Individual Cylinder Trims Discussion

I'd like to think I've searched the subject exhaustively, but if there's an in-depth write-up that I haven't found please feel free to flog me (after you point me in the right direction).

What I've found on the subject is mostly geared towards setups with tube headers - I'm thinking it's safe to assume no-one running log manifolds will be concerned with tuning this, but all discussion is welcome. From what I've read the drill is: measure exit temp with IR sensor, add fuel to the hotter holes assuming they're burning lean but don't discount the possibility of nearly dead cylinders reading cold from weak combustion (need more fuel). Rinse and repeat until you brick your ecm. :mad1:

A little background - my current (and probably only efi) project is a freshly rebuilt '95 LT1 with a fairly sloppy cam and headers. My understanding of the subject is that the individual cylinder trims are used to balance low-flow AFR to accommodate any cylinder to cylinder airflow differences.

So here are my observations, questions, discussion points, whatever.

1) Reading primary tube surface temps on headers in a car with the engine running seems a far cry from controlled experiment. Assuming you have a clean line of sight to some point on each tube, through experience I've observed reading different points at different distances from the flange or points around the primary bend produce vastly different results on the same cylinder.

2) eehack's cylinder balance test - disables one injector at a time and averages RPM and MAP changes to extrapolate relative cylinder strength. Obviously this is extremely platform specific, but can this be factored into the equation?

3) Is there any value in aiming for a summed balance between the banks - i.e. once a temperature balance is reached should one then strive to scale the right and left bank trim values so their sum is each roughly 4.00?

4) Short of fitting your heads / headers with individual EGT thermocouples, is there a better way? The IR thermometer seems a bit haphazard and my experiments with a single portable contact thermocouple have been problematic due to the amount of time needed to bring the sensor to equilibrium with the tube temperature.

I'm more than willing to find answers through trial and error, but if anyone would like to save my PCM a few dozen flash cycles your contributions will be greatly appreciated!

egt is tough. exhaust temp can be lower on leaner cylinders but if they're way rich, they will drop again, as the unburned fuel wont react and cools the pipe.. and as you noted heat transfer will screw over your results.

on race engines with individual throttle bodies, you just use vacuum per cylinder for balance. since you have shared vacuum in the manifold, the cylinder drop approach is a great method

of course perfect balance at idle isnt super critical, and as soon as you open the throttle plates, all hell breaks loose anyway.

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Originally Posted by steveo

egt is tough. exhaust temp can be lower on leaner cylinders but if they're way rich, they will drop again, as the unburned fuel wont react and cools the pipe.. and as you noted heat transfer will screw over your results.

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With all the accessory equipment on the odd bank I felt like I was herding cats trying to get reliable temps with the IR gun. It was even a "fancy" one with a laser aperture indicator.

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Originally Posted by steveo

since you have shared vacuum in the manifold, the cylinder drop approach is a great method

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The balance test showed that 1, 2 & 3 are overall the weakest, with 1 showing nearly 20% lower #s than the strongest holes (5 & 8). I know 1 & 2 are usually weaker on smallblocks with this type of intake plenum. But doesn't #1 also has the smallest idle air feed hole? I have to assume GMs engineers did this for a valid reason, but wonder if making them all the same size would do any good.

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Originally Posted by steveo

of course perfect balance at idle isnt super critical,

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I might have a touch of OCD so I take this statement as a challenge.

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Originally Posted by steveo

and as soon as you open the throttle plates, all hell breaks loose anyway.

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I know what you're saying, and I've read posts where you mention disabling the part-throttle individual trims. When I was running speed density to tune VE I noticed my cell 16 split was always lean on the even bank by +15-20, but the adjoining part-throttle cells (5,6,8 & 9) always had the odd bank showing lean. I was starting to wonder if I had accidentally plugged the post-cat O2 sensor into the primary connector.

