DIY LTCC or similar system for LT1s

[spfautsch]

... that capacitor is not between controller and resistor{AS per PCM design}, but is between resistor and coil. Do you think it will make any difference.

Without knowing the type of outputs the ICs in the PCM use along with the size of the caps it's hard to know what they were trying to accomplish there. Am I correct to assume that is an ASIC (i.e. made to order for a specific application)? Whatever the case, this is why I asked for testers, not customers wanting to buy a turn-key complete product, which this is not. With that said, I haven't noticed any controller resets while running with this RC network configuration so I'm working on the assumption they're doing their job adequately.

Also the temp compensation is tied with voltage, so in the end there is 3d matrix of adjustments. If it was so unimportant I doubt GM will make an effort to dial those tables.

I left this at "I'm going to look into the possibility" (of adding temperature compensation). No idea where you're getting the idea that I don't think it's important. I just don't think it makes sense to blindly emulate the factory tables when there are so many variables (most notably coil mounting location). For example, though I'm only vaguely familiar with the LS1/2/3/6 engines, weren't all the coil packs mounted directly on the (aluminum) valve covers? Didn't they also mostly have "dress-up" covers? All this can and does affect coil operating temperature. The coil mounting options on gen 2 LT-1s are much different and can be a matter of personal choice. All these variables need to be taken into consideration. To be thorough about it, one would have to mount temperature sensors on the coil packs and run the vehicle. I don't quite have the time or the R&D budget to accomplish that, much less willing test candidates. Which is why I've somewhat left the project at the "it's working for me" state. Though I'd like to, this is one of the primary reasons why I'm not trying to make money with it - the money I've taken in hasn't scratched the surface of my costs for the materials, not to mention the time spent ordering, counting out the parts, packaging, defective out-of-the-package AVRs, etc.

I am not a fan of `kind of worked` approach or it will work only at room temperature approach. It either gets done the right way or goes underground.

Then perhaps this isn't something you would want to participate in. I hope you've read the comment header previously, but if not, and to make it clear for readers new to the thread.

From the source .ino file (it's written in c++):

////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//
//  this code is to be considered experimental and is provided "as is", without warranty of any kind,
//  expressed or implied, including but not limited to fitness for a particular purpose.
//  if your LT1 comes apart using it i will not be held responsible
//  you were warned

Now I need a firmware for SPFcop

The name of the project was taken from the title of this thread. It's silk-screened on the PCB. It's quite certainly not "SPFcop". I just don't want you referring to it as LTCC which is Bob Bailey's product. Both for copyright concerns, and to prevent readers from being confused as to what we're talking about. Over the last year or so I've simply been calling it "the controller" because it's the subject of the thread.

... that runs dual mode based on rpm threshold. All the time it will calculate dwell as needed but on lower rpms based on threshold it will run as sequencer. I think it will be a piece of cake to add sequencer mode with a rpm switch on top of the existing code.

Since (I assume) it would require a patch for the PCM, I would consider that a possible option for startup dwell if, and only if temperature compensation within the controller is not feasible. I won't be able to investigate that for at least a couple weeks, best case.

I'm really hoping to have time this weekend to get some preliminary test data on the coils across a reasonable temperature spectrum. I have a cheapo toaster oven and a nice industrial process heater controller ready to be combined into a semi-lab worthy piece of equipment.

Too bad you have a manual and can`t test a downshift.

This is a typical downshift into my favorite hard left corner. It's nowhere near as abrupt as an automatic, but I think you'll find the overrun clutch hub in the 4l60e will only handle a limited amount of abuse like that before it fractures.



Next time I have a chance and traffic allows it I'll try a downshift to 2nd which should get the revs a lot higher. Whatever the case I'm not going to let the chassis do all the work because going from 5th to 2nd without rev matching will certainly break the tires loose, not to mention beating the hell out of the driveline.

Edit: It occurred to me after re-reading this that you were talking about a throttle kickdown type downshift. This is the kind of thing that makes me cringe because I know it's really hard on the trans, and rebuilding autos is a messy pain in the backside.

[kur4o]

Kickdowns are violent as hell, especially on 2-1 downshift. I think WOT upshifts are much more harder on the trans, newer PCM reduce engine power on that conditions.

Using the stock coolant sensor signal is real PIA. It is a 5volt pulled down by the resistance of the sensor. It is also unlinear output. There is 256 byte table lookup in the pcm to cover the unlinear conversion. I don`t know if it is good idea to sense the pin output straight without interference. The best approach is external temp probe on a coil to measure the temp.
Don`t forget to test subzero temperatures also.

