's with no such issues.  When letting off the throttle at partial load, 10-12psi boost, the car gives one good buck as the throttle plate closes and the DV is open. 

The last car that had this issue ran a commercial tune.  After I noticed the issue with my tune on this car, switched back to commercial tune and the issue is not present, transition is smooth as it should be... so it's somehow related to my tune.

Without logs, anybody care to take a stab at what this might be?  Why would the issue be so apparent on two cars but not a few others?  I do have logs of this, but there's nothing that I can really pick out.  I will try to get better logs of the situation next time I get a chance.

Overrun fuel cut?  Mine was weird when I was playing with it to get it to pop.  Can't remember what map, but I remember it having a massive effect.

I don't touch anything like that in my tune, but I will look into this as a possibility.  thank you!

I'm going to port the tune to another base file to see if it resolves the issue.

compare/play with TEMIN/TEMINVA

seems odd that you'd have to touch that for stock injectors.  will keep that in mind though.

In transferring to a 5120 hack file, I seemed to have reproduced these exact symptoms with my car.

I was running a 5120 hack file with stock MAP sensor and DSL (DSLGRAD and DSLOFS) values at stock values (halved for 5120) and all was well.  I then replaced my stock MAP sensor with a 3 bar sensor and updated the DSL values with 3 bar values.  Right away on my first drive I noticed bucking when I let off the throttle in part boost.   Even coming into throttle is less smooth than it was before.  So, it's likely related to either the MAP sensor or the scaling values in the tune, cause that's all that changed.  Will investigate more and hopefully I can get a better understanding of what's going on here.

In the instance of my car, I found the issue.  I have to log this file with my cluster fuse pulled, otherwise logs just timeout. When the fuse is pulled I get this rough in and out of throttle bucking.  Fuse in, all is well.  This does not explain the other two cars that I had a similar issue with, but at least solves my current dilemma.

Anyone care to take a stab at why the cluster fuse being pulled would cause such issues?

Can you do the same thing but just disconnect the k-line to the cluster? then you can log both conditions and compare..

good idea nyet.  I will try that if I can figure out how to pull the kline to the cluster.

One thing that I noticed in the logs with the cluster fuse pulled is that vehicle speed is always 0.  As a result, gear is also 0.  Perhaps that could cause it?

And actually, the cluster fuse pulled probably explains at least one other vehicle that I had this issue on.  Pretty sure I had to pull the fuse to log it, and I doubt that I ever ran that car with the fuse in.

I'm just chiming in while I'm in work - but that map for overrun I was talking about has an axis of gear, not sure if that's any use.

I'd tell you the map but I've not got OLS here, obv.

KFNWEGM