Power FC Any way to Log Idle Speed Control Duty Cycle with Datalogit?
02-19-10, 09:00 AM
#2
I'm 90% sure I've found it. It is not properly labeled. It's "Advance ??? (2)"
It is scaled from 0-1000, with 1000 corresponding to 100% duty and 0 corresponding to 0 duty. I was surprised to see that the ISC is still pulsing while the engine is moving and the throttle is open. But this Advance ??? (2) parameter seems to match the reference values in the FSM somewhat:
Now my throttle plate has been adjusted compared to factory so it's unsurprising that it's not perfectly in line with the FSM values. If you do a log of an idle learn procedure you will see this Advance ??? (2) value fluctuating greatly as the PFC tries to stabilize idle. Also, I have logs from a Djetro S14 SR20DET Power FC and it also has the Advance ??? (2) parameter. Its behavior seems to match what I am seeing in the Rx-7 Power FC. During cranking for example the duty is near 100% and then it tapers down.
It is scaled from 0-1000, with 1000 corresponding to 100% duty and 0 corresponding to 0 duty. I was surprised to see that the ISC is still pulsing while the engine is moving and the throttle is open. But this Advance ??? (2) parameter seems to match the reference values in the FSM somewhat:
Now my throttle plate has been adjusted compared to factory so it's unsurprising that it's not perfectly in line with the FSM values. If you do a log of an idle learn procedure you will see this Advance ??? (2) value fluctuating greatly as the PFC tries to stabilize idle. Also, I have logs from a Djetro S14 SR20DET Power FC and it also has the Advance ??? (2) parameter. Its behavior seems to match what I am seeing in the Rx-7 Power FC. During cranking for example the duty is near 100% and then it tapers down.
02-20-10, 10:42 AM
#5
Thank you for the information. I go back to this thread:
https://www.rx7club.com/power-fc-forum-47/idle-fixing-thoughts-867841/
which talks about a strategy to set minimum ISC duty cycle. Don't know if it is even important to run minimum duty but right now I am unsure if I am even close with my air adjustments so I thought an ISC log would give me a clue as to where I am.
Do you know, does the PFC prefer to control idle rpm with air or ignition? It seems like it would be better to control rpm with air rather than retarding the timing. But I don't know if that is possible.
Do you think there is an optimum duty for the ISC? Maybe at 40 or 50% for E Load (the middle load condition)?
Jeff
https://www.rx7club.com/power-fc-forum-47/idle-fixing-thoughts-867841/
which talks about a strategy to set minimum ISC duty cycle. Don't know if it is even important to run minimum duty but right now I am unsure if I am even close with my air adjustments so I thought an ISC log would give me a clue as to where I am.
Do you know, does the PFC prefer to control idle rpm with air or ignition? It seems like it would be better to control rpm with air rather than retarding the timing. But I don't know if that is possible.
Do you think there is an optimum duty for the ISC? Maybe at 40 or 50% for E Load (the middle load condition)?
Jeff
02-20-10, 04:59 PM
#6
That strategy I proposed was before I figured out how to log ISC duty cycle. It was based on some educated guesses about ISC behavior, but I'm not sure all of those were fully correct. Since I literally just figured out how to log ISC duty cycle after you created this thread, we're in somewhat uncharted territory here. If you turn off idle IG control then the PFC will control idle speed using ISC valve duty cycle alone. But so far I've chosen to keep that on for a number of reasons which I have already outlined. I just started looking through ISC valve duty cycle on my recent logs. On my car I just noticed that when E/L comes on, my timing advances and my ISC duty cycle goes to near zero--but I have an unusual setup so that doesn't necessarily mean anything.. It does seems that the PFC like usings timing to control the idle more when it's under E/L, but I can't be sure for A/C because I haven't tested on a car with A/C yet.
Unless you are running completely manual idle control, the PFC will always bump up timing when it receives an ELD, it just won't use a closed loop strategy if the idle IG control is off. One test that I think would be interesting: if you can get access to it, adjust the air adjusting screw under the TB while logging. See how that affects ISC valve duty cycle. My buddy's FD is down and I can't do this test on my personal car because my series 5 intake manifolds and ISC valve have no provision for an air adjusting screw.
