No spark

I hate to ask this again, but are you certain the ground is good? I have had situations where I would have continuity to ground but when a load was placed on it, it would fail.

Let me know what you find. It's tough not being there. Regardless, I hope you have a good and safe new year tonight.

Take care,
Joe

I suspect then, the module is bad. Let me know when you get back to it.

Joe

I attached the schematics from the coil to everything it goes to. There are a couple fuses I want you to check, but I have my doubts. Regardless, let me know which color wire at the loses power. I am trying to trace everything for you, but something just isn't making sense for me. Take a look. To follow all the wiring related to the coil, I had to go across several pages. As a result, there are several pics. I did highlight the wires involved. The pics end at the VCM. There is one section where I circled two fuses. I figured it wouldn't be a bad idea to check them as well as to confirm power.

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Read through this description. Also, the last picture I attached is a GM schematic.

Circuit Description

The enhanced ignition system uses the crank sensor in order to provide the timing input to the VCM. The VCM uses this reference pulse in order to determine the individual ignition spark timing for each cylinder.

Once the VCM calculates the ignition timing, the ignition coil module on the IC circuit receives the timing signal. Each timing pulse received by the ignition coil module on the IC circuit triggers the coil module in order to operate the ignition coil. The secondary ignition voltage is induced, and then the secondary ignition voltage is sent to the distributor for distribution to each spark plug. This DTC is a type A DTC.

The IC signal voltage ranges from about 0.5 volt to 4.5 volts.

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Next, I don't know if you have checked for trouble codes, but doing more research, I came across this. The flow chart for testing is in the last three pics. It seems relevant.

1997 Chevy Truck C 1500 Suburban 2WD V8-5.7L VIN R
P1361
Vehicle ALL Diagnostic Trouble Codes ( DTC ) Testing and Inspection P Code Charts

Circuit Description
The enhanced ignition system provides the timing input to the VCM with a crank sensor. The VCM uses this reference pulse in order to determine the individual ignition spark timing for each cylinder.

Once the VCM calculates the ignition timing, the ignition coil module on the IC circuit receives the timing signal. Each timing pulse received by the ignition coil module, on the IC circuit, triggers the coil module in order to operate the ignition coil. The secondary ignition voltage is induced, and then the secondary ignition voltage is sent to the distributor for distribution to each spark plug. This Diagnostic Trouble Code (DTC) is a type A DTC.

The IC signal voltage ranges from about 0.5 volt to 4.5 volts.

Conditions for Setting the DTC
EST enabled, and engine speed is less than 250 RPM.

Action Taken When The DTC Sets
The VCM turns on the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids
A poor connection, a rubbed through wire in the insulation, or a wire broken inside the insulation will cause an intermittent.

Check for the following conditions:

Poor connection.
Damaged harness: Inspect the VCM harness connectors for the following conditions:

- Backed out terminals GR9 and BK18.
- Improper mating.
- Broken locks.
- Improperly formed or damaged terminals.
- Poor terminal to wire connection.

And

- Damage harness.

Intermittent test If connections and harness check OK, monitor a digital voltmeter connected between VCM terminal GR9 and Bk18 while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change. This may help to isolate the location of the malfunction.

Test Description
The numbers below refer to the step numbers in the diagnostic table.

2. If the engine starts at this point, the DTC 1361 is an intermittent.
3. This check determines if the IC signal from the VCM is available at the ignition coil module.
9. The remaining tests begins to check that the ignition coil module circuitry is OK. If the ignition coil module loses its voltage source, the secondary voltage will not be produced, and a DTC P1361 will set.

Let me know.

Joe

Wow! I'm glad you got it going. If you page back through our conversations, that was one of my main concerns. You got tricked like I did with a false positive ground reading. That is so frustrating. I went through a similar situation with a no spark issue. I would check continuity to ground and it looked great, but once a load was placed on it, it failed.

No matter what, you did one heck of a job. These types of problems are difficult even for those who have a ton of experience. The fact that you found the issue says a lot.

Take care and let us know if you have questions in the future.

Joe

You are very welcome. I have to be honest, I enjoy a good challenge like this. Please let us know if you ever have questions in the future.

Take care of yourself.

Joe