Nuisance RPM drop after throttle blip GC 5.7 Comp HRT

[StupidJeep]

Hey all. For the most part I have managed to figure out most of my problems (tuning related, personal is still up for debate). However I still have a nuisance problem that I have pretty much always had. as per usual I cam make it worse but never really better. Generally speaking it will do it mostly in drive but a bit in P/N. Foot on the break and blip the throttle it will rev like you would expect but after letting off it will dip and do a couple swings and recover. I would generally expect it to be an air flow thing or PID control issue. I've played with both but never to much success. Attached is stock tune current tune and log. And yes the VE always need s work to some extent. The last couple minutes of the log ( screen shot) shows my problem...

Input or advice always appreciated.

Screenshot 2024-11-26 183802.png
2007 Jeep Stock (1).hpt
nov 26. GC 5.7 rpm dip.hpt
Nov 26 GC rpm dip.hpl

[Spray-Cam Hell-Ram]

I cant guarantee this is gonna fix the issue you are having but you can load this up and give it a shot and see if anything improves...

[StupidJeep]

Thanks ill check it out here in a day or two. Appreciate it.

[StupidJeep]

It did seem to help quite a bit after some adjustments. The VE table was wild! Started to clean it up but then my laptop battery went for a shit. But so far its been good, I just have some lean condition off throttle surges to fix up.

Thanks for the help again

[StupidJeep]

So Im back to this big oscillation when I give it throttle and hold the brake and then let off the throttle.

Screenshot 2025 throttle blip.png

Any insight is appreciated.

MAr 29 latest.hpt
MAr 29 latest with throttle surge again.hpl

[DodgeBoy_8HP]

Did you do any change in the vehicle?

[LilSick]

So Im back to this big oscillation when I give it throttle and hold the brake and then let off the throttle.

your fuel trims are really sexy

i was like why is he posting a graph for a tip in issue?

oh

duh

ego.

i get it...


at tip in you are losing all lead

going retarded

it prolly is not as noticeable when the car can move and the tune can then catch up, but with you holding the brake this retardation is damn near causing the engine to stall

your wide band(s) are not being logged so i do not know where the FA is during the issue

[StupidJeep]

"It prolly is not as noticeable when the car can move and the tune can then catch up, but with you holding the brake this retardation is damn near causing the engine to stall

your wide band(s) are not being logged so i do not know where the FA is during the issue"

This is pretty accurate... I guess I have a couple issues I'm not sure how to deal with. I'm guessing whatever my tip in problem is and potentially a an idle PID problem?
As far as what the wide band is doing, that's a good question. Ive watched it on the brake loaded up but it stays around the 14:7 -14:8 mark right till I let off then it goes rich as the rpm drops off then big swing lean and then settles down....However the fuel trims are likely keeping it at stoich when I load it up on the brake..?

[StupidJeep]

Did you do any change in the vehicle?

Ive likely done a few minor changes over the last few months. Its always done it, its just a matter of how much it does it. Spraycam helped it quite a bit with his fix a while back and that helped on the sifting from forward to reverse and giving a bit of throttle just backing in to the driveway sorta thing. When I really load it up though it still gets angry and does the big swing.

[LaBrat]

So i had been playing with my tune, as I have the same issue but to a much lesser degree. I actually feel I have almost completely eliminated this issue now, and it looks to be due to the idle PID control.

What I had done is I zero'd out the throttle proportional control for +-100rpm, and lessened it at 200 RPM. To combat this, I increased spark proportional by 10%.

By doing this, the throttle itself felt to follow my pedal rather than be influenced by the algorithm and it took away many of the dips I had.

I also have my friction torque loss table set lower than stock in the lower pedal ranges, I felt that had an effect as well. I would attempt the idle PID items first though.

To boot, my idle quality actually improved as well in drive, less bucking. I left it nice and lopey in park, though.

[StupidJeep]

I managed to rectify my big swings more less buy dropping the Min airflow table in the first two rows quite a bit. Which seems odd as I was of the assumption that you typically add to those column when adding a bigger cam....

[LilSick]

i do not know what you are calling "a bigger cam" or where it is installed, but increasing duration and tightening the lobe centers both increase overlap

overlap kills airflow at low rpm

[StupidJeep]

Fair but if you add a bunch of lift...would that not make up for anything lost? Or I guess not till higher RPM again.

[LilSick]

add a bunch of lift where

steepen the ramp and lift increases down low

snap the intake open and snap it closed and you will make more high rpm power (if the spring and valve train can control the valve) but look at where the intake valve opens

on the exhaust stroke

so the sooner and/or the quicker you open it, the more exhaust (high pressure) goes where airflow does not want it

same as when you narrow the centers or increase duration

[StupidJeep]

Kinda makes sense( a lot of this is over my head)... also light bulb moment, that explains why it was rich on first start up with the stock VE tables. Which at the time didn't make sense because I just added a "bigger cam" for more air.

[StupidJeep]

Finally actually fixed my issue after months an months of trying everything. Turns out it must have fat fingered one of the tables in Trans tune ages ago.
The TCM throttle interpret table was all at 100%. Put it back to stock and it seems 100% better now.