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This might be a very silly question, but I can't find the answer
I'm using Fuel injector pulsewidth calculator to check what my idle pulsewidth should be, and from what I can see the on-line calculator gives PW 2.76 and REQ_FUEL 5.59
I have currently PW 4(ish) and REQ_FUEL 10
i was able to get reasonable results with that calculator. but that's kind of surprising, because there are so many assumptions. i don't think that calculator is very useful in tuning your idle.
as a rule of thumb, idle pulsewidth should be tuned so that you have maximum vacuum at your target RPM. it can be a bit of an iterative exercise, because as you change PW, idle speed can/will change. i think a combo of watching your vacuum and listening to your motor will get you where you want to be. mine likes to idle pretty rich ~12.5 AFR, so that's what i give it. can also watch idle temps, but ignition timing has a pretty big effect on that too.
TheMonkey wrote:i was able to get reasonable results with that calculator. but that's kind of surprising, because there are so many assumptions. i don't think that calculator is very useful in tuning your idle.
I was thinking about that this morning, the calculator does not take in consideration your cam and heads etc..... too many factors involved I believe.
TheMonkey wrote:
as a rule of thumb, idle pulsewidth should be tuned so that you have maximum vacuum at your target RPM. it can be a bit of an iterative exercise, because as you change PW, idle speed can/will change. i think a combo of watching your vacuum and listening to your motor will get you where you want to be. mine likes to idle pretty rich ~12.5 AFR, so that's what i give it. can also watch idle temps, but ignition timing has a pretty big effect on that too.
Is the idle pulsewidth something you can adjust in Megatune?
65looter wrote:
.....
Is the idle pulsewidth something you can adjust in Megatune?
idle PW will change as you move your VE map up and down. more VE in the idle region will give more PW, vice versa. you can just tweak VE map to change PWs.
but, i kind of did it different. because the idle portion of VE map can get lumpy if you start moving one map point at a time, i temporarily used 'injector opening time' to move the absolute value of idle PW up and down and set idle set screw to a constant RPM. then, looked at data logs to determine what my best idle PW was. when i found what my target idle PW was, then i put 'injector opening time' where it belonged, and adjusted the entire idle region of the VE map to where it would give me my target idle PW.
don't you adjust your idle speed with a set screw? if your throttle body butterflies are all the way closed, then you must be letting too much air in through the IAC. pretty good info on tuning idle in the MM: http://www.megamanual.com/ms2/tune.htm#idle
TheMonkey wrote:my motor is a traditional Pontiac.
don't you adjust your idle speed with a set screw? if your throttle body butterflies are all the way closed, then you must be letting too much air in through the IAC. pretty good info on tuning idle in the MM: http://www.megamanual.com/ms2/tune.htm#idle
I have no IAC (yet), never had any problem idling at 800/850 with a Holley 650 double pumper.
All I've done is replaced the carb with the auto-nomics throttle body
The idle screw is nearly fully open (or closed, depending on how you see a glass half empty or half full...), the butterflies are barely opened and I get about 960 rpms, if I screw in the idle screw (no punt....) rpms will rise and I unscrew it the idle rpms will drop. But the idle screw is very sensitive, it doesn't take much to go from 1000 rpms to 600 without touching the VE.
Do you have a WBO2? If so what is the AFR at idle? If you don't have a WB you might try changing the idle VE bins for lowest kPa and than try lowering RPM via the idle screw.
How do you control timing? If it's by MS than you have another other option to improve idle RPM.
66fb wrote:Do you have a WBO2? If so what is the AFR at idle? If you don't have a WB you might try changing the idle VE bins for lowest kPa and than try lowering RPM via the idle screw.
How do you control timing? If it's by MS than you have another other option to improve idle RPM.
I have an LC-1, at idle the AFR is about 12 to 13.
Timing is controlled by dizzy and MSD-6A