I think the range in the service manual makes sense to me. But one of the biggest things to look at is the ISC duty cycle during deceleration. This is when RPMS are decreasing and throttle plate is completely closed (TPS voltage at whatever your closed value is). From limited testing, I've noticed that the ISC duty "hovers" for a second or two when the throttle is closed and rpms are dropping. I figured out a while ago that the F/C settings affect this behavior, but at the time I did not know how to actually log ISC duty.
I know that's kind of rambling but what I'm trying to say is start fiddling with the TB plus the idle and F/C settings, take some logs, and report back.
Unless you are running completely manual idle control, the PFC will always bump up timing when it receives an ELD, it just won't use a closed loop strategy if the idle IG control is off. One test that I think would be interesting: if you can get access to it, adjust the air adjusting screw under the TB while logging. See how that affects ISC valve duty cycle. My buddy's FD is down and I can't do this test on my personal car because my series 5 intake manifolds and ISC valve have no provision for an air adjusting screw.
I think the range in the service manual makes sense to me. But one of the biggest things to look at is the ISC duty cycle during deceleration. This is when RPMS are decreasing and throttle plate is completely closed (TPS voltage at whatever your closed value is). From limited testing, I've noticed that the ISC duty "hovers" for a second or two when the throttle is closed and rpms are dropping. I figured out a while ago that the F/C settings affect this behavior, but at the time I did not know how to actually log ISC duty.
I know that's kind of rambling but what I'm trying to say is start fiddling with the TB plus the idle and F/C settings, take some logs, and report back.
02-21-10, 10:17 PM
#7
Thank you for the reply. Before I try graphing a log and seeing what happens to the ISC I wanted to make sure I have set this up correctly.
So here is a screenshot of my chart and a portion of the log from Microsoft Notepad. It looks like the chart is showing the ??? or ISC data but I'm not sure what it means. Why does the Idle Speed Control duty change all the time, even when the engine is well beyond idle?
And the values in the ? column in the text file don't change. They are all 128. Maybe I just selected the wrong data or set the chart up incorrectly. I have also included a portion of the log file if anyone cares to look at it.
Jeff
So here is a screenshot of my chart and a portion of the log from Microsoft Notepad. It looks like the chart is showing the ??? or ISC data but I'm not sure what it means. Why does the Idle Speed Control duty change all the time, even when the engine is well beyond idle?
And the values in the ? column in the text file don't change. They are all 128. Maybe I just selected the wrong data or set the chart up incorrectly. I have also included a portion of the log file if anyone cares to look at it.
Jeff
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02-22-10, 10:58 AM
#8
Open the logs in Excel as a text delimited file. The column highlighted here is the one you want to look at, it's on the very far right.
Why does the Idle Speed Control duty change all the time, even when the engine is well beyond idle?
I don't have the full log here, but do a chart of TPS voltage, ISC duty, and RPM and you will see what I mean.
02-22-10, 11:51 AM
#9
Thank you for the reply. There are two choices for ??? columns in the pull down menu. Both say the same thing - ???. I guess I picked the correct ??? column to chart but looked at the wrong one in the text file.
If you remember this is a HBP. I don't remember exactly what those idle speeds were set to, but they are around 1060 to 1100 rpm for both No load and E load. AC is a little higher. I know this may be a little low but I want to try to get it to idle in that range. I can always speed it up if necessary. But even without the ISC (and now also since I put one on) the PFC has been able to hold a good steady idle. Only issue so far has been some surging from time to time. I'm just assuming it has to "learn" more as I drive it.
Fuel cut is fairly low. Again I don't remember but probably 1250 to 1300.
What do you suggest I chart for this test? ISC, RPM, IGL, INJ duty?
