I've been working in 32B trying to get dead cold starts to idle more smoothly and wanted to ask what the true intention of this table is. Is it to act like a choke, or is it to get the catalytic converter fired up and ready? If the latter then I'll just zero it out as I have no cat in the vehicle.

Comparing BINs like ABTB (32B) to ARAP or APYP (6E) (87 Corvette vs. 89 Corvette) shows very drastic differences.

ABTB never gets below 45% change and is as high as 69% at -40* (F).

APYP is as low as 9.77% change for 68* (F) or higher, but is as high as 60% at -40* (F).

I've already modified my 32B to use the crank fueling of 6E as I've removed my cold start injector due to a superram intake manifold.

I'm also curious what the #s directly translate into. If the ECM would normally be commanding a 2.0ms pulsewidth and it sees 10% in this table is it as simple as then executing a 2.2ms pulsewidth?

Thank you in advance for any insight, my searches haven't really come up with any concrete answers on this one even though it seems like a common table.

 

I believe it's allowing lower temperatures to have a specified richer AFR than when hotter temps. Fuel doesn't atomize as well when cold, so you need more of it. It's temperature based for open loop, as you aren't in full use of all the tables as when closed loop occurs.

Can't go beyond that in my limited knowledge.

 

It definitely makes sense to work that way; I really would love to dig into how it is applied. For example does it look at the stoich ratio in your BIN and adjust it down the higher the % in the table is?

 

Open Loop means the ECM is using the VE table as the basis of fueling without other intervention. With the O2 sensor requiring heat up time, fueling is approximated. The AFR% change table applies the % modifier to the VE table until parameters meet the criteria for Closed Loop operation. Given that the ECM utilizes the base VE table for O/L,
the AFR% can vary quite a bit from one calibration to the next.

 

That being the case, It would appear that fiddling with the lower VE table in particular (lower because we are warming up in park) would affect the overall AFR in open loop, since the % modifier is acting off of that chart.

I would gauge that if you have made major changes in the lower VE table then needing to alter the % modifier table would make sense.

 

You got it.

 

I know what open loop is, there was no question about that. Sorry if the original post somehow did not make that clear. I'm also dealing with a MAF system and not speed density where I believe the VE tables come into play.

So back to the original question... choke effect or cat warming; I'd say we're still learning towards the choke effect.

I just find it hard to believe a stock vehicle was dumping anywhere from 45%-70% more fuel into the engine without leaving a black fog behind it, which is why I'm trying to learn how/where the value is applied.

 

I've not worked with MAF systems, but isn't the primary diff between the two
that MAF provides a direct reading of airflow whereas SD interpolates it?
In either case, that gets used to determine how much fuel to meter and that there is a base map for fuel? If so, then the AFR% change table is still used to
modify the base fuel metering(however calc'd) resulting in a richer (choked) mixture. I think you certainly want to heat up the cat asap, but the motor needs to run first. With a cold motor, that means more fuel till you reach operating temps. Again, apologies if I am being too basic.

 

No no that's fine, and it is good for others that find the thread later on. It's just one of those tables that sounds so simple, but where/how it is applied appears to be a littel bit of a mystery. I'll dig around in the HAC some more and see if there is any evidence.

 

Scorp,

I have used it on the 7747, EBL and now the LT-5 calibrations to modify AFR mostly for warm-up idle purposes. It has come in handy especially now that my LT-5 has larger intake cams. Combination of VE table and AFR O/L table for warm up idle tuning.

 

This might answer some of my own questions that I've had with hot restart issues.
My afr's have been going very lean, maxed at 20, and seeing a check engine light while in open loop until closed loop hits and it goes back to normal.

I've been leaning out my open lower fuel table to correct for a rich closed loop idle. Probably cut by 10 % over the past month, and the check engine and high AFR have only begun recently.

It finally makes sense that I need to enrichen the choke affect, that being based on a % modifier from the lower VE table, it needs to be raised to compensate for the fact I've lowered what it's derived and reading from!

AMAZING! I'm actually starting to get some of this stuff!


Dave
Rochester NY


.

 

When in open loop, in $32, $6E, and $8D (among others), the stoich AFR value is adjusted for load and coolant temperature. It is a percent change to stoich to create the commanded AFR.

The commanded AFR is used in the PW calculation, thereby changing the PW according to the desired AFR.

RBob.

 

So does that mean we are on the right track or that I still don't have a clue?

