DIY LTCC or similar system for LT1s

**vilefly** · 11-01-2017

1) it will start, but in simultaneous double-fire mode (1x inject per revolution). Since it has a distributor, all it need to do is fire the coil on the leading edge. The IAC will have to open up to compensate for 0 degrees TDC timing, so it may start and die unless the throttle is held open a little and set down slowly.
I might have to disable the hi-res signal and break out the timing light to confirm if it really is 0 deg base timing.

2) I don't believe there is a memorized cam position, but a programmed one might exist, but not applicable in this fail-safe mode of operation.

Hope my waveform posts on page 8 were helpful.

**spfautsch** · 11-01-2017

Originally Posted by vilefly

Hope my waveform posts on page 8 were helpful.

There was definitely some useful information in page 8 and 9 that I missed. Re-reading...

Originally Posted by vilefly

1) it will start, but in simultaneous double-fire mode (1x inject per revolution). Since it has a distributor, all it need to do is fire the coil on the leading edge. The IAC will have to open up to compensate for 0 degrees TDC timing, so it may start and die unless the throttle is held open a little and set down slowly.
I might have to disable the hi-res signal and break out the timing light to confirm if it really is 0 deg base timing.

2) I don't believe there is a memorized cam position, but a programmed one might exist, but not applicable in this fail-safe mode of operation.

Are you sure this is actually a fail-safe mode and not an unintended coincidence? I'd love to have confirmation that it will run like this - with batch fueling I can't imagine it would run very well.

The batch fire / double fire explains some of difficulties I had with the startup afr tables after an injector swap.

In consideration of your timing light experiment, do you have a keyed balancer hub? It's one of the items I need to put on my winter to-do list.

**vilefly** · 11-02-2017

Originally Posted by spfautsch

There was definitely some useful information in page 8 and 9 that I missed. Re-reading...

Are you sure this is actually a fail-safe mode and not an unintended coincidence? I'd love to have confirmation that it will run like this - with batch fueling I can't imagine it would run very well.

The batch fire / double fire explains some of difficulties I had with the startup afr tables after an injector swap.

In consideration of your timing light experiment, do you have a keyed balancer hub? It's one of the items I need to put on my winter to-do list.

GM always used simultaneous double-fire (all injectors per 1x rev) when starting on prior years, but to blast the shadow of doubt into oblivion, I will see about getting a waveform to prove it. We are crazy-busy at work, so it may take some time to get. My other injector waveform proves the cranking strategy, though.
My harmonic balancer is marked at 0 deg, as I was testing fitment of my northstar crankwheel project. I will probably use the hi-res waveform to prove exact timing.

**vilefly** · 11-02-2017

Ok. More codebreaking done. I used the previously posted northstar crankwheel data array to make a
ignition module "stimulator" program to be compiled by Arduino IDE. I haven't had time to test it on an ignition module yet.
Pins 2 and 3 will be the crank sensor outputs. 2= "A" and 3= "B" crank sensors.
4,5,6,7 are the coil selector outputs/indicators.
All outputs have been tested as best as possible w/o a module.
Remember to put a small value ceramic or polyester capacitor between the Arduino outputs and the Ignition module crank sensor inputs to simulate an ac voltage signal so that the zero-crossing detector in the Module will work.

Code:

int nstar[] = {1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0};
  // there are 0-95 elements, position 0 = 1st pulse from crank sensor A
  // crank sensor B = lags behind A by 7 positions
  // position 2 = cyl 1-4 TDC
  // position 18 = cam sensor pulse
  // position 26 = cyl 2-5 TDC
  // position 50 = cyl 7-6 TDC
  // position 74 = cyl 3-8 TDC
  // approx 3.857* per position
int crank1 = 2;  //pin2 = cranksensor 1
int crank2 = 3;  //pin3 = cranksensor 2
int coil = 4;
int x = 0;
int y = 0;
void setup() {
  Serial.begin(9600);
pinMode(crank1,OUTPUT);
pinMode(crank2,OUTPUT);
pinMode(4,OUTPUT);  //coil 1
pinMode(5,OUTPUT);  //coil 2
pinMode(6,OUTPUT);  //coil 3
pinMode(7,OUTPUT);  //coil 4
pinMode(LED_BUILTIN,OUTPUT); //enable the built-in led
}

void loop() {
  // put your main code here, to run repeatedly:
    for (int x = 0; x < 96 ; x = x + 1) {
      Serial.print(x);
      Serial.print(" ");
    if (x==2) {digitalWrite(5,HIGH); digitalWrite(7,LOW);};  //coil 2 enable   coil 1 disable
    if (x==26) {digitalWrite(6,HIGH); digitalWrite(4,LOW);}; //coil 3 enable   coil 2 disable
    if (x==50) {digitalWrite(7,HIGH); digitalWrite(5,LOW);}; //coil 4 enable   coil 3 disable
    if (x==74) {digitalWrite(4,HIGH); digitalWrite(6,LOW);}; //coil 1 enable   coil 4 disable
    if (nstar[x]==1) {digitalWrite(crank1,HIGH);
    delay(3);
    digitalWrite(crank1,LOW);}
    else {digitalWrite (crank1,LOW);}
       y = x+7; 
    if (y>=96) {y=y-96;}
    if (nstar[y]==1) {digitalWrite(crank2,HIGH);
    delay(3);
    digitalWrite(crank2,LOW);}
    else {digitalWrite(crank2,LOW);}
   // digitalWrite(LED_BUILTIN,HIGH);
  //delay (3);
  //digitalWrite(LED_BUILTIN,LOW);
  }
Serial.println("");  
}

