TB Air Flow Strangeness

TT331FB · 09-26-2005, 08:16 AM

A9S, 3" Pro Mass Air 42#, blow through.

My tune is pretty good except the motor dies occasionaly comming down to idle. I decided to check TB air flow. I had .46 VDC average MAFV at 600 RPM, ICS disconnected and spout out. I data logged normal idle and got 797 RPM, .45 MAFV average. Huh? Data log shows the idle spark is all over the place. The only thing I can figure is that spark is causing fluctuating MAFV giving an average lower than TB airflow. My plan is to data log idle again but with the spout out to remove the EEC efforts to control idle.

Any input?

Eric

93Cobra#2771 · 09-26-2005, 08:33 AM

Your idle spark jumping all over shows your idle is not stable - the EEC uses spark and ISC to control idle, with the quicker reacting spark getting the nodd on a surging idle.

More timing equals faster idle, less timing equals slower idle.

When coming down to an idle, is this when driving, or when sitting still? Dashpot decay may be something you need to look at...

TT331FB · 09-26-2005, 10:06 AM

Just for grins, I gonna log idle with ISC connected, spout out. I think the spark is adding instability into the loop.

93Cobra#2771 · 09-26-2005, 10:50 AM

It can do that - even spark takes SOME time to change, and it could end up chasing itself to a nice surging, dying tune...

86GT · 09-26-2005, 10:56 AM

That does seem kind of weird that the normal idle MAF is less than the base idle with ISC disconnected and spout out.

From what I have experienced, The ISC will compensate for idle if it is within some calibratable tollerance. I wish I knew the limits. If the desired RPM minus the actual RPM is out side of these limits then spark is used to bring it back into tollerance. I believe the upper limit is set by the scalar ISCLPD.

Look at function FN810. It tell the EEC what DC to send to the ISC for a given RPM error. Since your idle has been changed to 800 or so then the FN810 will need to be shifted to the right by the same amount you increase the idle. If you left it stock then the ISC never has a chance to correct until it is to late and then spark control takes over.

800- 672 = 128
Try bumping the entire curve up by 128 RPM.

I also played around with the gain control on the ISC FN860. I believe this is the same as the 'P' in a PID loop.

TT331FB · 09-26-2005, 02:24 PM

Quote:

Originally Posted by 86GT

That does seem kind of weird that the normal idle MAF is less than the base idle with ISC disconnected and spout out.

From what I have experienced, The ISC will compensate for idle if it is within some calibratable tollerance. I wish I knew the limits. If the desired RPM minus the actual RPM is out side of these limits then spark is used to bring it back into tollerance. I believe the upper limit is set by the scalar ISCLPD.

Look at function FN810. It tell the EEC what DC to send to the ISC for a given RPM error. Since your idle has been changed to 800 or so then the FN810 will need to be shifted to the right by the same amount you increase the idle. If you left it stock then the ISC never has a chance to correct until it is to late and then spark control takes over.

800- 672 = 128
Try bumping the entire curve up by 128 RPM.

I also played around with the gain control on the ISC FN860. I believe this is the same as the 'P' in a PID loop.

Clint, I have a A9S, none of these functions are available to me.

What bugs me is how the MAFV can be higher at lower RPM!?

86GT · 09-26-2005, 02:44 PM

I looked at the A9S strategy and it has FN810. It might help. I agree about the weirdness with the higher MAF at lower RPM. What about temp. Is it the same on both idles?

TT331FB · 09-26-2005, 03:41 PM

Quote:

Originally Posted by 86GT

I looked at the A9S strategy and it has FN810. It might help. I agree about the weirdness with the higher MAF at lower RPM. What about temp. Is it the same on both idles?

Clint, What is the name of this function in Tweecer Terms?

86GT · 09-26-2005, 06:23 PM

'ISC adder vs RPM'

If you look down in the lower right corner it will tell you the function number. I usually refer to those because for some reason Mike calles these things something different between stratieges even though they are the same thing.

Disney Lincoln · 09-27-2005, 12:51 AM

How do you raise that a certain RPM??

Mine looks like this:
X 0 0 0 2457.5 16384
Y .03125 .03125 .03125 .033447 .033447

09-26-2005, 08:16 AM	#1
TT331FB Member Join Date: Aug 2005 Posts: 53	TB Air Flow Strangeness A9S, 3" Pro Mass Air 42#, blow through. My tune is pretty good except the motor dies occasionaly comming down to idle. I decided to check TB air flow. I had .46 VDC average MAFV at 600 RPM, ICS disconnected and spout out. I data logged normal idle and got 797 RPM, .45 MAFV average. Huh? Data log shows the idle spark is all over the place. The only thing I can figure is that spark is causing fluctuating MAFV giving an average lower than TB airflow. My plan is to data log idle again but with the spout out to remove the EEC efforts to control idle. Any input? Eric __________________ TT331FB - T3/.6/.63 turbos, Spearco intercooler, 302/331 Mexican Block,AFR 185 heads, 80mm MAF, 75mm TB, 50# injectors, Tweecer, Track Heat intake, Comp cams roller blower grind, MSD BTM, DIY-WB, Yokogawa video display,T-56 tranny, 9" 3.5:1 Traclock, 4x disk brakes, TCP most everything, shelby roll bar. First fire up 2/14/2004.