If you remember this is a HBP. I don't remember exactly what those idle speeds were set to, but they are around 1060 to 1100 rpm for both No load and E load. AC is a little higher. I know this may be a little low but I want to try to get it to idle in that range. I can always speed it up if necessary. But even without the ISC (and now also since I put one on) the PFC has been able to hold a good steady idle. Only issue so far has been some surging from time to time. I'm just assuming it has to "learn" more as I drive it.
Fuel cut is fairly low. Again I don't remember but probably 1250 to 1300.
What do you suggest I chart for this test? ISC, RPM, IGL, INJ duty?
02-23-10, 12:50 AM
#10
I looked through your logs and it showed you already having about an 1100rpm idle. If the problem is surging, then I would chart RPM, ISC, TPS volts, and vehicle speed. Have watches set up for each of those as well as watches for IGL and IGT, plus wideband AFR. Try to narrow down what may be causing the surging. It could be a lean mixture or the rpms just dropping too fast on deceleration. As the idle stumbles the ISC valve may struggle to keep it alive by raising duty cycle, causing a surge.
02-23-10, 10:00 PM
#11
So here is a chart showing idle with no load, electrical load, a/c load (a/c doesn't work but both fans come on when A/C switch is turned on).
Couldn't attach the log, even though it was so short it was still too big a file. Could email it though if anyone wants to see it.
I would have expected ISC duty to increase as it supplies more air but it seems just the opposite - as I added electrical load and then A/C load the duty actually decreased. So maybe the default for the valve is open.
What do think we can make from this? Since I am close to maximum duty for no load should I open the Air Adjusting Screw a little? One thing which may skew the results - the throttle body was open, no elbow on so I could get to the AAS more easily. Even at idle I think there might be a little positive pressure which could increase the amount of air entering the manifold at any given duty.
Let me know what you guys think.
Jeff
Couldn't attach the log, even though it was so short it was still too big a file. Could email it though if anyone wants to see it.
I would have expected ISC duty to increase as it supplies more air but it seems just the opposite - as I added electrical load and then A/C load the duty actually decreased. So maybe the default for the valve is open.
What do think we can make from this? Since I am close to maximum duty for no load should I open the Air Adjusting Screw a little? One thing which may skew the results - the throttle body was open, no elbow on so I could get to the AAS more easily. Even at idle I think there might be a little positive pressure which could increase the amount of air entering the manifold at any given duty.
Let me know what you guys think.
Jeff
02-23-10, 10:19 PM
#12
I might have mis-interpreted those graphs in my earlier post. Maybe higher duty really is more air. It looks like as the load increases the timing advances and the AFR actually gets richer which could mean the ISC is cutting back some air.
arghx?
arghx?
02-24-10, 08:45 AM
#13
Next time you take a screenshot, do not shrink it. Just post it full size so everything isn't so small.
One thing I myself have noticed is that the PFC prefers to control idle with ignition timing rather than ISC duty when the idle is under load, as you have noted. More ISC duty = more air bypassing the throttle plates, and the opposite is also true. You can see the ISC duty progressively stepping down and the ignition timing increasing. Unfortunately you don't have a log of you encountering any actual idle problems (stumbles, surges, etc). And so there's only so much I can help you with. A high ISC valve duty cycle at no-load idle isn't automatically a problem--meaning, if the car drives fine just leave it alone (if it ain't broke, don't fix it type of deal).
But you indicate some stumbling or surging at times, I presume on deceleration. When does it occur, because I don't see it here? With no load, electrical load, a/c load? all three? Can you please attempt to recreate whatever's been happening and log it? That's the best thing for you to do right now. Recreate the problem and log it. And when you log it, make sure you have only "Advance" and "Aux A/D" checked under the monitor window so that you have a faster sample rate than the 10ish samples per second you have right now. You can see your sample rate by loading up the Power FC log in Excel and counting how many timestamps per second in the leftmost column.