I run some more tests today, changing dwell realtime on an idle running vehicle. Lowering it down to 1.3ms I could feel hesitation. Around 2ms the engine run fine. I tried different dwell on higher rpms but couldn`t tell any difference from 2 to 5 ms. I guess it will matter when the engine is loaded on higher gear. I will have to make some pulls to confirm it. Since the ignition is wasted spark, each coil fires twice and the off time on higher rpm is really small. So the stress I put on the coil is enormous.

`the controller` is some too general. It is time to find a new name for the project. SPFautch CoilOnPlug doesn`t seem good enough.

I am in need for a new coil set, and some good weather too so , I wont be able to test the controller any time soon.
I think it is time to measure the coil output energy. I need this to decide which coils to get. I still think that by chance you got the most appropriate coils for this project. The newer style round ones. They have the least dwell times and the best temperature stability. Now it is time to tell how much energy they output compared to other ones.

[spfautsch]

Using the stock coolant sensor signal is real PIA ... There is 256 byte table lookup in the pcm to cover the unlinear conversion.

I'm glad you mentioned that, because that's going to be my approach. So does this mean the ECT byte in the datastream isn't the raw ADC value but converted / conditioned?

Do you recall the address of that table offhand?

The best approach is external temp probe on a coil to measure the temp.

True, but somewhat impractical.

Don`t forget to test subzero temperatures also.

Already on my todo list.

... the ignition is wasted spark, each coil fires twice and the off time on higher rpm is really small.

Waste spark explains your 100x better comment. You're comparing apples to oranges.

`the controller` is some too general. It is time to find a new name for the project. SPFautch CoilOnPlug doesn`t seem good enough.

I just had 75 PCBs made with 'diy-ltcc rev 1.1' printed on them. The name of the project isn't open for debate unless you want to create your own fork.

I still think that by chance you got the most appropriate coils for this project.

You're absolutely correct there.

Now it is time to tell how much energy they output compared to other ones.

Unfortunately I haven't devised a way to measure secondary voltage, so have no reasonable method to do this at the current time. But I can tell you from the sound of the spark in free air that the D585 coils are beasts. I highly doubt the 8183 or D514a coils come close in maximum energy. But as I've mentioned they also have the massive detractor of hard / absolute dwell limiting.

Edit: I forgot to mention that after some preliminary voltage sweep tests (17-12 volts) with all the coils a few nights ago it became apparent the 8183 coils do indeed have some type of internal step-up power supply. The added noise created by the 300kz variable regulator amplified the noise on the charge current waveform immensely, making it really difficult to see the dwell limiting "knee".

Edit #2: Here's a pic of the new board next to the v1.0 board. No major changes save the addition of a few IDC headers. I have 18 complete parts kits available and another 55 bare boards.

[kur4o]

Here is the temp conversion. The signal is also inverted so rawAD $00 equals $FF scaled
The scaled output is converted to temp as follow.
$00=-40
$10=-28
$20=-16
$30=-4
$40=8
$50=20
$60=32
$70=44
$80=56
$90=68
$A0=80
$B0=92
$C0=104
$D0=116
$E0=128
$F0=140
$FF=151