09-26-2005, 10:06 AM	#3
TT331FB Member Join Date: Aug 2005 Posts: 53	Re: TB Air Flow Strangeness Just for grins, I gonna log idle with ISC connected, spout out. I think the spark is adding instability into the loop. __________________ TT331FB - T3/.6/.63 turbos, Spearco intercooler, 302/331 Mexican Block,AFR 185 heads, 80mm MAF, 75mm TB, 50# injectors, Tweecer, Track Heat intake, Comp cams roller blower grind, MSD BTM, DIY-WB, Yokogawa video display,T-56 tranny, 9" 3.5:1 Traclock, 4x disk brakes, TCP most everything, shelby roll bar. First fire up 2/14/2004.

09-26-2005, 10:50 AM	#4
93Cobra#2771 The Kocky One Join Date: Dec 2004 Location: Yeah, but those cutters won't bust any walnuts.â„¢ Posts: 1,948	Re: TB Air Flow Strangeness It can do that - even spark takes SOME time to change, and it could end up chasing itself to a nice surging, dying tune... __________________ *For Sale: Reproduction Window Stickers, 87+ Mustangs, Cobras, Lightnings, and HD F150!* Richard White 93 Cobra Kocky will be back!

09-26-2005, 10:56 AM	#5
86GT Member Join Date: Mar 2005 Location: Sacramento California Posts: 449	Re: TB Air Flow Strangeness That does seem kind of weird that the normal idle MAF is less than the base idle with ISC disconnected and spout out. From what I have experienced, The ISC will compensate for idle if it is within some calibratable tollerance. I wish I knew the limits. If the desired RPM minus the actual RPM is out side of these limits then spark is used to bring it back into tollerance. I believe the upper limit is set by the scalar ISCLPD. Look at function FN810. It tell the EEC what DC to send to the ISC for a given RPM error. Since your idle has been changed to 800 or so then the FN810 will need to be shifted to the right by the same amount you increase the idle. If you left it stock then the ISC never has a chance to correct until it is to late and then spark control takes over. 800- 672 = 128 Try bumping the entire curve up by 128 RPM. I also played around with the gain control on the ISC FN860. I believe this is the same as the 'P' in a PID loop. __________________ EEC Analyzer A9M, TwEECer, 306ci, 73mm C&L w Tuner Tube, Cobra Intake, 42# inj, Edelbrock 6037, E303 cam, 155 fuel pump, FPR, 70mm TB, E-Fan, 3.55 gears, Powerdyne 9psi actual 5psi...way more.

09-26-2005, 02:44 PM	#7
86GT Member Join Date: Mar 2005 Location: Sacramento California Posts: 449	Re: TB Air Flow Strangeness I looked at the A9S strategy and it has FN810. It might help. I agree about the weirdness with the higher MAF at lower RPM. What about temp. Is it the same on both idles? __________________ EEC Analyzer A9M, TwEECer, 306ci, 73mm C&L w Tuner Tube, Cobra Intake, 42# inj, Edelbrock 6037, E303 cam, 155 fuel pump, FPR, 70mm TB, E-Fan, 3.55 gears, Powerdyne 9psi actual 5psi...way more.

09-26-2005, 08:33 AM	#2
93Cobra#2771 The Kocky One Join Date: Dec 2004 Location: Yeah, but those cutters won't bust any walnuts.â„¢ Posts: 1,948	Re: TB Air Flow Strangeness Your idle spark jumping all over shows your idle is not stable - the EEC uses spark and ISC to control idle, with the quicker reacting spark getting the nodd on a surging idle. More timing equals faster idle, less timing equals slower idle. When coming down to an idle, is this when driving, or when sitting still? Dashpot decay may be something you need to look at... __________________ *For Sale: Reproduction Window Stickers, 87+ Mustangs, Cobras, Lightnings, and HD F150!* Richard White 93 Cobra Kocky will be back!

09-26-2005, 06:23 PM	#9
86GT Member Join Date: Mar 2005 Location: Sacramento California Posts: 449	Re: TB Air Flow Strangeness 'ISC adder vs RPM' If you look down in the lower right corner it will tell you the function number. I usually refer to those because for some reason Mike calles these things something different between stratieges even though they are the same thing. __________________ EEC Analyzer A9M, TwEECer, 306ci, 73mm C&L w Tuner Tube, Cobra Intake, 42# inj, Edelbrock 6037, E303 cam, 155 fuel pump, FPR, 70mm TB, E-Fan, 3.55 gears, Powerdyne 9psi actual 5psi...way more.

09-27-2005, 12:51 AM	#10
Disney Lincoln Senior Member Join Date: May 2005 Posts: 290	Re: TB Air Flow Strangeness How do you raise that a certain RPM?? Mine looks like this: X 0 0 0 2457.5 16384 Y .03125 .03125 .03125 .033447 .033447