First of all, I very much regret not getting the DSMlink. The pocketlogger/SAFC combo sucks for the 2G's. You are basically guessing wheather you are knocking by looking at the timing curve. Which is only consistant at WOT.

The problem I am having is that WOT i can get a good timing curve to see if I am knocking. But at part throttle, everytime you go from say 40% throttle to say 60% throttle the ECU sees more air and pulls timing. So I cant tell if it is pulling timing from the gush of air or from knock due to bad part throttle tuning.

Anyways the "proper" 2G timing curve is that at WOT (or any significant amount of throttle) it should drop to about 10 deg and have a very linear straight line to about 20deg. With no drops. This indicates that you are not knocking.

Interesting to note that the 1G timing curve it seems most people get a tip-in timing of about 15 deg and then goes up to 20 deg.

I know that the ecu uses internal maps to determine timing. What exactly are these maps based on?

My guess would be throttle,rpm, karman HZ, intake temp, coolant temp, and engine load. Is this right. And does anybody have any info on these maps?

I have also heard that the ecu will pull 1 deg if your intake temperature is above 85 degrees and 1 deg if your coolant temperature is above 205 degrees.

Now to the S-AFC

The big problem I see is the following:
When tuning the S-AFC you typically want to get the LOW settings to be used for your closed loop operation and your HI settings for your openloop operation. Ideally you would want the SAFC high settings to take over at exactly the same point that your ecu switches to open loop. But this is impossible because the triggering of open loop is not just throttle based. Since the low setting is usually about 5-8 % richer than your hi setting, this becomes a problem. My car goes into open loop alot quicker in 1st gear than in 4th.

Can anybody address these issues?

Thanks

Originally posted by DCJ98GST

Anyways the "proper" 2G timing curve is that at WOT (or any significant amount of throttle) it should drop to about 10 deg and have a very linear straight line to about 20deg. With no drops. This indicates that you are not knocking.

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Actually, the stock map for the 2G would go to only around 14 degrees at WOT, as long as you are flowing a good bit more air than stock. Its really hard to see that in the regular loggers though, you are right. Maybe if you exported your data into a spreadsheet, you might be able to make more sense of it.

Originally posted by DCJ98GST

I know that the ecu uses internal maps to determine timing. What exactly are these maps based on?

My guess would be throttle,rpm, karman HZ, intake temp, coolant temp, and engine load. Is this right. And does anybody have any info on these maps?

Click to expand...

The timing map and fuel map are indexed by airflow per engine revolution, and RPM.
Thats it. Airflow is based on the MAF Hz, the intake temp, and the intake baro pressure.

Originally posted by DCJ98GST

I have also heard that the ecu will pull 1 deg if your intake temperature is above 85 degrees and 1 deg if your coolant temperature is above 205 degrees.

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Yes, and if your intake temp is below a certain value(somewhere around freezing), it pulls a degree, and if the coolant temp gets even higher than that(somewhere around 220, I forget exactly)it pulls 2 degrees.

Personally, if I were tuning an AFC, I wouldnt stress as much about trying to get it to transition at the exact same time the ECU does. Its a piggyback, if you wanted precision, you should have gotten a standalone, and bought a few weeks of dyno time . I think the ECU switches to open loop based mainly on throttle position(somewhere in the 80% range), so you should be able to set some Lo/Hi throttle breakpoints that match that. Alternatively, you could switch between the two maps based off of a GM MAP sensor instead of using the TPS.

Brad:

Originally posted by brads


Actually, the stock map for the 2G would go to only around 14 degrees at WOT, as long as you are flowing a good bit more air than stock.

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Are you saying that the tip-in timing on the map should only go to 14 deg at the best case not 10 deg? Most 2G people see 10deg at tip-in if they are lucky; so is that missing 4 deg due to knock?

Originally posted by brads


The timing map and fuel map are indexed by airflow per engine revolution, and RPM.
Thats it. Airflow is based on the MAF Hz, the intake temp, and the intake baro pressure.

Click to expand...

So why does it pull timing when I go from 40% throttle to say 80%. It is almost like the ecu is shocked by the rapid change in airflow and pulls timing. But when I keep say a steady 80% throttle (steady airflow) it advances normally. This happens at any rpm that I substantially increase throttle.

Originally posted by brads


I think the ECU switches to open loop based mainly on throttle position(somewhere in the 80% range), so you should be able to set some Lo/Hi throttle breakpoints that match that.

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Yea that is the problem, at say 70% throttle you are still at closed loop and flowing more air than at 40% throttle but the AFC is leaner at 70 than 40 so it is kindof counterintuitive.

My lo settings are about 8% richer than my high settings. Typically you want your low settings so that the LTFT is 0. But is there any harm in letting leaning out my Low settings and let my LTFT go to +8. That way the LOW and hi will be closer and more accurate. So letting the LTFT go higher, the ecu is internalizing and accounting for the airflow by storing it in the LTFT. Or would one lose throttle response if LTFT is not at 0.

I think I may eventually go with DSMLink but right now I want to see if I can tune the best I can with this set up. And at least learn how to do it right for my own information.

Thanks for your help

Originally posted by DCJ98GST


Are you saying that the tip-in timing on the map should only go to 14 deg at the best case not 10 deg? Most 2G people see 10deg at tip-in if they are lucky; so is that missing 4 deg due to knock?

