I've been tuning my recently rebuilt 3.2 Porsche motor, and getting a smooth and stable idle has been a challenge. I've got pretty mild cams (993 Super Sport), but they're definitely more aggressive than stock, and I also have huge fuel injectors from Injector Dynamics (duty cycle seems to peak for me at around 40%), but they did give me all the Deadtime and Small Pulsewdith data from their bench tests so I hope I can still use these to get a smooth idle. I switched to sequential fueling yesterday to smooth the idle and ensure the pulsewidths are as long as possible at idle. The car is running strong and smooth throughout the RPM range, but I'm still fighting the idle.
If I use Closed Loop, then it won't stall but it will occasionally get stuck in oscillations despite me trying almost every setting to neutralize that. I switched to Warm Up just to see if I could get things stable that way, and it's better under all conditions except when I abruptly close the throttle. This could be during an upshift, although it will rarely stall before I'm back on the throttle, but it's most annoying during downshifts when I'm taking more time to release the clutch...it will stall unless I really wait until the RPMs are already low enough to not have them drop abruptly. I've also been trying this with and without using the Idle Advance and Idle VE settings to try to make the idle more stable even while I'm not using CL for the idle valve itself. I do have the idle bypass air screw on the TB itself out several turns so that the engine idles at around 1050 rpms (about the lowest I can get any type of smooth idle) with the idle air valve closed all the way. I thought this would ensure that there was always enough air bypassing the throttle regardless of what the idle valve was doing to prevent stalls, but so far it hasn't helped.
The attached logs and msq files are from two periods idling where I just raise the RPMs and then close the throttle, progressively hitting higher RPMs and then releasing the throttle until the motor stalls. If I rev it to 3000 RPM and then close the throttle, it will stall almost all the time. I've tried all the advice in the manuals about using higher advance (ignition is dual plug EDIS) to "catch" falling RPMs, but it doesn't seem to help much even with extreme numbers in there. I've tried this both with the Idle Advance on and in the base timing table (and both). One thing that did seem to help a little, but not really solve the problem was to drastically lower the BTDC injector timing number for the ~500 rpm range. I'm just starting to tune this table since going sequential yesterday. Moving the number in that column of the table from 320 to 200 degrees seemed to make it stall far less often, but still occasionally. The second msq and log files are the same basic test with those settings.
I'm hoping someone can look at these logs and settings and see something else I'm missing that might help....thanks in advance.
Olivier
I guess I can only include 3 files. Here are the two log files and only one of the msq files. The only difference between the before and after msq files is that I changed the 500 RPM column in the Injector Timing Table from 320 (before) to 200 (after)
log file before injector timing changes:
msq file after injector timing changes:
log file after injector timing changes:
Engine stalls when throttle closed quickly
Moderators: jsmcortina, muythaibxr
Re: Engine stalls when throttle closed quickly
there is a good explanation in the manual on how to setup idle control
http://www.msextra.com/doc/pdf/html/Meg ... .4-92.html
Also after you finish tuning closed loop control and got a stable idle try to add more Dashpot adder in the closed loop idle setting this should prevent stall when lift the throttle.
http://www.msextra.com/doc/pdf/html/Meg ... .4-92.html
Also after you finish tuning closed loop control and got a stable idle try to add more Dashpot adder in the closed loop idle setting this should prevent stall when lift the throttle.
Re: Engine stalls when throttle closed quickly
Thanks yzn. I've been through that section many times and I've dialed in the dashpot adder within the CL idle...I don't have a stalling issue using CL. I only have the issue using warmup, and I've been wishing for a dashpot adder within the warmup idle settings because I think that would solve my stalling problem.