Strangely, after I buttoned up my VE tuning and turned the MAF back on with no other changes to the tune the splits all but disappeared. Cell 16 split is averaging 1, and the worst tip-in cells (5 & 8) are 6. I'm starting to wonder if I can't use the part throttle cylinder trims to try and tweak this out. With a sloppy cam like this you can use every ounce of torque you can develop in those low airflow ranges.

Whatever the case, I'm baffled as to where the split "disappeared" to.

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Originally Posted by spfautsch

With all the accessory equipment on the odd bank I felt like I was herding cats trying to get reliable temps with the IR gun. It was even a "fancy" one with a laser aperture indicator.

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I've tried that several times. If i hold the gun upside down i can get upto 100Degrees C higher.

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The balance test showed that 1, 2 & 3 are overall the weakest, with 1 showing nearly 20% lower #s than the strongest holes (5 & 8). I know 1 & 2 are usually weaker on smallblocks with this type of intake plenum. But doesn't #1 also has the smallest idle air feed hole? I have to assume GMs engineers did this for a valid reason, but wonder if making them all the same size would do any good.
[/QUOTE}
The Balance test also seems to vary from day to day.
The front cylinders are set to have more fuel and the rear less in the cylinders in the stock tune.
Drilling the manifold idle hole out makes no difference at all as far as i've seen, although the drillings on the Edelbrock LT4 manifold is a bit crap to start with.
Splits move around & seem to come & go on a whim.
Idle timing changes, I have seen affect the timing on the injector BPW which i would expect to increase the BLM splits. As the timing increases the bpw drops but more on one side than the other.

[QOUTE]I might have a touch of OCD so I take this statement as a challenge.

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Me too. I want to know it's right.

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I know what you're saying, and I've read posts where you mention disabling the part-throttle individual trims. When I was running speed density to tune VE I noticed my cell 16 split was always lean on the even bank by +15-20, but the adjoining part-throttle cells (5,6,8 & 9) always had the odd bank showing lean. I was starting to wonder if I had accidentally plugged the post-cat O2 sensor into the primary connector.

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I suspect the Mac midlength headers for some of it.
The 02's seem to be sat in 1 pipe rather than reading an average in the collector so I think playing with the fueling doesn't really show up on the other 3 cylinders the same.

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Strangely, after I buttoned up my VE tuning and turned the MAF back on with no other changes to the tune the splits all but disappeared. Cell 16 split is averaging 1, and the worst tip-in cells (5 & 8) are 6. I'm starting to wonder if I can't use the part throttle cylinder trims to try and tweak this out. With a sloppy cam like this you can use every ounce of torque you can develop in those low airflow ranges.

Whatever the case, I'm baffled as to where the split "disappeared" to.

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Haven't got around to putting the MAF back in yet.
I went SD with some success but the wideband & narrowbands don't quite match up. Wideband ran really well but i felt was too rich.
The narrow bands feel a little light.
Since I've dropped the timing down loads again the car is much more relaxed than before.

If it's happy & it runs it will be fine.

HTH
Mitch

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Originally Posted by Terminal_Crazy

Haven't got around to putting the MAF back in yet.

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I've read a bunch about your project searching for ideas for mine - it may be worth the attempt. I was pretty frustrated with the parking lot manners in SD/CL but the difference is night and day with the MAF. I have no idea why, but I'm not going to look that gift horse in the mouth. I was on the fence as to whether it was worthwhile to finish installing the A/C piping and charge it, but I'm thinking it'll handle it now. :thumbsup:

The only issue I can't seem to resolve is surge / bucking in gear at closed throttle. I know the fix, but don't want to take idle timing out because at 29 the lope turns into a "dead cylinder" feel that shakes the car while at 30 you can barely feel it.

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Originally Posted by Terminal_Crazy

I suspect the Mac midlength headers for some of it.
The 02's seem to be sat in 1 pipe rather than reading an average in the collector so I think playing with the fueling doesn't really show up on the other 3 cylinders the same.

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What does your int delay table vs airflow, and corrcl vs airflow look like?