I should find my Commanded AFR for open loop, maybe consider raising that?
or was I correct in thinking raising my % modifier to temp as the way to end hot restart lean outs? (yes, I'm in $8d) I didn't catch the implication of your information.

Dave

 

I'm not sure if you are getting it or not. The VE table should be adjusted on a warmed up engine. Then left alone.

When in open loop, if the AFR is too rich or too lean, you adjust it by using the open loop modifiers tables that act on the stoich AFR.

scorp508: "I've been working in 32B trying to get dead cold starts to idle more smoothly and wanted to ask what the true intention of this table is. Is it to act like a choke, or is it to get the catalytic converter fired up and ready? "

It is a choke table. Commands a richer AFR on a colder engine. Don't confuse this with after start fuel, which is usually called choke fuel.

To kick the cat-con off, see the SA CTS/LV8 compensation table. Most of the time there is a dip in the table at lower loads in the middle of the CTS range.

This dumps a bunch of heat into the exhaust and also warms up the engine faster.

RBob.

 

Beautiful, thank you! That makes the most sense since affecting commanded AFR would affect all other tables down the line.

So for example if we see a 10% value in the table and Stoich AFR was set to 14.7 in the BIN should we expect to command around a 13.27:1?

Do you mean Startup Enrichment? I haven't messed around with those at all yet.

Not a whole lot going on in that table currently. That chart I had to kind of find in the HAC. It starts at LC010F, but the HAC stops labeling addresses at LC10C just above it.

 

Yes, that would be -10%.

I had to look, yes, that is also called after-start fuel and also choke fueling. There is also after-start SA. Too many names for the same thing

Wow, that table has very little SA correction. Here is the same from AXKW, a $61 f-body TBI BIN (see pic). Note the highlighted area. Others I've seen are even more pronounced. Note that the KPa columns are vacuum, so 40 KPa vacuum is 60 KPa MAP if barometric is 100 KPa.

RBob.

 

Isn't that the truth! When I was building up that 32B XDF file I was constantly finding tables that were already in the XDF, but named slightly different than what was in the hac itself.


Wow... yeah very different than what I have here. My bin is based on ABTB and the HAC I used is ABTC which shows the same values as ABTB.

 

Rrob, did I catch the above point correctly, that to go richer I need to go minus not plus, or at least towards zero? You clearly indicated -10, not +10

I guess what I'm trying to figure out is if a I need a positive or negative number to get from lean to richer. Additionally, I've noted some tables some tables are decimals and entries less than 1.0 are permissible so that an entry could either will divide vs multiply results.

Had major restart issues today to the point of stalling out after seeing the AFR peg at 20.00 I believe I have been "trying " creating a larger positive value in my tables. I get the impression from you and the car, that maybe I'm going the wrong way.

I would believe there is a temp based modifier that I'm overlooking as well.

Part of this has been discussed as to change the metal MAT sensor over to the newer plastic sensor and move it forward into the incoming air stream rather than let it heat soak at the back of the plenum.

 

Great topic. Like scorp508 and lakeffect2 I’m also trying to get a grip on this concept, so please let me come at it another way. Looking at the stock 7730 $8D AUJP table for “Open Loop Fuel-Air Ratio %Change vs. Coolant Temp”, the values for 20* to 152*C are all 9.77. If stoich AFR is defined in the bin to be 14.73, does this mean that anytime the engine is in OL, and the temp is >= 20*C, the target AFR is calculated by the ECM to be 13.29 = 14.73 * (1 - .0977)? And then a second question. Would the 13.29 AFR be further influenced (enrichened) by the “Open Loop Fuel-Air Ratio %Change vs. MAP” table values since they are all positive? Again, stock AUJP 50 MAP value is 3.91. Does that mean the AFR is calculated to be 12.77 = 13.29 * (1 - .0391) at 50 MAP in OL? And further, if all that is true, how does the ECM actually use the revised AFR value in OL since all fueling in OL is coming from the VE Table.
Not trying to muddy the water -- just trying to understand how this all fits together.

 

Whether you enter a negative or positive value in the calibration editor is dependent upon how the person who created the definition file did it.

For the math see this link:

https://www.thirdgen.org/techbb2/sho...hreadid=214156

Even though it is for PE mode AFR, it is the same method for the open loop CTS modifier.

RBob.