One thing I myself have noticed is that the PFC prefers to control idle with ignition timing rather than ISC duty when the idle is under load, as you have noted. More ISC duty = more air bypassing the throttle plates, and the opposite is also true. You can see the ISC duty progressively stepping down and the ignition timing increasing. Unfortunately you don't have a log of you encountering any actual idle problems (stumbles, surges, etc). And so there's only so much I can help you with. A high ISC valve duty cycle at no-load idle isn't automatically a problem--meaning, if the car drives fine just leave it alone (if it ain't broke, don't fix it type of deal).
But you indicate some stumbling or surging at times, I presume on deceleration. When does it occur, because I don't see it here? With no load, electrical load, a/c load? all three? Can you please attempt to recreate whatever's been happening and log it? That's the best thing for you to do right now. Recreate the problem and log it. And when you log it, make sure you have only "Advance" and "Aux A/D" checked under the monitor window so that you have a faster sample rate than the 10ish samples per second you have right now. You can see your sample rate by loading up the Power FC log in Excel and counting how many timestamps per second in the leftmost column.
02-24-10, 11:56 AM
#14
Thanks for looking at this. You're correct, last night when I took this log I couldn't get it to surge. That's what the two throttle blips were about, to see if it would keep the rpms up for awhile, but they dropped down immediately.
When it has happened it seems to happen earlier in the warmup phase, even though the fast idle has disengaged. I just figured maybe it was "learning" to idle better and would teach itself to not do that - kind of like when it goes through the idle learn process.
Speaking of which, how do you make it go through idle learn again. I tried disconnecting the battery terminal and holding the brake down for a little bit and I tried "re-initialize" off of the ETC menu (and reloading the map right away) but neither seemed to go into the extensive routine that it did the first time. Maybe relearn would help if the surging continues.
Main thing is it looks like my AAS and Idle Adjustment Screw are within the ISC range of operation so maybe I'm good there.
I know this idle is a little slow for a HBP, sometimes when I blip the throttle I get a pop in the exhaust. Is there an adjustment I should make for that? I think I have increased the TPS vs INJ setting a little bit.
Thanks again.
When it has happened it seems to happen earlier in the warmup phase, even though the fast idle has disengaged. I just figured maybe it was "learning" to idle better and would teach itself to not do that - kind of like when it goes through the idle learn process.
Speaking of which, how do you make it go through idle learn again. I tried disconnecting the battery terminal and holding the brake down for a little bit and I tried "re-initialize" off of the ETC menu (and reloading the map right away) but neither seemed to go into the extensive routine that it did the first time. Maybe relearn would help if the surging continues.
Main thing is it looks like my AAS and Idle Adjustment Screw are within the ISC range of operation so maybe I'm good there.
I know this idle is a little slow for a HBP, sometimes when I blip the throttle I get a pop in the exhaust. Is there an adjustment I should make for that? I think I have increased the TPS vs INJ setting a little bit.
Thanks again.
02-24-10, 06:13 PM
#15
technically your TPS is out of spec for the idle range. Your VTA2 narrow range sensor is over 1 volt (check the logs). I'm not sure if that's doing anything or not. To make it go through idle learn, first save your map in the datalogit. Then initialize the ECU either in the datalogit software or in the commander. Turn the key off, then turn it back on. Reload the map. Then start the engine.
I'd have to see a log of it. But I can say right now that I feel you have very high expectations for a bridgeport. No offense, but you sound like you have "bridgeport remorse." Most people who put a huge cam in their 'maro or Corvette are proud of those kinds of noises...
sometimes when I blip the throttle I get a pop in the exhaust. Is there an adjustment I should make for that? I think I have increased the TPS vs INJ setting a little bit.
03-01-10, 10:34 AM
#16
technically your TPS is out of spec for the idle range. Your VTA2 narrow range sensor is over 1 volt (check the logs). I'm not sure if that's doing anything or not. To make it go through idle learn, first save your map in the datalogit. Then initialize the ECU either in the datalogit software or in the commander. Turn the key off, then turn it back on. Reload the map. Then start the engine.
I'd have to see a log of it. But I can say right now that I feel you have very high expectations for a bridgeport. No offense, but you sound like you have "bridgeport remorse." Most people who put a huge cam in their 'maro or Corvette are proud of those kinds of noises...