By my estimation the O2s are only around 6-8 inches further from the exhaust ports with mine (stainless works C4). I'm having trouble finding pics of your headers to compare.

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Originally Posted by spfautsch

I've read a bunch about your project searching for ideas for mine - it may be worth the attempt. I was pretty frustrated with the parking lot manners in SD/CL but the difference is night and day with the MAF. I have no idea why, but I'm not going to look that gift horse in the mouth. I was on the fence as to whether it was worthwhile to finish installing the A/C piping and charge it, but I'm thinking it'll handle it now. :thumbsup:

The only issue I can't seem to resolve is surge / bucking in gear at closed throttle. I know the fix, but don't want to take idle timing out because at 29 the lope turns into a "dead cylinder" feel that shakes the car while at 30 you can barely feel it.

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I might switch the MAF back of again then next time i go out.
Mine just felt uptight like itr was being held back.
Timing was around 39. Idle was really smooth but it didn't drive nice. SDOL fattened it up but it cruised nicely evreywhere else.
Increasing the timing smoothed idle, reduced Ibpw, reduced MAP etc etc everything we are looking for.... just drove a bit jerky.

I've since raised my O2 swing thresholds up. It passed the emmissions test like that and drives much better with the lowered timing.

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What does your int delay table vs airflow, and corrcl vs airflow look like?

By my estimation the O2s are only around 6-8 inches further from the exhaust ports with mine (stainless works C4). I'm having trouble finding pics of your headers to compare.

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[/QUOTE]
Fast 02 Rich/Lean
0 451
16 438
32 424
48 424
64 424

o2 Int Delay - Airflow
0 0.80
16 0.66
32 0.46
48 0.43
64 0.38

CorrCL - Airflow
0 08
16 26
32 26
48 26
64 32

I'll stick a pic of the headers on my website.
http://www.sand-hill.uk/TerminalCraz...Length_004.jpg

The port for the O2 sensor is basicaly at the end of the header pipe rather than in the collector.


Mitch

DISCLAIMER: I don't have the slightest clue as to what I'm doing, and have excessive amounts of what I hope is largely false knock. Nor do I have a wideband. So if you follow my advice you might need to have your head examined.

I did pull my plugs a few days ago and none show signs of detonation.

Your int delays seem excessive for such a short header.

I also found things stabilized somewhat when I took most of the "teeth" away from CORRCL.

This is what I'm currently running with the header below.

Code:

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INT DELAY vs AIRFLOW
725
212
150
125
112

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Code:

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CORRCL vs AIRFLOW
3.14
4.31
9.02
12.55
12.55

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Attachment 11750

As to your comment about feeling "held back", I have also noticed the throttle response isn't quite as crisp as it was when running SD. But if my splits never come back I'll deal with it.

having an integrator delay a bit on the long side doesn't really seem to hurt anything.

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As to your comment about feeling "held back", I have also noticed the throttle response isn't quite as crisp as it was when running SD. But if my splits never come back I'll deal with it.

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that's typical. the map sensor, tps, and everything else other than the maf responds damn near instantly. ve can tend to provide a natural accelerator pump effect, since vacuum often drops then recovers from quick throttle movements. the maf on the other hand, has a bit of a delay. i think it uses tps to try to account for it (i think kur4o was working on trying to tune that).

I want to argue with you on the integrator delays, but I'm obviously doing something wrong. The more logging I do in warm temps the more fuel it's taking out (BLMs dropping when ambient temps rise). I'm starting to think my false knock isn't all false. I also filled up tonight and calculated 21.9 mpg over the last two days. That seems highly improbable @ stoich with a cam with 50+ degrees of overlap.

I've already bumped the O2 swing voltages somewhat.

Code:

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00        525        525
16        525        525
32        459        459
48        459        459
64        459        459

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My guess is the slow nature of the MAF has helped reduce the splits by stabilizing the fueling calcs whereas in SD the MAP would fluctuate due to reversion at low airflows.

