DIY LTCC or similar system for LT1s

[johnny_b]

It seems member dave w has come up with a solution for the vortecs to run the 0411 pcm. The project looks rather affordable and simple. it requires the use of a vortec distributor combined with his piece. It seems to me that this could be used on the LT1 by drilling a hole in the intakes the same way people do when they swap lt1 intakes on to tpi setups. I love EEhack so much id really hate to ditch the original pcm, and the ultimate dream for lt1 lovers, at this point with the amazing software already available, really would be coil on plug with the original pcm. but his project looks promising. just thought id share.

edit: after further discussion with dave w, his project will not support coil-on-plug at the moment.

[vilefly]

ok. I think I found a place that still sells the non-fashionable DIP-14 IC packages that I can work with. Jameco electronics still has the old ICs that I remember, and super cheap, too. I have placed an order to try out my schematic. Unfortunately, I already orded SOIC chip adapters also. Oh, well.
Has anyone used my northstar data array to generate a signal, yet? I am still reading about loops and stuff, despite being attacked repeatedly by "the Squab".

[vilefly]

So, Johnny, how's the northstar ignition module working for you? I still need to learn how to write a program to generate crank signals from the array I made. I was hoping you knew how, since I have over extended myself on solving multiple problems.
In case everything fails, I have a toothed northstar wheel designed in a DXF file that should bolt up to the harmonic balancer. I am working on the dual crank sensor bracket. This was inspired by the Indmar LT-1 ignition system installed in the Mastercraft boats. The waterjet cutter service would cost me about $80-$100 for one wheel. Less if I have more made, but I am still working it all out with no final design yet. The belt system goes on the left or right, depending on application. How inconvenient.

[spfautsch]

I revisited the thread tonight to catch up, and finally read the link in the second post pointing to chevythunder. I couldn't help but stumble several times on the description of the degree wheel.

and since the camshaft rotates once per two revolution of the crankshaft, it is in reality seeing 720 pulses.

Uh, no. Your math is bass ackward. It is true that the camshaft rotates once per two crank revolutions, but if the outer wheel has 360 slots it's only seeing 360 / 2 = 180 per crank revolution. Let's not get caught up on rising and falling edge signals here, but looking past one's interpretation of "pulses" it's getting 360 signals per crank revolution or 720 signals per cam revolution, max.

Like the outer ring, the ecm "sees" 16 pulses for each revolution of the camshaft

This statement is only correct if you consider "pulses" as both rising and falling edge, but why would we be thinking in terms of camshaft revolutions? As a person who's on the Asperger's spectrum, this drives me batty.

Unless vilefly beats me to it, I'm thinking my game plan for winter is giving the arduino a shot with the assumption of driving ls1 coil modules with 5v ttl signaling. I think this can be done without looking at the high resolution signal by keeping memory of the current position and calculating rotational speed based on the smaller of the lower resolution signals which the aforementioned page says are signaling 1,4,6 and 7. Another presumption I think can be relied on is where the crank comes to rest at engine shutdown. I've learned from talking to some white haired gentlemen who've seen their share of missing flywheel teeth that chevy v8s tend to come to rest in only about four different spots. In a case of the crank being jogged by a mechanic, if we assume the ECM follows the same logic, worst case the uC will miss the first or second cylinder firing after a power loss but so will the ECM with injection sequencing.

Am I making any grotesque oversights?

[vilefly]

nope, didn't miss a thing. It sounds like a game plan to me. I did wonder why they only synched using cylinders 1,4,6,7, but I think you may have answered that question. Resting position.
The TTL drive sounds like a winner to me, providing a current limiting transistor is used between the two, just in case. 15-20mA sounds safe to me.
I've been buying some Arduino Pro Mini controllers on ebay at about $5 each to tinker with. The very flexible compiler will let me use the same code on a different controller. Kinda nice, when building expendable projects where risk is high. Made some animated 8x8 led matrix eyes for my kid's halloween costume. Taught me a lot. Still, I borrowed heavily from the example code, but I am hooked.
The Pro Mini is the size of a medium postage stamp, and it just might be able to pull this trick off. Much more powerful than I expected.

[spfautsch]

I'm thinking a simple class d bjt amp powered by the ECM's coil trigger output for each coil. Or FETs if you want to get fancy (possibly higher parts count)? There are also some widely available stepper motor driver DIP ICs that may fit the bill.

My thinking is the uC employs a watchdog timer that triggers relearn. So we haven't seen an input change in a while, watchdog timer fires and says assume the engine isn't running anymore so set a bit in memory and go to sleep (power consumption can be an issue with the arduinos).

Let's assume that the stopping position is 20-30 degrees shy of tdc of a compression stroke. We're either going to be near 1, 4, 6, 7, or 8, 3, 5, 2. Let's also make a huge leap that this is not in a light gap in the wheel (logic low to the uC).

So the user cranks the engine.

The user engages the starter, and the uC picks up a rising edge interrupt that wakes it. We look at the "is it running" bit to see if we need to re-learn the position. We do, so we start counting microseconds until the next falling edge.

The falling edge signal happens and we store the microseconds in variable a.

Now we wait for the next rising edge signal. <thumbs twiddling>

Rising edge signal clicks. Now we count microseconds again until the next falling edge signal.

Falling edge signal happens. Store microseconds in variable b. Compare a to b.

if ( a > b ) {
  c = a / b;
  [ some code I haven't thought through completely]
  x = (next firing cylinder);
} else {
  c = b / a;
  [ some code I haven't thought through completely]
  x = (next firing cylinder);
}

Once the running bit is set the uC sequences ignition from memory based on the rising edge.

So you say what if the engine is parked in a light gap, and the first signal we see is a falling edge. Simple - set another bit that inverts the sequence detection logic [that I haven't thought out completely].

Easy peezy. I'll think about fleshing out the code on my drive to work tomorrow. There will need to be some fuzzy math allowing for variance in angular velocity during cranking. That's why they made the big gaps larger by multiples of 5.

[spfautsch]

After working this out mentally and doing some additional research on Arduino interrupt handling I've learned that accessing time functions inside an ISR appears to be a bit of a tangled subject. This would make it quite a bit "hairier" to detect sequence with only the low-res signal.

This got me wondering how the ECM behaves. If no-one knows I'll confirm myself when I have a chance, but I'm wondering if it will start after:

1) disconnecting the high-res signal
2) removing power from the ECM to clear learned cam position

I know it will start and run without the high res signal, but it was more than a few years back when I worked on replacing my opti sensor and I don't know if I ever disconnected the battery throughout that process. I don't believe I did.

If the ECM is improperly sequencing the injectors I would presume the engine may run, but poorly. If, on the other hand the ECM simply won't detect cam position or fire the injectors without the high res signal that simplifies things immensely. Detecting the position becomes considerably simpler and faster if we need only count high res pulses to determine a trigger slot's opening size.

[johnny_b]

So, Johnny, how's the northstar ignition module working for you?

Haven't had much time to play with anything, as I have about 5 weeks left in the semester.

Given Kur40 knowledge of EE if he thinks the northstar icm is a step back then it most likely is so I have abandoned that idea.

I'm still lurking on y'alls discussion though

good luck guys

[vilefly]

Haven't had much time to play with anything, as I have about 5 weeks left in the semester.

Given Kur40 knowledge of EE if he thinks the northstar icm is a step back then it most likely is so I have abandoned that idea.

I'm still lurking on y'alls discussion though

good luck guys

I tend to look at it as a half-step towards 1 coil per cylinder. It still eliminates the hi-voltage side of the optispark, which is the goal of all these
experiments. I would not use it for a top-fuel dragster, but on the street, sure.