                                       SCALED                                                   RAW AD
RESERVED:7FEE                 fcb $FF                 ; raw coolant cal table     $00
RESERVED:7FEF                 fcb $FF                                                    $01
RESERVED:7FF0                 fcb $FF                                                    $02
RESERVED:7FF1                 fcb $FE ; ¦
RESERVED:7FF2                 fcb $ED ; ý
RESERVED:7FF3                 fcb $E1 ; ñ
RESERVED:7FF4                 fcb $D7 ; +
RESERVED:7FF5                 fcb $CF ; ¦
RESERVED:7FF6                 fcb $C9 ; ã
RESERVED:7FF7                 fcb $C3 ; +
RESERVED:7FF8                 fcb $BE ; -
RESERVED:7FF9                 fcb $B9 ; ¦
RESERVED:7FFA                 fcb $B5 ; ¦
RESERVED:7FFB                 fcb $B2 ; -
RESERVED:7FFC                 fcb $AE ; î
RESERVED:7FFD                 fcb $AB ; ë
RESERVED:7FFE                 fcb $A8 ; è
RESERVED:7FFF                 fcb $A6 ; æ
RESERVED:8000                 fcb $A3 ; ã
RESERVED:8001                 fcb $A1 ; á
RESERVED:8002                 fcb $9F ; ß
RESERVED:8003                 fcb $9D ; Ý
RESERVED:8004                 fcb $9B ; Û
RESERVED:8005                 fcb $99 ; Ù
RESERVED:8006                 fcb $97 ; ×
RESERVED:8007                 fcb $95 ; Õ
RESERVED:8008                 fcb $93 ; Ó
RESERVED:8009                 fcb $92 ; Ò
RESERVED:800A                 fcb $90 ; Ð
RESERVED:800B                 fcb $8F ; Ï
RESERVED:800C                 fcb $8D ; Í
RESERVED:800D                 fcb $8C ; Ì
RESERVED:800E                 fcb $8B ; Ë
RESERVED:800F                 fcb $89 ; É
RESERVED:8010                 fcb $88 ; È
RESERVED:8011                 fcb $87 ; Ç
RESERVED:8012                 fcb $86 ; Æ
RESERVED:8013                 fcb $85 ; Å
RESERVED:8014                 fcb $83 ; Ã
RESERVED:8015                 fcb $82 ; Â
RESERVED:8016                 fcb $81 ; Á
RESERVED:8017                 fcb $80 ; À
RESERVED:8018                 fcb $7F ; 
RESERVED:8019                 fcb $7E ; ~
RESERVED:801A                 fcb $7D ; }
RESERVED:801B                 fcb $7C ; |
RESERVED:801C                 fcb $7C ; |
RESERVED:801D                 fcb $7B ; {
RESERVED:801E                 fcb $7A ; z
RESERVED:801F                 fcb $79 ; y
RESERVED:8020                 fcb $78 ; x
RESERVED:8021                 fcb $77 ; w
RESERVED:8022                 fcb $76 ; v
RESERVED:8023                 fcb $76 ; v
RESERVED:8024                 fcb $75 ; u
RESERVED:8025                 fcb $74 ; t
RESERVED:8026                 fcb $73 ; s
RESERVED:8027                 fcb $72 ; r
RESERVED:8028                 fcb $72 ; r
RESERVED:8029                 fcb $71 ; q
RESERVED:802A                 fcb $70 ; p
RESERVED:802B                 fcb $70 ; p
RESERVED:802C                 fcb $6F ; o
RESERVED:802D                 fcb $6E ; n
RESERVED:802E                 fcb $6E ; n
RESERVED:802F                 fcb $6D ; m
RESERVED:8030                 fcb $6C ; l
RESERVED:8031                 fcb $6C ; l
RESERVED:8032                 fcb $6B ; k
RESERVED:8033                 fcb $6A ; j
RESERVED:8034                 fcb $6A ; j
RESERVED:8035                 fcb $69 ; i
RESERVED:8036                 fcb $68 ; h
RESERVED:8037                 fcb $68 ; h
RESERVED:8038                 fcb $67 ; g
RESERVED:8039                 fcb $67 ; g
RESERVED:803A                 fcb $66 ; f
RESERVED:803B                 fcb $65 ; e
RESERVED:803C                 fcb $65 ; e
RESERVED:803D                 fcb $64 ; d
RESERVED:803E                 fcb $64 ; d
RESERVED:803F                 fcb $63 ; c
RESERVED:8040                 fcb $63 ; c
RESERVED:8041                 fcb $62 ; b
RESERVED:8042                 fcb $62 ; b
RESERVED:8043                 fcb $61 ; a
RESERVED:8044                 fcb $60 ; `
RESERVED:8045                 fcb $60 ; `
RESERVED:8046                 fcb $5F ; _
RESERVED:8047                 fcb $5F ; _
RESERVED:8048                 fcb $5E ; ^
RESERVED:8049                 fcb $5E ; ^
RESERVED:804A                 fcb $5D ; ]
RESERVED:804B                 fcb $5D ; ]
RESERVED:804C                 fcb $5C ; \
RESERVED:804D                 fcb $5C ; \
RESERVED:804E                 fcb $5B ; [
RESERVED:804F                 fcb $5B ; [
RESERVED:8050                 fcb $5A ; Z
RESERVED:8051                 fcb $5A ; Z
RESERVED:8052                 fcb $59 ; Y
RESERVED:8053                 fcb $59 ; Y
RESERVED:8054                 fcb $58 ; X
RESERVED:8055                 fcb $58 ; X
RESERVED:8056                 fcb $57 ; W
RESERVED:8057                 fcb $57 ; W
RESERVED:8058                 fcb $56 ; V
RESERVED:8059                 fcb $56 ; V
RESERVED:805A                 fcb $56 ; V
RESERVED:805B                 fcb $55 ; U
RESERVED:805C                 fcb $55 ; U
RESERVED:805D                 fcb $54 ; T
RESERVED:805E                 fcb $54 ; T
RESERVED:805F                 fcb $53 ; S
RESERVED:8060                 fcb $53 ; S
RESERVED:8061                 fcb $52 ; R
RESERVED:8062                 fcb $52 ; R
RESERVED:8063                 fcb $51 ; Q
RESERVED:8064                 fcb $51 ; Q
RESERVED:8065                 fcb $50 ; P
RESERVED:8066                 fcb $50 ; P
RESERVED:8067                 fcb $50 ; P
RESERVED:8068                 fcb $4F ; O
RESERVED:8069                 fcb $4F ; O
RESERVED:806A                 fcb $4E ; N
RESERVED:806B                 fcb $4E ; N
RESERVED:806C                 fcb $4D ; M
RESERVED:806D                 fcb $4D ; M
RESERVED:806E                 fcb $4D ; M
RESERVED:806F                 fcb $4C ; L
RESERVED:8070                 fcb $4C ; L
RESERVED:8071                 fcb $4B ; K
RESERVED:8072                 fcb $4B ; K
RESERVED:8073                 fcb $4A ; J
RESERVED:8074                 fcb $4A ; J
RESERVED:8075                 fcb $49 ; I
RESERVED:8076                 fcb $49 ; I
RESERVED:8077                 fcb $49 ; I
RESERVED:8078                 fcb $48 ; H
RESERVED:8079                 fcb $48 ; H
RESERVED:807A                 fcb $47 ; G
RESERVED:807B                 fcb $47 ; G
RESERVED:807C                 fcb $46 ; F
RESERVED:807D                 fcb $46 ; F
RESERVED:807E                 fcb $46 ; F
RESERVED:807F                 fcb $45 ; E
RESERVED:8080                 fcb $45 ; E
RESERVED:8081                 fcb $44 ; D
RESERVED:8082                 fcb $44 ; D
RESERVED:8083                 fcb $43 ; C
RESERVED:8084                 fcb $43 ; C
RESERVED:8085                 fcb $43 ; C
RESERVED:8086                 fcb $42 ; B
RESERVED:8087                 fcb $42 ; B
RESERVED:8088                 fcb $41 ; A
RESERVED:8089                 fcb $41 ; A
RESERVED:808A                 fcb $40 ; @
RESERVED:808B                 fcb $40 ; @
RESERVED:808C                 fcb $3F ; ?
RESERVED:808D                 fcb $3F ; ?
RESERVED:808E                 fcb $3F ; ?
RESERVED:808F                 fcb $3E ; >
RESERVED:8090                 fcb $3E ; >
RESERVED:8091                 fcb $3D ; =
RESERVED:8092                 fcb $3D ; =
RESERVED:8093                 fcb $3C ; <
RESERVED:8094                 fcb $3C ; <
RESERVED:8095                 fcb $3B ; ;
RESERVED:8096                 fcb $3B ; ;
RESERVED:8097                 fcb $3B ; ;
RESERVED:8098                 fcb $3A ; :
RESERVED:8099                 fcb $3A ; :
RESERVED:809A                 fcb $39 ; 9
RESERVED:809B                 fcb $39 ; 9
RESERVED:809C                 fcb $38 ; 8
RESERVED:809D                 fcb $38 ; 8
RESERVED:809E                 fcb $37 ; 7
RESERVED:809F                 fcb $37 ; 7
RESERVED:80A0                 fcb $36 ; 6
RESERVED:80A1                 fcb $36 ; 6
RESERVED:80A2                 fcb $36 ; 6
RESERVED:80A3                 fcb $35 ; 5
RESERVED:80A4                 fcb $35 ; 5
RESERVED:80A5                 fcb $34 ; 4
RESERVED:80A6                 fcb $34 ; 4
RESERVED:80A7                 fcb $33 ; 3
RESERVED:80A8                 fcb $33 ; 3
RESERVED:80A9                 fcb $32 ; 2
RESERVED:80AA                 fcb $32 ; 2
RESERVED:80AB                 fcb $31 ; 1
RESERVED:80AC                 fcb $31 ; 1
RESERVED:80AD                 fcb $30 ; 0
RESERVED:80AE                 fcb $30 ; 0
RESERVED:80AF                 fcb $2F ; /
RESERVED:80B0                 fcb $2F ; /
RESERVED:80B1                 fcb $2E ; .
RESERVED:80B2                 fcb $2D ; -
RESERVED:80B3                 fcb $2D ; -
RESERVED:80B4                 fcb $2C ; ,
RESERVED:80B5                 fcb $2C ; ,
RESERVED:80B6                 fcb $2B ; +
RESERVED:80B7                 fcb $2B ; +
RESERVED:80B8                 fcb $2A ; *
RESERVED:80B9                 fcb $2A ; *
RESERVED:80BA                 fcb $29 ; )
RESERVED:80BB                 fcb $28 ; (
RESERVED:80BC                 fcb $28 ; (
RESERVED:80BD                 fcb $27 ; '
RESERVED:80BE                 fcb $27 ; '
RESERVED:80BF                 fcb $26 ; &
RESERVED:80C0                 fcb $25 ; %
RESERVED:80C1                 fcb $25 ; %
RESERVED:80C2                 fcb $24 ; $
RESERVED:80C3                 fcb $23 ; #
RESERVED:80C4                 fcb $23 ; #
RESERVED:80C5                 fcb $22 ; "
RESERVED:80C6                 fcb $21 ; !
RESERVED:80C7                 fcb $21 ; !
RESERVED:80C8                 fcb $20
RESERVED:80C9                 fcb $1F
RESERVED:80CA                 fcb $1F
RESERVED:80CB                 fcb $1E
RESERVED:80CC                 fcb $1D
RESERVED:80CD                 fcb $1C
RESERVED:80CE                 fcb $1C
RESERVED:80CF                 fcb $1B
RESERVED:80D0                 fcb $1A
RESERVED:80D1                 fcb $19
RESERVED:80D2                 fcb $18
RESERVED:80D3                 fcb $17
RESERVED:80D4                 fcb $16
RESERVED:80D5                 fcb $15
RESERVED:80D6                 fcb $14
RESERVED:80D7                 fcb $13
RESERVED:80D8                 fcb $12
RESERVED:80D9                 fcb $11
RESERVED:80DA                 fcb $10
RESERVED:80DB                 fcb  $F
RESERVED:80DC                 fcb  $D
RESERVED:80DD                 fcb  $C
RESERVED:80DE                 fcb  $B
RESERVED:80DF                 fcb   9
RESERVED:80E0                 fcb   8
RESERVED:80E1                 fcb   6
RESERVED:80E2                 fcb   4
RESERVED:80E3                 fcb   3
RESERVED:80E4                 fcb   1
RESERVED:80E5                 fcb   0
RESERVED:80E6                 fcb   0
RESERVED:80E7                 fcb   0
RESERVED:80E8                 fcb   0
RESERVED:80E9                 fcb   0
RESERVED:80EA                 fcb   0
RESERVED:80EB                 fcb   0
RESERVED:80EC                 fcb   0                                   $FE
RESERVED:80ED                 fcb   0                                   $FF

it became apparent the 8183 coils do indeed have some type of internal step-up power supply.

That can explain the shorter dwell time of the coils. If the charge voltage is increased internally to 18-20 volts, the charge time will decrease immensly. I read somewhere that the newer coils didn`t draw that much current and the output voltage was like 30kv, compared to 50kv on earlier coils.

Is there any way to measure discharge time of the coil. I did make some calculation how that multispark might work.
At 800 rpm and 20 degrees spark advance, the time from spark event and TDC will be around 4.44 ms, If discharge time is fast enough, like 0.5 ms you can charge the coil again for 1-2ms and fire again at around TDC.

It might be designed for that kind of system but never fully implemented. Do you think the avr might be capable for some multispark tests at low rpms?

[spfautsch]

Thanks for the adc info on the coolant temp sensor. As long as there's nothing squirrely going on with the way the voltage divider circuit in the ecu is setup, I don't anticipate there will be a problem. Of course, if it works there's still a need for a bias multiplier to adjust for coil mounting location, etc.

I've been playing with my "easy bake" oven most of the day today, and I'm learning which is always good!



I do loves me the smell of freshly baked ignition coils!

That can explain the shorter dwell time of the coils. If the charge voltage is increased internally ... I read somewhere that the newer coils didn`t draw that much current and the output voltage was like 30kv, compared to 50kv on earlier coils.

This seems to be confirmation these are actual capacitive discharge designs. With that said, I accidentally zapped myself with one of these today and though it's a completely anecdotal "measurement", it didn't bite near as hard as the D585 coil.

Disclaimer: I do not recommend this method for "measuring" spark energy. Always lick the palm of your hand first!

Is there any way to measure discharge time of the coil.

Discharge time is pretty sketchy with this setup. My scope is almost as old as I am, and using a current tap on the spark plug results in very hard to sync signals that go from a moderately identifiable spike, to jumping way off the scale - (i.e. it's hard to get a stable waveform).

Do you think the avr might be capable for some multispark tests at low rpms?

That would depend highly on discharge time, but it's certainly a possibility, even at moderate cruise speeds with lots of spark advance. But there's a lot of distance between where we're at currently, and having a perfectly dialed-in dwell table that allows for multiple spark discharges.

What I'm finding after going through the 70c temperature range, and most of the 90c range is that below 12 volts the dwell limiting of the coils seem to change somewhat (it's more observable with the D580, D581 and 8183). Because of this I think I really need to build a zener diode stack to get a more accurate picture of spark energy so I can come up with a reasonable dwell number where spark energy stops increasing. It seems like below 10-11 volts you can dwell the coils as long as you want without a clear "knee" in the primary current (signifying the onset of dwell limiting).

I'm going to continue to test for dwell limiting across at least one or two more temperature bands, but I think to get meaningful data I'll need to measure spark energy (which is a good thing).

[kur4o]

I do loves me the smell of freshly baked ignition coils!

Nice you should try to make a coil cake special for tuning maniacs. I would love to taste it.

It seems like below 10-11 volts you can dwell the coils as long as you want without a clear "knee" in the primary current

It might be because the dwell limiter circuit didn`t get kicked in by a specified threshold of something. Still the excessive dwell will cause heat to build up and melt the coil. Energy is never lost, it is transferred to something else.

[spfautsch]

It might be because the dwell limiter circuit didn`t get kicked in by a specified threshold of something. Still the excessive dwell will cause heat to build up and melt the coil. Energy is never lost, it is transferred to something else.

I haven't broken out my slide rule to calculate potential energy, but I suspect that below 12 volts the "creators" knew the engine was either cranking, or wouldn't be running much longer, and that the longer it ran the less energy there would be to dissipate (because the alternator was dead) so no point enforcing dwell limiting. But that's just a guess. The last car I drove until it died because of a dead alternator was a '78 Malibu with a HEI-1 distributor setup. I can still feel my mullet tickling the part of my back the wife-beater left exposed - oh, to have hair again...

Edit: I did a bit of tweaking on the scope and managed to get what I feel is a reasonable idea of spark duration. When I get a chance to work through the videos I've made I'm hoping to get a picture or two of the waveform to explain better, but my measurements were from the rising edge of the spark current to the point where it crossed zero. After crossing zero there's a significant amount of oscillation that goes on for around 1ms. When I finish getting all the dwell limits I'll play around with a multiple discharge configuration because it seems like there may be enough time. Anyway, this is what I'm seeing (this data was gathered at 60c). Interestingly, the laminated steel core coils demonstrated much longer spark. I have to assume the barrel shaped coils have some sort of ferrite composite core.

D580 @ 12-14 volts, 5.6-4.2ms, 2.4ms spark time, 1.5ms oscillation
D581 @ 12-14 volts, 5.8-4.4ms, 2.65ms spark time, 0.6ms oscillation
D514a @ 12-14 volts, 7.8-5.25ms, 2.0ms spark time, 0.35ms oscillation
8183 @ 12-14 volts, 4.4-3.4ms, 2.0ms spark time, 0.35ms oscillation
D585 @ 12-14 volts, 7.8-4.45ms, 1.8ms spark time, 0.55ms oscillation

[spfautsch]

I wanted to drop in with an update since it's been a while. I've been making progress with coil testing, but the past week has been far less productive than I had hoped due to jury duty and my ISP needing to make it clear I'm at their mercy when it comes to having internet access.

Anyway, aside from the clothes dryer popping a thermal fuse due to the unusually cold temps, today was very productive. Mother nature graced me with a frigidly cold day that allowed the testing of a huge range of temps that would have otherwise been a major ordeal without being able to drop the "lab oven" out on my back deck in -14c ambients.

Here's what I've learned.

As I've mentioned in a previous post, I'm seeing a pattern where dwell limiting seems to "switch off" at a certain voltage. After additional testing I'm finding this pattern is also temperature dependent, and is different with each coil. In hindsight, this explains why I spent a lot of time testing at temps > 40c looking for the primary current knee at lower voltages when there was nothing to observe.

At lower temperatures most of the coils demonstrate a slight "trough" around 10-20c where dwell limiting is slightly reduced.

The act of measuring dwell limiting affects internal coil temperature, which changes the results. Because of this I've discovered it's most efficient to measure only a few voltage points per temperature band, and then return the coil to the controlled temperature environment to "re-normalize" while testing another coil.

Here's what I'd like to learn.

In a couple words, spark energy. Even though I can get a relative waveform to compare each coil's secondary current, I've found when firing into an air gap (aka, spark plug) the current jumps way off the scale on my scope regardless of the voltage divider I'm using to scale the transformer output. I feel like building a zener diode pile will be necessary to get this current down to a consistently quantifiable magnitude.

Additionally, measuring secondary (i.e. spark) voltage would be meaningful because there can be significant variations in secondary voltage based on winding ratios.

Lastly, primary current. I'd like to have a real-world current number associated with each coil based on it's thirst for DC current, but my home-made current transformer didn't come with a datasheet. Eventually I might break down and buy a commercial, calibrated current probe. But I'm also not too proud to borrow one if anyone's willing to lend one.

Another question that I continue to find myself asking is are there any other coils out there that we'd benefit from having data on? I'm not terribly excited to spend my own money on more test subjects, but if there's another part # I don't currently know about, by definition I can't and therefor won't spend the time to discover it. That's on you guys, but I very well might buy one to test if I had a part #.

So, that's where things are at. If this coming week is as slow as I was hoping last week would've been, I hope to have a preliminary "report" to post soon.

[In-Tech]

Some things my bud Dave shared with me, also a snip of what GM is doing. I used to work for Mallory Ignition and I have been friends with Dave Telling for a long time.

[In-Tech]

Also you really want to think about a pressure chamber to test spark. Here's a couple pics of mine. And where distributor machines go to die

[spfautsch]

Interesting reading material - thanks for sharing!

For what we're trying to accomplish here a pressure chamber is probably overkill. But the zener pile schematic is greatly appreciated. I'd never considered the benefit of creating a bi-directional stack to allow for whatever polarity the discharge is delivered at.

[In-Tech]

I thought you all might like that diode "bridge", it sure helps the o-scope stuff :) Carry on, I'm just listening but will help what I can whenever I can and Dave is just a phone call away when I get lost on stuff.
-Carl

[vilefly]

I'll refer you to page 20, post #288. But this one should be of primary interest to you guys.
ion-sense-ignition.png

Note the stacking of the diodes. 5 diodes @1v voltage drop each = 5V signal. The very noisy power supply (timing light) I used at the time was an issue, but the primary and ion sense currents were accounted for in my oscilloscope waveform. To be honest, I didn't think it would work, but it did. The rectifier diodes were rated for 1kv or so. The voltage differential acted like 5 little batteries that "charged" with current demand. I'm sure I forgot the dynamics of the circuit (it was 15yrs ago), but it could hold some potential to be adapted. Looks like I need to get back on the ball with my ion sense ignition ideas before you guys pass me up.
You had me lost in the programming tech talk, but I hope to contribute more.

[vilefly]

On second thought, it looks like this probably would not be adaptable for a 13.5V system. You would have to run 18.5V to compensate for the voltage drop, and would need 10-15A diodes to get enough current through. I still have plans for it, though. A wire shunt instead of diodes would work, though.

To find out spark energy, an inductance reading would be required, but the coils' built-in circuitry defies taking accurate readings. Perhaps reading from the positive lead to the secondary lead might lend a clue, but I can't be too sure about it.

[spfautsch]

Here's the data I have thus far. Note that I only measured spark duration for a few cells. This isn't nearly as complete a of picture of the data that I set out to gather initially, but it's what I have now. As I've mentioned I'd really like to build a zener pile to allow accurate measurement of spark energy, but I'm starting to lose my ambition after discovering how time consuming the process has been thus far.

Dwell Time to Limiting vs Temp vs Voltage.xlsx

Zip of spreadsheet, arduino test sketch and waveform images (9mb)

Apologies for the shoddy waveform images and camera work, but I really don't have the time or interest to try doctoring them up to remove glare, my reflection, etc.

I would like to get a test at -20c but I'm at the mercy of mother nature on that for the time being. If I can find a decent thermometer I can try using a freezer, but I'm not feeling as motivated to get a thorough picture of this information at the present time.

My methodology was to allow the coils to normalize thermally for ~30 minutes, then test at approximately four voltages before returning to the temperature controlled environment for another 10 minutes while another coil was being tested. System voltage was difficult to set exactly, but I made every effort to get within 10mv of the target value. I generally started at 8.00v and worked upwards until I discovered the pattern developing that I'll describe in the next section. Running at a 50ms loop time, dwell was gradually increased until a clear indication of internal dwell limiting was exhibited on the primary current waveform, and then reduced only as much as was necessary to remove said indication. At this point the test sketch was stopped from the serial console, system voltage was adjusted to the next target value, and the process repeated until a temperature range was complete. Then another ~30 minute normalization period was allowed to pass, rinse and repeat.

To summarize the aforementioned pattern, none of the coils exhibited a clear indication of dwell limiting below 10v with the exception of the D581 which showed a barely observable knee at 9v and 0c. This transition from non-limited dwell to limited was also temperature dependent, which is most pronounced with the D514a and D585 coils. In the spreadsheet any empty cells indicate there was no readily apparent dwell limiting at any amount of dwell (I went as high as 25ms in some cases). The exception was the -10c temperature range, where I had a limited amount of time to work and didn't get to re-test every coil at all the lower voltages I wanted. These cells were denoted with "n/t" (not tested).

Here's an example of the D581 coil which had the most easily recognizable dwell limiting waveform. The D580 exhibited a similar waveform when internal limiting was triggered.



The D514a coil exhibited a gradual reduction in primary current until reaching a minimum value where the current remained constant.



Here's the 8183 coil demonstrating a very noisy current waveform, which is a combined product of the voltage regulator I have that runs at 30khz, and the coils internal switching power section. Here's a waveform before limiting is evidenced.



And this is after - it's difficult to see but there is a quite pronounced falling edge to the current signal.



The "before limiting" waveform images for the 580 and 581 coils are included in the .zip for comparison.

As mentioned previously, the D585 coils exhibited what I'm going to call "absolute" dwell limiting. Because the waveform image won't really help visualize what was happening I'm not going to include one here, but there is an image in the .zip. For these coils I increased dwell until the current waveform stopped increasing on the scope's time scale. At this point it was clear that primary current was simply being switched off completely by the coil's internal circuitry, causing it to fire. I verified this by watching secondary current on the scope's second channel, which unfortunately couldn't be captured by my phone's camera in the same frame. Because of the effect of temperature on dwell limiting, in my opinion this coil doesn't present as much of a problem at cranking speeds as I initially thought. All that's needed is to stay at the minimum dwell for each voltage (8.4ms @ 10v, 5.8ms @ 11v, 5.5ms @ 12v, etc.) for safe operation. Obviously this doesn't give optimal charge time at higher temps, but I'm certain it would work adequately for the current design without temperature compensation.

At this point I think my next plan of attack is to test whether the controller will cleanly read the coolant temp thermistor voltage on one of the spare ADC input channels, and if so build out a full 2D dwell table for each coil targeting the maximum dwell from the test data, and interpolating the unknown cells - possibly with the help of referencing the factory coil-near-plug calibrations. Edit: on top of this I would add a simple RPM multiplier table to allow for reducing dwell with engine speed.

I know that this "good enough" type of effort is likely to cause kur4o to experience heart palpitations, but I'm not sure the amount of work needed to gather the data to implement such extremely accurate dwell control, especially in operating ranges that will rarely be experienced in the real world, is going to pay off in measurable results.

Another feature that's been proposed is multi-discharge. At lower RPMs and load (where spark advance high) there is an ample time window to implement a second spark fire after an abbreviated second dwell. It wouldn't be hard to implement either since it would be purely code additions. But after contemplating how to best implement it, I began to wonder why the OEMs aren't doing this already if the hardware they have is clearly capable of it. I'm still open to the idea of testing it, but I'm not sure I want to expend the energy at this point in the project. I'm mentioning it in the hopes that someone reading might have some experience with this and could add to the discussion.

Additionally, after what I was able to gather from researching the factory coil-near-plug calibrations, I'm not sure there's a compelling justification for implementing any MAP compensation. If anyone here can make a case for that I don't think there's any problem implementing a complete adder table, or leaving the current pumpshot type adder in place, please speak up. Because I see an unnecessary bit of wiring taking up an input that could otherwise be used for ECT, and code that if removed would streamline things.

Edit: Here's everything I have on the test coils that hasn't already been posted.

Coil Errata (16mb)