I'd have to see a log of it. But I can say right now that I feel you have very high expectations for a bridgeport. No offense, but you sound like you have "bridgeport remorse." Most people who put a huge cam in their 'maro or Corvette are proud of those kinds of noises...
Have I lost anything if I have the PFC "relearn" at this point? I was thinking that as you drive it it fine tunes itself as time goes by. It is getting much better. When fully warmed up it drops down to the idle speed specified in the PFC and holds it pretty well.
But here's an idea I had. Based on what I have been seeing when under No Load the PFC is severely retarding timing and upping air to hold the idle setpoint. You can really hear the difference in the exhaust between No Load idle and E/Load idle. At E Load the timing advances dramatically, air goes down some, but it just sounds more healthy. By watching the monitor screen I can see when E Load and AC/Load come on by the check boxes. All it takes is to turn the running lights on for E/Load. So why not trick the PFC into thinking it is running in E/Load all the time (or at least until AC/Load comes on)? I can't see a downside to this. I have my idle speeds set the same for E/Load (actually 10 rpm less) and the PFC holds idle rpm very well as I toggle between the two.
What do you think? Maybe I should drive around with my running lights on for awhile and see how it does.
BTW - Not at the "remorse" stage yet but could get there. However, it is what it is. This is the engine that came in my car when I bought it so if I can't get it to run the way I like I'll just eventually replace it. I will say though, the HBP exhaust sound is just as cool as my old '65 with the Duntov cam.
03-01-10, 05:39 PM
#17
In your situation the easiest way to add timing under no load is to raise the no load idle speed. You may end up having a no load target idle speed that is higher than your E/L or A/C speed. There's nothing wrong with that, I actually have that on my car. Once the engine is fully warmed up and no electrical load is applied, go into the idle speed setting screen on the commander. Raise the Idle A.E. setting. You can take logs, but I would initially adjust it by ear with the Commander. The commander allows you to make very quick adjustments which helps for that. Fuel cut speeds may also need to be adjusted.
With a large streetport my target idle speeds are
1000 AE
950 E/L
950 A/C
actual no load idle speed is about 900-950, while electrical load idle speed is 950-1000. The engine pulls about 13 inches of vacuum at that speed (330 mm Hg on the Commander with a calibrated GM 3 bar MAP sensor). So try something like
1200 AE
1100 EL (or whatever speed it is set to now)
1100 A/C
and raise your AE F/C speed if necessary. Try raising the base idle speed higher than that if you have to. As you can see, you just have to fiddle with it until you are happy with the final result.
With a large streetport my target idle speeds are
1000 AE
950 E/L
950 A/C
actual no load idle speed is about 900-950, while electrical load idle speed is 950-1000. The engine pulls about 13 inches of vacuum at that speed (330 mm Hg on the Commander with a calibrated GM 3 bar MAP sensor). So try something like
1200 AE
1100 EL (or whatever speed it is set to now)
1100 A/C
and raise your AE F/C speed if necessary. Try raising the base idle speed higher than that if you have to. As you can see, you just have to fiddle with it until you are happy with the final result.
03-01-10, 06:11 PM
#18
With a large streetport my target idle speeds are
1000 AE
950 E/L
950 A/C
actual no load idle speed is about 900-950, while electrical load idle speed is 950-1000. The engine pulls about 13 inches of vacuum at that speed (330 mm Hg on the Commander with a calibrated GM 3 bar MAP sensor). So try something like
1200 AE
1100 EL (or whatever speed it is set to now)
1100 A/C
and raise your AE F/C speed if necessary. Try raising the base idle speed higher than that if you have to. As you can see, you just have to fiddle with it until you are happy with the final result.
And how do you get your actual idle speeds to be so much less than the targets?
What I was suggesting earlier was a bit of a compromise between the PFC controlling idle and manual idle control. I don't think the PFC is reacting to any actual loading condition on the engine such as increased alternator output, it is switching idle loads and speeds based only whether it reads a switch open or closed. Rather than having 3 idle speeds which is what the PFC now has, by eliminating the No Load speed the remaining two speeds seem to run the most advanced timing and thus the "cleaner" idle. Anyway just a thought.