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I want to argue with you on the integrator delays, but I'm obviously doing something wrong.

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fuel is sprayed. o2 reads oxygen content. ECM responds by adding/subtracting fuel.

in this particular control system loop, you definitely need a decently sized delay, otherwise the change happens so quickly that you end up modulating.

the only side effect of being too long is that changes take longer to occur.

so what?

a few percent of fueling error never hurt anything.

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The more logging I do in warm temps the more fuel it's taking out (BLMs dropping when ambient temps rise)

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warmer air is less dense. humidity also plays a factor. warmer air requires less fuel. the IAT temperature compensation is imperfect. it's normal for trims to change during things like weather fluctuations.

don't get too OCD about keeping your trims perfect. let closed loop do SOME of the work. that's why it's there. otherwise just turn it off like i usually do

IMO........in reality, engines don't actually need or want a stoich mixture most of the time. i suggest you try driving while adding/subtracting a bunch 'o fuel so you get a feel for how much AFR actually affects an engine. staring at these blm numbers too long makes you lose sense of that. just because o2 sensors only read stoich doesn't mean your engine really cares how close you are to it, and a truly awesome tune definitely doesn't have to hover around stoich for most of its life.

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I've already bumped the O2 swing voltages somewhat.

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don't go too far. the o2 swing voltages should ideally be the actual switching @ stoich point of the sensors as seen by the ECM. the further you stray from that value the less stable things get.

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Originally Posted by steveo

in this particular control system loop, you definitely need a decently sized delay, otherwise the change happens so quickly that you end up modulating.

the only side effect of being too long is that changes take longer to occur.

so what?

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I suppose I was looking at the integrator delay purely from the standpoint of the engine as an air pump, and that we adjust it to compensate for the increased length of tube headers. Correct me if I'm wrong but isn't that only one (relatively insignificant) aspect of what we're accomplishing by increasing int delay?

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Originally Posted by steveo

a few percent of fueling error never hurt anything.

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I would have to revert back to SD to get a more exact #, but it looks like close to 15% over the past few days. I'm definitely running into what I would describe as debilitating lean spark knock in the afternoons in a load range that might only generate ten to twelve knock counts per hour in the morning. It was so bad yesterday afternoon I thought my one wheel bearing that I'd found to be sloppy had started growling. Then I looked down at datalog and noted KR pegged at 12 degrees and KC rolling like the wheels in a slot machine. IATs have been 82f with 70%rh in the AM and 108f with 50% in the PM.

I was thinking this was false knock from (roller rockers, headers, connecting rod clap, ???) because I use my cruise control a lot, and that causes the knock events to graph in a line on the RPM I'm cruising at. <planting face in palm>

Whatever the case, the int delay discussion caused me to think a bit about the closed loop parameters and how they're all using a derived airflow scalar from the reference table. I'm wondering what the program uses when the MAF is disabled / absent. Does it fall back to 00, and was it using my int delay and reference voltage from the 00 cells? That would certainly explain why switching my MAF back on has caused caused trims to shift. Was it Rob that disassembled EE?

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Originally Posted by steveo

the IAT temperature compensation is imperfect.

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How would IAT compensation figure into closed loop other than for base calculation? Don't the O2 sensors have the final say?

Edit: Further in that direction, isn't IAT pretty much irrelevant when using an air meter (MAF)?

One other thing I've been wondering, does anyone know how long the program samples the O2 sensors after the int delay timer has expired?

My understanding of how the closed loop metering works is that the sensor outputs a waveform somewhat similar to a sine, and the feedback routine read the peaks of the wave and divides by 2 to find the average?

Edit1: The idea I'm arriving at logically is that the engineers that wrote EE didn't intend the integrator delay to have anything to to with relative placement of the O2 sensors. My theory is it's used both as a delay to let the fueling changes settle in, and possibly also the oversampling window for reading the AD converter(s). But without disassembly notes or source code that's simply wild speculation. All I know is if I was building an opposed or crossplane cylinder engine controller with an arduino, that's how I'd do it - alternate between reading bank 1 while bank 2 is stabilizing and vice versa.