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No, the 14 degree is the high RPM timing they'd hit, not the 20 you are talking about. The 2G timing falls to well below 10 at tip in if you are flowing lots of air in the mid RPMs. If you are hitting 20s at high RPMs, that means you are somewhere in the middle of the table.

Originally posted by DCJ98GST

So why does it pull timing when I go from 40% throttle to say 80%. It is almost like the ecu is shocked by the rapid change in airflow and pulls timing. But when I keep say a steady 80% throttle (steady airflow) it advances normally. This happens at any rpm that I substantially increase throttle.

Click to expand...

The way the table is set up, if you keep a steady airflow per engine revolution, the timing goes up as RPMs go up. If you increase your airflow per engine revolution, timing generally goes down. Going from 40% to 80% throttle usually increases the airflow per engine revolution.

Originally posted by DCJ98GST

Yea that is the problem, at say 70% throttle you are still at closed loop and flowing more air than at 40% throttle but the AFC is leaner at 70 than 40 so it is kindof counterintuitive.

My lo settings are about 8% richer than my high settings. Typically you want your low settings so that the LTFT is 0. But is there any harm in letting leaning out my Low settings and let my LTFT go to +8. That way the LOW and hi will be closer and more accurate. So letting the LTFT go higher, the ecu is internalizing and accounting for the airflow by storing it in the LTFT. Or would one lose throttle response if LTFT is not at 0.

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I don't really see the dilemma here. You won't lose throttle response if LTFT is not at 0. Its a good idea to keep the LTFTs closer to zero though, because it gives you more headroom. Putting them at +8 means the ECU will only be able to add a little more fuel if something else goes wrong.

When you hit open loop, the target AF ratio varies based on rpm and airflow per engine revolution. Airflow per engine revolution can almost be viewed as a boost level, even though it isnt quite. So you can look at your open loop fuel enrichment table as rpm vs boost. Knowing this, it might make more sense to try to make the Hi and Lo settings on your AFC vary based on boost, instead of TPS. This way the AFC adjustment table overlays onto the WOT fuel table a little more simply. Under low boost conditions, the target AFR is 14.7:1 in that open loop fuel table anyhow. So that would make it easier to tune it to get the smooth transition that you are looking for.

Brad

Brad, the problem is thus:

The ECU, as you said, has fuel and timing maps indexed by AIRFLOW. However, the SAFC indexes the correction factors by throttle position, which is only a VERY vague indication of true airflow. In different situations, you can have wildly different amounts of load, at the same throttle position (different gears, hills, boost, no boost, etc).

That I am using with my SAFC is a 3-bar MAP sensor. The 3-bar MAP sensor is a 0-5v output just like the TPS, but it is a much better indicator of load than the throttle position. All you have to do is set the low throttle point right around atmospheric pressure (~30% throttle with a 3-bar) and then you set the high throttle point to full boost, or a boost level you will always be at or above at full boost, but only under WOT. I'm going to use about 15 psi, which is around 66% throttle with the 3-bar MAP sensor.

This way, if you have a constant throttle position, but the load increases, the SAFC will change the correction factor.

You can also change the lo settings to have them more closely match the high settings, because the fuel trims will help to offset this if it is within the range of the ECU. This is not nearly as nice a fix though.


....Kyle T.

Originally posted by kpt4321
Brad, the problem is thus:

The ECU, as you said, has fuel and timing maps indexed by AIRFLOW. However, the SAFC indexes the correction factors by throttle position, which is only a VERY vague indication of true airflow. In different situations, you can have wildly different amounts of load, at the same throttle position (different gears, hills, boost, no boost, etc).

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Not airflow, airflow per engine rev, there is a difference. The airflow per engine rev is like a pressure sensor-less guess at boost levels. Thats why I was saying using a MAP sensor like you described would work better with the ECU maps. It allows you to set a high and low adjustment map that come close to fitting what the ECU has. Downside is that if you arent in open loop, but above the Lo-Thr point(0 PSI in your case), it will probably results in changing your fuel trims as the correction factor changes. But like I said, its a piggyback, if its off a little here or there, I wouldnt worry about it. If you want more precision, it costs more.

If you had to stick with TPS, try moving the Lo-Thr point up closer to where the ECU transitions to open loop.

Brad

So timing is advanced only due to the amout of air the ECU sees per rpm. And the pocketlogger reads directly what the airflow the ECU is seeing in LBS/min. This is exactly what the ecu sees after the S-AFC adjustments and all the temperature and pressure is taken into account. And this can be logged with the pockelogger per rpm and timing.

Now the only thing left is to determine is what the ECU maps are. Now with all this information, we should be able to directly determine if there is any knock retard.

Right?

Example:

Say I am getting 24 lbs/min between 3000 rpm and 5500 rpm and 20 lbs/min from 5500 rpm and 6500 rpm (due to t-25 drop off).

There should be a direct timing degrees for each rpm point on the map for the respecive lbs/min. If my timing matches this, then I am not knocking. If it is less, than I am knocking at that rpm.

Originally posted by DCJ98GST

Now the only thing left is to determine is what the ECU maps are. Now with all this information, we should be able to directly determine if there is any knock retard.

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Yep. thats pretty much it. Because the ecu extrapolates between RPMs and airflow levels, you will have to do that once you figure out the stock timing table.

Brad

Originally posted by brads


Yep. thats pretty much it. Because the ecu extrapolates between RPMs and airflow levels, you will have to do that once you figure out the stock timing table.

Brad

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So what would be the best way to get these tables?