DIY LTCC or similar system for LT1s

[spfautsch]

All good info, thanks guys. I hadn't given much thought to the possibility of thermo-mechanical stress problems from hard potting. The catalyzed silicone sounds intriguing, but I may go with some combination of silicone around the soldered components and epoxy over that for impact resistance for mine.

I didn't see any mention of a tach driver in those diagrams, but at least the colors match what I have. For now I'm going to labor under the assumption that the 94-96 Y bodies have a digital gauge cluster. Edit 2: found an addendum to the ltcc install document stating that only a few LT1 cars had the tach driven off the coil - 92-94 y bodies and 93 f bodies. Sweet - sounds like I can eliminate that with conditional compilation for those who don't need it.

I'm sorry to report I haven't made much progress over the last few days but I did get about an hour on it yesterday during which the outside temp dropped from 62f to 32f finally settling in at a balmy 16f. It's back to "stupid" cold. :-\

After cleaning up some changes I hadn't debugged fully I was able to get a better picture of what the microcontroller is seeing. This looks likely to be a case of the EST line causing induced or capacitively coupled noise on the low res input. Edit: the test coil was disconnected at this point so the microcontroller was only driving leds.

R1000:S29:D27:C1:E0:L0
R1000:S29:D27:C4:E1:L0
R1000:S29:D27:C3:E1:L0
R1000:S29:D27:C6:E1:L0
R1000:S29:D27:C5:E1:L0
R1000:S29:D27:C7:E1:L0
R1400:S29:D37:C1:E29:L0 << looks like low res rising edge is caught about 29 degrees early here - eerily similar to spark advance
R600:S0:D16:C8:E59:L0 << low res falling edge is then delayed another 30 degrees
R1000:S29:D27:C4:E59:L16
R1000:S29:D27:C3:E0:L0

If I decide to brave the cold tonight I'll try some external pullup resistors on these inputs since the AVR's built-in pullups are advertised to be in the neighborhood of 20-40K ohms.

Another possible source of noise may be a ground loop - I added a power ground for the microcontroller to one of the fuel rail bolts but didn't disconnect the other ground at the opti pigtail connector. I'm open to suggestions on what the best practice is here - do I need some type of filter for this secondary signal ground or should I do away with it?

[dzidaV8]

LT1 PCMs have separate Tach output, so don't worry about that function.

[Fast355]

LT1 PCMs have separate Tach output, so don't worry about that function.

The flash based LT1 PCMs do, the older chip based LT1 ECMs do not.

[spfautsch]

The flash based LT1 PCMs do, the older chip based LT1 ECMs do not.

Thanks, that's exactly what I was looking for! Shouldn't be an issue either way, there are plenty of open pins so I'm using the tach driver output to display the state of the EST input when in input test mode.

Just in case, I would check the alternator output for ac voltage ... Since the optispark runs off of 12V, I figure this could help.

I think I've got it sorted out, it wasn't a power problem. I just didn't know where the 12v power to the opti was connected to so I wanted to eliminate any doubt about adequate power. The extra signal ground from the opti pigtail also wasn't the apparent cause of the noise.

I ended up with 4.7k pullup resistors on the opti pins with a 1000pf cap on the low res input, and a 10k on the EST line. Oddly, 4.7k on the EST line set a "EST Open" code - 41 if memory serves.

I suggest running your coil trigger outputs through a buffer IC with 8 input/outputs. I think the proper term is "unity gain amplifiers", but they will probably be sold as buffers.

I'm opposed to growing part count unless absolutely necessary. When you test, if you can find a need for driving the coils w/ buffers we'll look into it.

The LS2 coils I have apparently have a very low current requirement on the igniter pin. I'm feeding mine through a 470 ohm resistor in series to the arduino pin. I'm also driving the sequencer leds from the arduino pins directly. I've noticed no issues thus far, but I'll save any further comment for when I've been able to bring the engine up to temp with the system.

Here's about a minute worth of video demonstrating cylinder #4 driven by the system with the opti running the other 7 cylinders. Once again, apologies for the shoddy camera work. I have no aspirations of becoming a videographer, amateur or otherwise.

Zip of logs here.

[vilefly]

I have to agree to low parts count. Nice video. Got a question. Is your LS1 ignition coil hooked up the the same + lead that feeds the ignition coil? I know the ignition coil feed has a noise capacitor on it right at the coil. Other manufacturers do this too. Try using the V+ feed for the OEM ignition coil and see if your noise goes away. The inductance of he other coil may dampen some noise as well. The ignition module may have other noise-dampening circuits in it (on the shared positive side), such as a zener diode or something. No extra parts required.

[spfautsch]

Is your LS1 ignition coil hooked up the the same + lead that feeds the ignition coil? I know the ignition coil feed has a noise capacitor on it right at the coil.

Yes, and I'm relatively sure there's nothing like that on my '95. Last weekend I stripped the tape off the entire right side harness from the #8 injector to where the MAF sensor branches out including all of the ignition feeds and there's nothing but wires and connectors.

If I can find all my old spark plug wires I'll try firing it with the original ignition system disconnected tonight. Fingers crossed, bunghole clenched...

[spfautsch]

As my videography skills run, I accidentally deleted the crank / start segment from my phone. It was unimpressive because I'd already started it twice before - once so I wouldn't drop my phone in the event the engine came apart and I soiled myself, and the second time my wife was "helping" with the video. The valves had warmed up by #3 so it was a bit of a long crank as I suspect it flooded slightly. After the final video when ECT was around 60c I re-started it and it fired off just as vigorously as we're all used to.

At any rate, proof of concept at long last. Also, revel in my woodworking skillz (temporary coil brackets).

Short clip revving (haven't looked at the logs to see peak rpm).

90 second clip showing eehack when it switched to closed loop. At the end I walk around and pick up the disconnected ICM and coil connectors as well as the opti coil wire.

Logs


After disconnecting the ICM plug, DTC 41 set immediately as it did when I was using a 4.7k pullup. So I suppose I might need to try a zener diode or something on this pin to keep the ECM from freaking out.

I'm stoked to have gotten this far. There's still a lot of work, but that's all going to be dead nuts fun for me.

What still remains to be seen is what the Atmega will behave like the first time I get stuck in St. Louis traffic on a 95F day.

I'm going wander over to my neighbor's place, have a couple glasses of bourbon and come home and sleep like I haven't in a few months. I'll do some research tomorrow and try to decide how to publish the source code.

[vilefly]

Just in case, I would check the alternator output for ac voltage and voltage drops from the positive lead to the alternator connection. Mine had some issues, and I added an extra positive connection to the underhood fusebox when I replaced and upgraded the alternator. Since the optispark runs off of 12V, I figure this could help.

I tested the optispark with a regulated 5v power supply, and it worked. It was a few months ago, so I hope I am remembering it right. With a clean power supply to it (grounded to the power supply of the controller), it could help eliminate any 12v entanglements.

I wonder if feedback was designed into the coil drivers like nissans do. One can hook an oscilloscope to a nissan's coil trigger signal and see a 5v representation of the secondary output. Kinda neat, but can cause problems if you are not ready for it. I suggest running your coil trigger outputs through a buffer IC with 8 input/outputs. I think the proper term is "unity gain amplifiers", but they will probably be sold as buffers.

Probably could use a big, fat capacitor right at the controller for anything else I missed.