Edit2: Further thinking has reminded me that CORRCL is working in between integrator "cycles" so the program must be reading both O2s all the time.

Quote:

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Originally Posted by steveo

in this particular control system loop, you definitely need a decently sized delay, otherwise the change happens so quickly that you end up modulating.

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Would this be observable in any way? Fluctuating INT counts?

Tried raising O2 reference voltage in the cells I hadn't already and removing more from CORRCL, and the only place it seemed to add fuel was in cell 16.

Another thing I noticed is that somehow EGR was still coming on at low duty cycles even though I had the enable RPM well above the range it was coming in at, adding a degree of unwanted timing and further diluting the charge. I just zeroed the egr adder timing and set the enable RPM to 7000. Will try to log more before it cools off this evening.

The O2 doesn't output a sine wave and the algorithm doesn't just read the peaks and divide by 2. The output of the O2 is directly read and where it's voltage goes is a result of the control loop operating. Each time the O2 reverses direction it's because the control loop reverses the direction it's going with the fuel. In other words, the control loop adds fuel until the O2 swings to a high voltage and then it starts pulling fuel until the control loop swings to a lower voltage. A control loop is never perfectly stable. It always oscillates slightly around the desired setpoint.

If the integer acts too fast then it can pull fuel past the point where it should start adding fuel again. This happens because the O2's don't see the leaner fuel quick enough so they don't give feedback quick enough to tell the integer to "turn around" in time. So, a longer time makes the integer go slower and it is all more stable.

On a '7747 system, I observed a light throttle acceleration surging caused by the lean swing. I adjusted the O2 switch voltages slightly to stabilize that one.

Going back to your original intent. I can't see you having any sure-fire way to get the individual trims right unless you put 8 wideband O2 sensors on it. Possibly thermocouples could work too. IR sensing is way too sketchy.

I wish I could change the title of this thread as it's wandered off topic quite a bit. Whatever the case the 8 individual widebands is more or less the answer I was expecting. Thanks for the insight into the O2 feedback loop - it sounds very similar to how a PID servo feedback loop works.

The current state of the tune leads me to believe individual cylinder balance is not as big of a problem as I thought it might be. It may be when I drop the bigger injectors in however.

Since switching the MAF back on the idle has stabilized enough my wife could probably drive it without too much coaching (M6). This was the primary reason I was concerned with cylinder balance. When it was running SD it was so pathetically weak idling it needed nearly 1/4 throttle just to back into the driveway.

This afternoon I blended another degree of timing retard into the 1000-2000rpm x 30-70map range, and removed all EGR adder timing. Even though the EGR minimum enable RPM and MAP are both set well beyond reachable ranges, I am still seeing the EGR duty cycle toggling to 12.5% and back to 0 in cruising ranges so I have to assume that's where the unaccounted timing was coming from and hopefully the cause of the excessive KR at 1600rpm in 6th gear. I guess I need to pull the valve and solenoid and install a block off plate to be sure there's no exhaust (other than from valve overlap) finding its way into the intake charge. A short drive this afternoon hinted that zeroing the EGR spark adder table seemed to make the difference I was looking for, but I'll have to log more to be sure.

Quote:

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Originally Posted by steveo

warmer air is less dense. humidity also plays a factor. warmer air requires less fuel. the IAT temperature compensation is imperfect. it's normal for trims to change during things like weather fluctuations.

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I knew / know this happens and I've observed it, but I was a bit in freak out mode because it felt like it was running extremely lean and this is a new / replacement MAF sensor. I killed the 22 year old AC Delco cleaning it, and I had no reason to be overly confident the replacement would be identically calibrated.

I wish I'd noticed the EGR trying to enable sooner, it would have explained a lot. I assumed setting the enable RPM as high as possible and disable at 0 would kill it completely, but it still attempts to enable and adds spark before switching off.