 

RBob – With all due respect, you know more about this than I’ll probably ever know; but the less you say, the more I don’t understand and the more complicated it becomes. And, it’s not an issue of positive or negative numbers.
First, the link you provided does explain how AFR is used to calculate BPW. Thanks! Very informative. But that link strictly deals with WOT and introduces 2 more parameters that modify AFR that were not part of the discussion of this thread. Specifically (TunerPro titles):
Enrich Power Change AFR to RPM
Enrich Power Change AFR to Temp

Nowhere does Trax refer to the AFR parameters that are the subject of this thread:
Loop Open % Change AFR .vs. MAP
Loop Open % Change AFR .vs. Temp

So now I’m more confused. I understand what Trax is saying about WOT, but I remain as before not understanding the 2 parameters of this thread. Clearly there must be a difference between “Enrich Power Change AFR” and “Loop Open % Change AFR” and the purpose of these parameters and how they are used. An explanation of that would be greatly appreciated by anyone.

 

well ill try to help....

AFAIK, the %change v. MAP is an adjustment based on a more specific area in the load. experimenting with open loop idle in my car, this is a table i use to help fatten up or lean out a certain vacuum range. another member has a neat little spreadsheet to help calculate the final desired AFR.

%change v. coolant temp is an adjustment based on various coolant temps. say it runs stoich at 50*C but too rich throughout at 90*C, you can adjust this table to calculate desired AFR. using these tables with the VE tables should get you where you want to be. hopefully im not too far off lol, otherwise im starting over. HTH

http://ultm8z.com/DIY%20Tuning.htm

http://www.edgesz28.com/edgesz28/sup.../super8ecu.htm

 

The difference is one table defines the modifiers to base VE for Open Loop until your C/L criteria are met, the other table defines modifiers to be used by the ECM and applied to the base VE when you have met the Power Enrichment criteria. They work very similarly, but activated by differing conditions.

 

Thanks guys. What you both said makes perfect sense. Certainly did not intend to hijack this from you scorp508 and lakeffect2. Just have a lot of similar questions and the dots weren’t connecting but they’re now getting closer.

34blazer, were you successful in adjusting your OL idle rich/lean (ie – smell or plug read, as I don’t have wband) by merely changing the Loop Open % Change AFR .vs. MAP table, or did you also change AFR .vs. Temp and/or the VE table as well?

If this works, seems there is a possibility to lean OL idle since my bin has values of zero in the idle kpa fields. Can a negative number be entered to get a higher afr (leaner) since positive numbers elsewhere in the table are used to enrichen (7730, 8d, TPro super_8dm2.xdf)?

Thanks again!

 

the first time i adjusted both tables but i didnt realize that the afr v. temp table affected the whole temperature range. i actually ran too lean so i started over and just adjusted the afr v. map table. i tried using a negative but it wouldnt use it, just zeroed out. theres another scaler too, Loop Open Param, Idle, % Change AFR , that one was already at zero andf anything above that would richen the idle afr. its kinda funny, i lowered my values in the idle range on the ve table and it seemed to make little difference, then it started to surge when it got above 13.6:1. but when i enable closed loop, it will idle right around 14.7 with no surging.

*edit* this was before i raised my idle to 900rpms, since i have underdrive pulleys the voltage starts to drop off at 800 rpms. i have yet to try it at the new idle speed. once i get it running a little smoother i guess i have to start tweaking the injector offset v. voltage table. having design 3 bosch injectors doesnt help either since this table was probably designed for the pintle type injectors.

 

Well you've succeeded.


Feel free to start a new more targeted thread.

 

You can't use negatives in the VE table but you can increase the VE Bias or offset constant that will result in a negative VE.

 

Again, very sorry & will do. When lakeffect2 posted about rich/lean and the Loop Open % Change afr and there was further discussion about that, I thought I was on topic.

 

I took no offense, didn't see it as hijacked, only an honest attempt to learn. Can't tell you how many threads I've hijacked in the interest of understanding more on a subject. There's so much to learn, as you've asked questions I never even thought of. Good or bad, it's all knowledge. Learn from the bad.. apply the good.

I'm indebted well past my mortgage to guys like to JP, Traxion, and countless others (God bless Grumpy) for being kind enough to take me under their wings. Otherwise my TPI swap would have been a 4200lb lawn ornament.

My sincere thanks to all those who take time to share their knowledge.

Dave Buchholz, Rochester Ny

 

I was only ribbing you, no worries. I'd have a 40' nose if I tried to pretend I don't do the same.