Like I said before, I can live with the idle I have right now, I am just fascinated by this PFC and like to learn more about how it works.
03-02-10, 12:18 AM
#19
I seem to be missing something. I thought No Load was to be the lowest of the three rpms, followed by E Load and then A/C Load. Yet you are suggesting the reverse. Does that mean that your highest idle speed is with No Load?
And how do you get your actual idle speeds to be so much less than the targets?
And how do you get your actual idle speeds to be so much less than the targets?
Advanced Idle Troubleshooting - Idle IG control
Based on your settings in the etc. --> function select menu, the PFC controls idle with the following logic:
1. O2 feedback and Idle IG Control ON (default): PFC controls idle fuel based on factory O2 sensor signal, PFC uses closed loop idle control. Neither fuel nor timing are directly adjustable by the user.
2. O2 feedback OFF, Idle IG control ON: User can control fuel, closed loop fuel is disabled completely, PFC varies idle timing in an effort to reach target idle speeds. Turning off O2 feedback is usually necessary on cars without an airpump.
3. O2 feedback OFF, Idle IG control OFF: Ignition timing is fixed at
-5 L, -20 T for no load idle, same as the FC and FD service manual spec and same as the yellow and red timing marks on the FC crank pulley
4 L, -6 T for electrical load idle. electrical load is triggered by either engaging the fans (fan output) or by the PFC receiving a signal from the electrical load detection computer (ELD input)
I don't know the fixed A/C ignition timing values off the top of my head.
The ignition timing is completely static for the three idle conditions (no load, fans or electrical load applied, A/C load). The PFC manual specifically states that turning off Idle IG control was intended for checking ignition timing with a timing light. On an FD that's not normally necessary, although it is on an FC because the crank angle sensor is installed like a distributor.
4. O2 feedback OFF, Idle IG control OFF, idle speeds set to 0. This is what many refer to as "manual idle control," and can only be enabled with a Datalogit. The user has complete control over idle ignition timing but the ISC valve no longer functions for A/C or E/L idle up or improved cold starting. There are advantages and disadvantages to this configuration, and all I will say is that using this depends on your setup and your personal preferences. PM Chuck Westbrook (cewrx7r1) about tuning notes, I won't go into it much because this thread is all about Commander tuning.
With an ISC installed and no airpump, I personally prefer to have O2 feedback OFF and Idle IG control ON. Now let's discuss steady state (not decelerating or free revving) idle speed control before we get to the very thorny issue of deceleration idle problems.
With Idle IG control ON, the PFC calculates ignition timing in this basic way:
base idle ignition timing (a separate value for no load, electrical load, or A/C) + closed loop correction factor
The closed loop correction factor is somehow calculated by measuring how far the current speed differs from its target, or the "error" term for those of you with any knowledge of closed loop jargon. With idle IG control on, the PFC will vary the ignition timing within some range of authority in order to stabilize engine vacuum and get closer to the target idle speed. The PFC will also add more idle air through the ISC valve when electrical or A/C load are applied, even if they have the exact same target idle speeds.
The PFC will advance ignition timing to raise the idle speed or retard ignition timing to lower the idle speed. While it is not possible to directly set idle ignition timing without full manual idle control, a little fiddling with the idle settings will accomplish the same goal. As counterintuitive as it may seem, my current idle speeds are:
1000rpm no load
950 rpm E/L
950 rpm A/C (no A/C is installed on my 2nd gen but I have tuned A/C idle before)
Yet with my throttlebody adjustments, I actually idle at around 900rpm with no load or electrical load applied. Basically I adjusted the idle through the TB down (in order to prevent idle sticking on decel) then effectively raised the base idle speed through indirectly manipulating the PFC's ignition timing logic. Note that this is on an engine with large intake and exhaust ports that pulls very little vacuum for a non-bridge engine. The work-arounds and manipulations I have done are probably not necessary on most people's setups. You need to remember that The PFC and the throttlebody adjustment all work together to control idle speed under various driving conditions.