Edit: I wonder if it would be worthwhile patching the EGR out completely, so as to save a few CPU cycles?

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Originally Posted by steveo

don't get too OCD about keeping your trims perfect. let closed loop do SOME of the work. that's why it's there. otherwise just turn it off like i usually do

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I do understand we're trying to re-shape the VE tables, not necessarily have BLMs at 128 everywhere. I guess the goal is to either log only in ideal conditions (still trying to determine what exactly that is) or have equal amounts of logging in extreme conditions and let the law of averages find the middle.

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Originally Posted by spfautsch

I wish I'd noticed the EGR trying to enable sooner, it would have explained a lot. I assumed setting the enable RPM as high as possible and disable at 0 would kill it completely, but it still attempts to enable and adds spark before switching off.

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could be a testing routine. 'vette calibrations have lots of extra tests to feed those pre-obdii pids. try disabling the egr error code and see if it goes away. with that cam an egr is kinda pointless, might as well just block it off, if for no other reason that it's ugly.

edit: often disabling the error code disables the test routine too. egr test involves popping the egr open for a moment during conditions when it's not usually operated, but it's unlikely the driver will notice and when vacuum is steady, and monitoring MAP for a slight drop in vacuum.

I just did that, hoping to flash and log tomorrow if the forecast pans out. Zeroing the spark adder along with smoothing out a degree of timing at the margins of this range seemed to make a big difference yesterday evening. It's very noticeable when you get into the hot air on the interstate. Am I ever glad I hadn't detuned knock retard.

Block off plate is ordered - I knew the cam would create boatloads of natural EGR but left the valve on for inspection b/c Missouri's rules want the emission devices to be there. They don't care if they're working but by the letter are supposed to be visible, so in emissions exempt counties like mine we have a lot of folks driving around with gutted cats that the inspectors can't say a thing about. It won't need inspection again until 2019, and after that I can register it as an antique vehicle so no inspections required.

Disabling the error code(s) didn't make any difference, the ALDL data shows the egr duty cycle toggling from 0 to 12.5% and back to 0 frame after frame. It's a weird quirk but I've disconnected the solenoid so it's no matter.

Didn't resolve my issue anyway.

I think it might be a high pitched exhaust droning / resonance I've been hearing for a while, seems to only do it when the exhaust is hot. I noticed it this morning with the windows down at a low enough speed, and happened to be looking at the knock count at the time. Very odd, almost sounds like if you were to let the air out of a balloon while stretching the neck so it squeals. I didn't notice it at all when I made a short log yesterday (with fairly low knock counts) but my wife was with me so the suspension and chassis could have been settled differently.

After finding a "smoking gun" cracked exhaust tip that was surely the cause of the goose-pitched exhaust drone and welding it up I'm sad to say not much has changed. I'm going to move my (false?) knock issue to a new thread so as not to steer this thread even further off the title.

I did however want to report that on a whim I added some individual trim to #1 as it was reporting weakest on the eehack cylinder balance test, with decent results.

Quote:

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Originally Posted by steveo

since you have shared vacuum in the manifold, the cylinder drop approach is a great method

of course perfect balance at idle isnt super critical, and as soon as you open the throttle plates, all hell breaks loose anyway.

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My thinking was that a possibly leaner cylinder was exacerbating a possible lean swing condition in cruising cells, causing knock. I haven't completely ruled out this possibility, but I did greatly lower the individual trims tps limit so it shouldn't be an issue in any realized load range.

Beyond that, my main concern with cylinder balance is how individual trims might affect cell 16 and any BLM split there. I've completely revised my timing tables, so most of my logging data in regards to that has become more or less invalid. However, I'd love to hear thoughts on the value of making the sum of the indvidual trim banks add up to something close to 4 and 4.

Whatever the case, if the worst idle split I see is 4-6 counts as observed yesterday I'll have no problem calling that "good enough".