DIY LTCC or similar system for LT1s

[spfautsch]

Wasn't able to get it to restart by giving it some pedal but ether worked. I suspect it would have stayed running had I given it a fatter shot of ether, but I'm not crazy about using it in my mostly closed, attached garage.

I attempted to start initially with both injector fuses pulled, then once coils stuck I put the fuses in, gave it a small hit of ether in the valve cover breather inlet on the TB, then restarted. It dies immediately but then restarts without removing power to the controller. The video is only one attempt but I was able to repeat this sequence three times in succession so it's not a fluke.

The first link is lower quality 5.3MB the second is 44.3MB at original resolution of the same attempt.

Low Q

High Q

I'm not considering this definitive proof something else isn't going on when these stick, but I see no reason an ignition system deficiency would cause it to start and then die on ether. And I'm otherwise extremely happy with general starting reliability - since adjusting my injector constant to what I feel is a more realistic number, starts have been spot on at all temperatures and conditions I've been able to test.

At any rate I'm going to seal up the wiring going through the acrylic so I can put it together and drive it. I should have a revision ready later tonight or tomorrow that will address the coil sticking during initial cranking.

[spfautsch]

Here's a fix release that addresses the coils being dwelled before the PCM has demonstrated control of the EST line.

I tested the issue in question and was unable to reproduce it at initial cranking with this firmware. I have a couple videos if anyone would like to see them. There may be the possibility of instances where a coil sticks at the end of a cranking attempt, but I've no intention of addressing that for what I believe to be very good reason. Also, initial startup will generally be delayed by another 90* of crank rotation from the last release due to waiting for the PCM to "light the fire" so to speak.

I didn't intend for this to be a major code revision, but when I started looking at how the high resolution and EST interrupts were handled it occurred to me they were being abstracted through the arduino namespace into somewhat less efficient constructors. This was eliminated. I'm going to call this an "interim" release because I removed a handful of references to pinMode() in this revision, and references to digitalRead() and digitalWrite() in the upcoming 0.9.41 revision. As near as I can tell, all that remains to make this compile within the Atmel AVR Studio is a suitable replacement for the arduino Serial object. But I'm not at all convinced there's good reason to do that. Anyway, the newer external interrupt handlers should honor the interrupt handling priority intended (EST being highest, then Hi Res input, followed by Lo Res input, then all others) when I originally conceived it.

What this revision does is basically hook the EST interrupt to a rising edge trigger at startup as well as after a stall / no-start condition occurs. As soon as a rising edge signal is caught and confirmed it switches the interrupt to using a falling edge trigger in order to catch the coil firing event. The "protection mechanism" is that whenever the interrupt 0 trigger signal is set to rising edge, no coils will be dwelled.

I've given this brief road testing. Will try to do more complete testing tomorrow - a clutch stall hot restart and a few other odbball cases. If anyone has more ideas for a testing "protocol" please post them!

[kur4o]

Did some test with new firmware and all seems good. I did one start with some idling till warmed up. Started within 1 second of cranking. Will do more tests of random cranking. On light throttle change I feel very little hesitation, On hard throttle change no hesitation at all.

[spfautsch]

I did one start with some idling till warmed up.

Are you meaning with engine running from all 8 cop coils, or some other testing configuration?

Started within 1 second of cranking.

This is not what I would call a good description of an LT-1 starting. I've had one somewhat "sketchy" start since moving to the 0.9.40 release. Otherwise it's been great, but with maybe 90 degrees more crank rotation. I actually logged it and can see the EST line arming / going high and then firing before the first cylinder would have fired (but wasn't because no dwell). I might do a pass-through thing for this to get fire sooner because the issue is going to be flooding the engine before any spark is delivered. But I think you have some other issues. A full second of cranking is very long for a healthy LT-1.

Will do more tests of random cranking.

My suggestion would be not to worry a bunch right now about trying to make it break during startup with random "trickery". Unless your perception of 1 second (1000 milliseconds) is a lot different than mine, you have some other start related issue that's obviously happening with your stock ignition system also. You said it here "Started on the second try which is not unusual on my setup".

I may be completely out to lunch here, but I think your injector flow constant is way off in left field. I would like to say you can trust me but I can't. What I can say is that after about a year of trying to extrapolate my IFC by way of trim numbers and then settling on where I'm at now, it hasn't started this well since I put my Multec injectors in the storage tote.

On light throttle change I feel very little hesitation, On hard throttle change no hesitation at all.

Let's revisit this after you answer my first question.

[kur4o]

All 8 coils hooked up for the test.
There were total of 12 led events before it fired off and I got a led on second or third crank TDC which is pretty good.

It only takes some time to fire up only on first start, after it have been sitting for some time[First cold start]. I suspect fueling since I was seeing coil firing on the leds. After the first start it fires off almost immediately[0.3s range]. After it get soaked on the first short try. It fires off immediately on the second try. I might play with FIC constant or first prime pulse.

[spfautsch]

It only takes some time to fire up only on first start, after it have been sitting for some time[First cold start]. I suspect fueling since I was seeing coil firing...

I personally think you have a badly leaking injector, fuel pressure regulator, or bad check valve in your fuel pump. But it could be anything. Unfortunately without having known perfect fuel injector data, it's going to be very difficult to surmise where the problem is.

Whatever the case, for the benefit of everyone else watching this thread, kur4o sent me a PM of a video of his start attempt. Out of respect for his privacy I'm not going to share it. But I do plan to go over it frame by frame. My initial impression is that I have no reason to doubt it. So I think we have a winner!

kur4o let me know via PM how I can get the prize to you and in what form you would like it (if other than 100 USD).

More importantly let me know how it goes when you try to re-start it after cool-down, etc.

I think I'm going to go start mine if only for amusement purposes. My neighbor already refers to it as "the engine" so what harm could come of some more punishment of their aural senses?

[spfautsch]

Here's another release.

0.9.41 - 9/22/2020

Removed all references to arduino digitalRead() and digitalWrite()

Added EST passthrough in EST rising edge interrupt handler for faster first dwell

Increased MAP vs RPM multipliers slightly in cruising range

I've driven this about 275 miles without major incident. Mileage on the last fill-up was 24.3 mpg, which was somewhat surprising since I haven't exactly been babying the go pedal. Cold starts have been a little slobbery, but the ambient temp has been dramatically lower in the mornings the past week or two. Then this morning it set a DTC43 when starting, which cleared on it's own after a few seconds of runtime.

I was somewhat concerned with this DTC when I hooked up my laptop to see what it was, because eehack has a description of "ESC Failure" for it. But EagleMark's original thread [here] describes it as a "Knock Sensor (KS) Circuit". So not sure what to make of this. I haven't seen the CEL light with the engine running in around 2 years. I didn't even think the '95s were equipped to sense a disconnected knock sensor circuit??? Would love to have a better description of what this DTC trigger conditions are but haven't been able to locate where these live in the 2000+ pages of the FSM. Whatever the case I'll report back if it reoccurs.

Still haven't heard anything further from kur4o - hoping everything's well. I'd like to get you your prize money and hopefully try to see if we can further investigate the light acceleration stumble you mentioned. That is, if your rig is still in running order...