**spfautsch** · 11-02-2017

I performed a few tests tonight, and think I've been laboring under flawed assumptions.

I wasn't able to determine pins readily at the opti pigtail connector, and though my 22 year old harness is a bit discolored I wasn't seeing anything similar to blue so I just determined the pins by trial and error. With a DMM I found ground and +12v with key on. The other two pins went to +5v which I made the assumption were the ECM's opti inputs. I removed the male connector end from the pigtail side of the connector.

The first one I disconnected appeared to be the low res pin, because it cranked but nothing was happening - no RPM change in the ALDL, and it immediately set DTC16.

I cleared the DTC, reconnected low res and disconnected high res. This time i was seeing RPM changes in the ALDL data, but no codes, no fire, nothing.

I would love for someone to confirm or disprove. I wonder if the presumption that the engine would fire without high res signal came from the pre-94 LT1s that were batch fired and didn't need to sequence anything. In the case of my having witnessed it start with the high res code, it would have to have been a case where the high res phototransistor was working well enough during cranking for the ECM to determine sequence. As I think I mentioned, mine would only re-set the code when the engine got to temperature.

What I'd like to find out is what happens when the high res signal is removed while the engine is running, but I don't currently have the connectors to allow this without cutting wires I don't want cut.

At any rate, I'm going to labor under the assumption that we need high res to determine sequence. I hope to post a sketch soon.

**vilefly** · 11-02-2017

Does yours have a front crank sensor on it or not? I imagine if it did, it would still start with the hi-res disconnected.
Here's a tool kit that everyone should have.....
https://www.toolsource.com/terminal-...t-p-54385.html
the thexton #392 micro/metric pack jumper wire set.

**spfautsch** · 11-02-2017

No that was only on OBD-2 cars.

**kur4o** · 11-02-2017

Originally Posted by spfautsch

I performed a few tests tonight, and think I've been laboring under flawed assumptions.

I wasn't able to determine pins readily at the opti pigtail connector, and though my 22 year old harness is a bit discolored I wasn't seeing anything similar to blue so I just determined the pins by trial and error. With a DMM I found ground and +12v with key on. The other two pins went to +5v which I made the assumption were the ECM's opti inputs. I removed the male connector end from the pigtail side of the connector.

The first one I disconnected appeared to be the low res pin, because it cranked but nothing was happening - no RPM change in the ALDL, and it immediately set DTC16.

I cleared the DTC, reconnected low res and disconnected high res. This time i was seeing RPM changes in the ALDL data, but no codes, no fire, nothing.

I would love for someone to confirm or disprove. I wonder if the presumption that the engine would fire without high res signal came from the pre-94 LT1s that were batch fired and didn't need to sequence anything. In the case of my having witnessed it start with the high res code, it would have to have been a case where the high res phototransistor was working well enough during cranking for the ECM to determine sequence. As I think I mentioned, mine would only re-set the code when the engine got to temperature.

What I'd like to find out is what happens when the high res signal is removed while the engine is running, but I don't currently have the connectors to allow this without cutting wires I don't want cut.

At any rate, I'm going to labor under the assumption that we need high res to determine sequence. I hope to post a sketch soon.

That`s happening because when high res dtc is set eside processor is trapped at infinite do nothing loop.
If you unset high res dtc bit at 12029 bit $10, you may try again runnig with high res disconnected.
I am pretty sure it will at least fire up and all the calculations will be time based on the low res signal. It will work just like the older distributor system with coil pick up signal. Of course spark scatter will be higher and timing will be not very accurate and we will lose the great starting time of less than a second.

**spfautsch** · 11-02-2017

Originally Posted by kur4o

If you unset high res dtc bit at 12029 bit $10, you may try again runnig with high res disconnected.
I am pretty sure it will at least fire up and all the calculations will be time based on the low res signal. It will work just like the older distributor system with coil pick up signal. Of course spark scatter will be higher and timing will be not very accurate and we will lose the great starting time of less than a second.

None of this compels me to want to code to time based sequence detection. At least not for a proof of concept. What are your thoughts? Does the Delteq system require high res?

**vilefly** · 11-02-2017

Just confirming obd-1 status. I will see if I have time to see if my 95 caprice does anything different. probably next week I might have the time at work.