Based on your settings in the etc. --> function select menu, the PFC controls idle with the following logic:
1. O2 feedback and Idle IG Control ON (default): PFC controls idle fuel based on factory O2 sensor signal, PFC uses closed loop idle control. Neither fuel nor timing are directly adjustable by the user.
2. O2 feedback OFF, Idle IG control ON: User can control fuel, closed loop fuel is disabled completely, PFC varies idle timing in an effort to reach target idle speeds. Turning off O2 feedback is usually necessary on cars without an airpump.
3. O2 feedback OFF, Idle IG control OFF: Ignition timing is fixed at
-5 L, -20 T for no load idle, same as the FC and FD service manual spec and same as the yellow and red timing marks on the FC crank pulley
4 L, -6 T for electrical load idle. electrical load is triggered by either engaging the fans (fan output) or by the PFC receiving a signal from the electrical load detection computer (ELD input)
I don't know the fixed A/C ignition timing values off the top of my head.
The ignition timing is completely static for the three idle conditions (no load, fans or electrical load applied, A/C load). The PFC manual specifically states that turning off Idle IG control was intended for checking ignition timing with a timing light. On an FD that's not normally necessary, although it is on an FC because the crank angle sensor is installed like a distributor.
4. O2 feedback OFF, Idle IG control OFF, idle speeds set to 0. This is what many refer to as "manual idle control," and can only be enabled with a Datalogit. The user has complete control over idle ignition timing but the ISC valve no longer functions for A/C or E/L idle up or improved cold starting. There are advantages and disadvantages to this configuration, and all I will say is that using this depends on your setup and your personal preferences. PM Chuck Westbrook (cewrx7r1) about tuning notes, I won't go into it much because this thread is all about Commander tuning.
With an ISC installed and no airpump, I personally prefer to have O2 feedback OFF and Idle IG control ON. Now let's discuss steady state (not decelerating or free revving) idle speed control before we get to the very thorny issue of deceleration idle problems.
With Idle IG control ON, the PFC calculates ignition timing in this basic way:
base idle ignition timing (a separate value for no load, electrical load, or A/C) + closed loop correction factor
The closed loop correction factor is somehow calculated by measuring how far the current speed differs from its target, or the "error" term for those of you with any knowledge of closed loop jargon. With idle IG control on, the PFC will vary the ignition timing within some range of authority in order to stabilize engine vacuum and get closer to the target idle speed. The PFC will also add more idle air through the ISC valve when electrical or A/C load are applied, even if they have the exact same target idle speeds.
The PFC will advance ignition timing to raise the idle speed or retard ignition timing to lower the idle speed. While it is not possible to directly set idle ignition timing without full manual idle control, a little fiddling with the idle settings will accomplish the same goal. As counterintuitive as it may seem, my current idle speeds are:
1000rpm no load
950 rpm E/L
950 rpm A/C (no A/C is installed on my 2nd gen but I have tuned A/C idle before)
Yet with my throttlebody adjustments, I actually idle at around 900rpm with no load or electrical load applied. Basically I adjusted the idle through the TB down (in order to prevent idle sticking on decel) then effectively raised the base idle speed through indirectly manipulating the PFC's ignition timing logic. Note that this is on an engine with large intake and exhaust ports that pulls very little vacuum for a non-bridge engine. The work-arounds and manipulations I have done are probably not necessary on most people's setups. You need to remember that The PFC and the throttlebody adjustment all work together to control idle speed under various driving conditions.
Originally Posted by milano maroon
What I was suggesting earlier was a bit of a compromise between the PFC controlling idle and manual idle control. I don't think the PFC is reacting to any actual loading condition on the engine such as increased alternator output, it is switching idle loads and speeds based only whether it reads a switch open or closed.
