Hesitation, bogging, and stalling

[XfireZ51]

These three are probably the more frequent issues with owners of the C4 LT-5, particularly when they modify the motor.
Typically, the first things done are porting of the intake (plenum and injector housings) along w headers and exhaust.
Hesitation occurs after decel, bogging usually from standing start. The stalling can occur when freewheeling to a stop. The more rapid the decel, the more likely the stalling. One other thing w freewheeling is an oscillation of the idle as u roll to a stop. I’ve also observed it on a slow crawl, in neutral, and putting a load on the motor such as turning the steering wheel.
I’ve done my own changes like setting Min Air properly, and modifying SA for idle too low or too high along w increasing Idle SA. Increased the MPH for Idle control. Lowered PropGain v gm/sec at 0 gms/sec. And I recently increased MAX Airflow for Idle from 16gm/sec to 20 because I noted in the logs, that at idle I was exceeding 16. Again due to increased airflow from the modifications. MAP/RPM boundries have also been bumped from stock. AE PW v MAP delta also increased.
Recently, I believe I’ve been able to really control these issues better. There are three parameters in the $D0/A Masks that pertain to TPS% for C/L Idle, TPS% for IAC CONTROL, and then the IAC TF/MIN TF v MPH tables.

Thought I would put this out there and see what the experience of the group here has been w similar issues on various motors.
comments?

[tiegsd]

No experience really, still a ZR-1 maintenance newbie, but definitely dig that kind of control system tech stuff.

[Ccmano]

Dom,
The last iteration of the tune you did for me went a long way to mitigate the coasting to tip-in hesitation/bogging and intermittent stalling. The stalling has not reoccurred and the hesitation is much less pronounced and less often. For this last iteration I know you increased the AE another 8%.

Since you have been teaching me and I have been trying to teach myself the tuning process through extensive reading on the subject, as you know I bought all the hardware to evaluate and make changes myself.

In the last few days I have made the following changes to that last tune. I smoothed both the port throttle open VE tables. (My secondaries have been eliminated so the engine runs primarily off these tables) I did that one column and row a time. I utilized the “smoothing” program in TunerPro. In that process I found that the 2000rpm row that appears on both tables significantly didn’t match. I have read that it is important they match. So I matched the row for both tables.

I drove the car yesterday and the change is remarkable, hesitation/bogging are gone and there was no stalling, not even an rpm drop. Surprisingly the engine has never run as smoothly as it did yesterday. Previously there has been a hard to describe harshness and occasional jerkiness to it. Minor but noticeable. That was gone yesterday.

That said, one 40min drive isn’t the last word how the tune performs. I plan to data log it today or tomorrow weather permitting. I’m anxious to see where this takes us...
H
:cheers:

[XfireZ51]

Dom,
The last iteration of the tune you did for me went a long way to mitigate the coasting to tip-in hesitation/bogging and intermittent stalling. The stalling has not reoccurred and the hesitation is much less pronounced and less often. For this last iteration I know you increased the AE another 8%.

Since you have been teaching me and I have been trying to teach myself the tuning process through extensive reading on the subject, as you know I bought all the hardware to evaluate and make changes myself.

In the last few days I have made the following changes to that last tune. I smoothed both the port throttle open VE tables. (My secondaries have been eliminated so the engine runs primarily off these tables) I did that one column and row a time. I utilized the “smoothing” program in TunerPro. In that process I found that the 2000rpm row that appears on both tables significantly didn’t match. I have read that it is important they match. So I matched the row for both tables.

I drove the car yesterday and the change is remarkable, hesitation/bogging are gone and there was no stalling, not even an rpm drop. Surprisingly the engine has never run as smoothly as it did yesterday. Previously there has been a hard to describe harshness and occasional jerkiness to it. Minor but noticeable. That was gone yesterday.

That said, one 40min drive isn’t the last word how the tune performs. I plan to data log it today or tomorrow weather permitting. I’m anxious to see where this takes us...
H
:cheers:

Good to hear Hans that the AE increase made a diff. Now a datalog to confirm would be helpful particularly in regards to KC and KR. Yes getting the 2000rpm transition between low and high rpm tables is a good thing to do. U may want to check SA tables for same thing.
Which way did u go on the “smoothing”? Be interesting to see if u added or reduced VE. I also had modified the proportional gain in your last bin.

[Ccmano]

Dom, the SA tables matched at 4K rpm where it appears on both tables. Hard to say if the smoothing was richer or leaner overall. Individual cell changes went in both directions. If anything I would say table #1 was overall leaner and table #2 was overall richer. The weather today did not allow for a drive. Maybe tomorrow. I’ll send you a copy of the .bin I’m running so we’re on the same page.
H
:cheers:

[ghlkal]

These three are probably the more frequent issues with owners of the C4 LT-5, particularly when they modify the motor.
Typically, the first things done are porting of the intake (plenum and injector housings) along w headers and exhaust.
Hesitation occurs after decel, bogging usually from standing start. The stalling can occur when freewheeling to a stop. The more rapid the decel, the more likely the stalling. One other thing w freewheeling is an oscillation of the idle as u roll to a stop. I’ve also observed it on a slow crawl, in neutral, and putting a load on the motor such as turning the steering wheel.



Hi Dom,


These describe my issues exactly.



My engine modifications are as you list also (ported plenum and IH, headers, exhaust)


I'd love to have the tune modified to correct this. PM on the way :)


Gary

[Ccmano]

Ever since we increased the AE and smoothed the tune my stalling and bogging on coast to throttle is completely gone. Runs smooth as a stock tune without mods. Dom did a great job. Highly recommended.
H
:cheers: