DIY LTCC or similar system for LT1s

[spfautsch]

Found and fixed improperly handled array bounds logic in all three table lookup routines that could have impacted any min/max transition adversely. Sweep test framework has been added as a conditional. Somewhat embarrassed to have put this out for consumption by the general public, but then again it's code that makes a v8 run to beyond 6500 rpm without a mechanical distributor and it cost you nothing to download.

Drove the fixes home over my normal 63 mile "back roads" route and the butt-dyno was not disappointed. Idle seems to be slightly more stable and overall torque was more authoritative / bordering on brutal in the mid-2000 rpm range.

Planning to add a dwell base adjustment - thinking "-" globally decreases the map vs rpm multiplier table, and "+" increases it. So ten "-"s fed into the uart would adjust the base multiplier from 128 to 118 and vice versa.

Will try to get this ready for public consumption early next week.

[spfautsch]

0.9.43 tested, sig updated with link.

Disclaimer - I was not able to test above 6600 rpm in-car because I didn't want to come to a complete stop and shift into 1st. Next time I'll wait until 80mph in 2nd to let off. But I'm fairly certain the fixes will resolve any unwanted behavior.

Also added in this version (quite some time ago) is a 5.xxx volt constant in config.h for fine-tuning voltage sensing. kur4o if you have a 7-18v variable dc power supply and a lab quality multimeter, fine-tuning this to the nearest millivolt (3rd decimal place) gives best precision. If not, the default value will put you close enough.

The multiplier offset seems to work, though I've been unable to push it far enough to see an increase in map / decrease in responsiveness. This lets the user increase or decrease the entire map vs rpm multiplier table by a fixed positive or negative number. It resets to zero with loss of power.

After giving it some thought, it wouldn't be impossible to turn this into self-tuning routine that could find ideal dwell in cruising ranges, though it would require some damned careful steady-state driving.

[spfautsch]

Just wanted to update with more info. Fully tested to 6800 rev limiter, no abhorrent behavior.

Also, I tested the multiplier offset fairly extensively. Based on your observations (kur4o) I decided to lower dwell to the point I could sense a difference in idle. It didn't happen until about -84 (base multiplier 44) or about 70% [edit: below] of the test data "max" dwell target. Somewhere in the neighborhood of 1.1ms. Even drove on interstate @ 75mph as low as -78. I ended up scaling the 8183 dwell table by 0.6 across the board, and adding some minor tweaks to the map vs rpm multiplier table. Seems to put the average dwell target around 2.0ms in normal driving.

I put about 150 miles on this setup with another 50 already on the trip odometer since last fill-up and came out at 22.1 mpg even with several hard wot pulls, a 1/4 mile pass to 130-ish and 6-8 aggressive merges onto interstate (15-75mph @ 60-90% throttle). No noticeable change other than feeling some "surginess" around 1700-2400 rpm occasionally that seems to be a product of using too many floating point logging pids at 500ms intervals.

kur4o if you've got time I'd love to hear your impressions of using the multiplier offset and how the engine reacts to less / more overall dwell. I'd really like to figure out if it's possible to use one map vs rpm multiplier table or not. Though if I have to I can probably just buy a complete set of D514a coils. Maybe a set of D585s too. Though I'd really rather spend that money on paint and fixing the dying window regulator motor.

I'd also like to discuss some ideas for implementing multi-spark - i.e. what type of tables would make the most sense, when it should be disabled, etc. Obviously it will have to work within lower rpm ranges, based on coil charge / recovery time.

Meanwhile I'll try to plug away at the documentation. Have I mentioned how much I hate writing documentation?

[kur4o]

I really hope to test the update soon. It does sound really promising. WIth the possibility to dial on the fly some offset and test wot times with fatter and leaner dwell.
It also opened the door to some auto tune logic if there is enough cpu power, finding the best dwell, not sure what we can use for feedback.

I think the current table setup is workable enough and gives some edge over the traditional GM tables design. You will likely loose some rpm vs volts spread but within the usable 11-15 volts it is pretty acceptable.

Finding the weak points that can`t be worked out can gives us a better idea which coils will work best on the broader range. ANyway it is some hack job of very old technology and not all can be perfect.

For the multispark. We might need minimum off time scalar. The time the coil discharges. To take advantage we might just disable on rpm threshold, where the minimum 1.5 dwell at least cant be reloaded fast enough to give a spark before the piston reaches bottom.

We also need to find where will be the best time in degrees to apply the second spark. Something like an EOIT target but for dwell. I guess some realtime control for second spark delivery can gives us an invaluable feedback what needs to be done.

I will take a look at what is designed by gm and hopefully get some fresh ideas.

[spfautsch]

... WIth the possibility to dial on the fly some offset and test wot times with fatter and leaner dwell.

While I'd love to hear your feedback, if your transmission is struggling to deal with the torque you might want to lay off the WOT passes.

I will take a look at what is designed by gm (on the subject of multispark) and hopefully get some fresh ideas.

Sounds good.

I think the auto-tune idea may be premature. Unless / until misfire detection can be made to work reliably, I don't think there's enough feedback with only MAP info. Still, being able to adjust dwell on-the-fly was eye opening. I would have never thought to take more than 50% of the maximum dwell out in order to see / feel a change.

Will continue to focus my energy on documentation, time based (limp home) run mode, and misfire detection, in that order. I'm also pretty sure I'm going to go ahead and acquire a set of D514a and D585 coils to use for testing with my own butt-dyno.

[kur4o]

Just did some test run with the new firmware. No issues and running strong. Didn`t push it much. Did some fine tuning to get rid of some lean conditions.

It looks like the most important table for maf tuning is the so called maf pump shot coefficient. I came up with some really weird settings with real time control and now the car runs 100 times better on part throttle take off. Pulls really strong now.

I will do some write up how it works, and how I set it up. Even the wideband almost frozen and stopped jumping around.


I still have no definite answer how to set the multispark.

There are 3 scalars we need. Some 2d pulses vs rpm. Or 3 ranges 0-1000rpm 3pulses 1000-2000 range 2 pulses, above 2000-1 pulse.
Min burn time. The time the coil will discharge. And dwell time based on the pulse count or rpm count.
Also enable at crank only, at run only or always.

Not sure will there be any benefit of waste spark setup. So you fire each coil twice on a full crank rev.

[syntaxterror]

Outstanding work! I have one question with coding could this work on a obd1 v6 ?
Thanks Joe