1) the PFC triggers the #2 and #4 fan relays at the trigger temps set in the Datalogit. The ELD indicator will come on when the fans trigger even if the ELD computer is unplugged, I have personally tested this.
2) a signal is received from the ELD computer. The ELD computer will send the signal when the blower motor switch is on the highest setting, the headlights are engaged, or the defroster is engaged.
The A/C idle mode comes on when the A/C indicator lights up under Sensor/switch check. That's all there is to it.
Rather than having 3 idle speeds which is what the PFC now has, by eliminating the No Load speed the remaining two speeds seem to run the most advanced timing and thus the "cleaner" idle. Anyway just a thought.
03-02-10, 12:43 PM
#20
"The PFC will advance ignition timing to raise the idle speed or retard ignition timing to lower the idle speed. While it is not possible to directly set idle ignition timing without full manual idle control, a little fiddling with the idle settings will accomplish the same goal. As counterintuitive as it may seem, my current idle speeds are:
1000rpm no load
950 rpm E/L
950 rpm A/C (no A/C is installed on my 2nd gen but I have tuned A/C idle before)
Yet with my throttlebody adjustments, I actually idle at around 900rpm with no load or electrical load applied. Basically I adjusted the idle through the TB down (in order to prevent idle sticking on decel) then effectively raised the base idle speed through indirectly manipulating the PFC's ignition timing logic. Note that this is on an engine with large intake and exhaust ports that pulls very little vacuum for a non-bridge engine. The work-arounds and manipulations I have done are probably not necessary on most people's setups. You need to remember that The PFC and the throttlebody adjustment all work together to control idle speed under various driving conditions."
This is the part I don't understand - If you are running an ISC how can you adjust idle speed by adjustments on the throttle body? If you decrease idle speed by limiting air through the Idle Adjustment Screw or the Air Adjustment Screw won't the ISC try to make up for it to reach the amount required to idle at the specified speed?
Are you limiting the amount of air into the throttle body and the ISC at full duty so that the PFC has to increase timing to reach the specified speed?
And then, does that mean that it has maxed out air and advanced timing as much as it can and still the idle is less than requested in the PFC?
1000rpm no load
950 rpm E/L
950 rpm A/C (no A/C is installed on my 2nd gen but I have tuned A/C idle before)
Yet with my throttlebody adjustments, I actually idle at around 900rpm with no load or electrical load applied. Basically I adjusted the idle through the TB down (in order to prevent idle sticking on decel) then effectively raised the base idle speed through indirectly manipulating the PFC's ignition timing logic. Note that this is on an engine with large intake and exhaust ports that pulls very little vacuum for a non-bridge engine. The work-arounds and manipulations I have done are probably not necessary on most people's setups. You need to remember that The PFC and the throttlebody adjustment all work together to control idle speed under various driving conditions."
This is the part I don't understand - If you are running an ISC how can you adjust idle speed by adjustments on the throttle body? If you decrease idle speed by limiting air through the Idle Adjustment Screw or the Air Adjustment Screw won't the ISC try to make up for it to reach the amount required to idle at the specified speed?
Are you limiting the amount of air into the throttle body and the ISC at full duty so that the PFC has to increase timing to reach the specified speed?
And then, does that mean that it has maxed out air and advanced timing as much as it can and still the idle is less than requested in the PFC?
03-02-10, 04:05 PM
#21
This is the part I don't understand - If you are running an ISC how can you adjust idle speed by adjustments on the throttle body? If you decrease idle speed by limiting air through the Idle Adjustment Screw or the Air Adjustment Screw won't the ISC try to make up for it to reach the amount required to idle at the specified speed?
Are you limiting the amount of air into the throttle body and the ISC at full duty so that the PFC has to increase timing to reach the specified speed?
And then, does that mean that it has maxed out air and advanced timing as much as it can and still the idle is less than requested in the PFC?
Are you limiting the amount of air into the throttle body and the ISC at full duty so that the PFC has to increase timing to reach the specified speed?
And then, does that mean that it has maxed out air and advanced timing as much as it can and still the idle is less than requested in the PFC?
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