docs: Document comprehensive voltage readings from John's notepad (2026-03-22)

- Added CKP sensor voltage readings: 10.9V power (good) vs 11.38V reference - Added CMP sensor voltage readings: 12V power, ground, signal all good - Added ICM voltage readings showing 0V trigger signal in bad van - CRITICAL FINDING: ECU not sending trigger to ICM (0V vs 6.3V in good van) - CKP power supply verified GOOD - not the problem - CKP AC signal test while cranking still needed - Root cause: ECU not firing coils despite good CKP power
2026-03-22 18:16:26 -04:00
parent efa71f47ec
commit acaafbfc9a
1 changed files with 122 additions and 4 deletions
@@ -34,10 +34,120 @@
 | Coil power | 12V battery voltage | TBD | ? | [YYYY-MM-DD HH:MM] |
 | Coil ground | Good ground | TBD | ? | [YYYY-MM-DD HH:MM] |

-### Diagnostic Data Collected
- **[Test 1]:** [Results and conclusions]
- **[Test 2]:** [Results and conclusions]
- **[Test 3]:** [Results and conclusions]
+### Diagnostic Data Collected (2026-03-22)
+
+**NOTE:** John provided detailed voltage readings comparing "good van" (2002 Chevy 3500 - working) to "bad van" (2002 Chevy 1500 - not starting).
+
+---
+
+#### CKP Sensor Voltage Readings
+
+**Good Van (2002 Chevy 3500 - Working) - Reference Values:**
+| Test | Voltage | Notes |
+|------|---------|-------|
+| CKP A+B (key ON) | 11.38V | A=12V reference, B=Ground |
+| CKP A+C (key ON) | 10.8V | C=Signal |
+| CKP A+B (key OFF) | 0V | No power |
+| CKP A+C (key OFF) | 0V | No power |
+| CKP probe (key OFF) | 0.17V | Signal voltage |
+| CKP probe (key ON) | 9.34V | Signal voltage |
+| CKP reference | 12V | Power from ECU |
+
+**Bad Van (2002 Chevy 1500 - Not Starting):**
+| Test | Voltage | Notes |
+|------|---------|-------|
+| CKP A+B (key ON) | 10.9V | A=reference, B=Ground |
+| CKP A+C (key ON) | 10.35V | C=Signal |
+| CKP A+B (key OFF) | 0V | No power |
+| CKP A+C (key OFF) | 0V | No power |
+
+---
+
+#### CMP (Camshaft Position Sensor) - Red Connector
+
+| Pin | Wire Color | Function | Voltage (Good Van) |
+|-----|------------|----------|-------------------|
+| A | Red | Power | 12V |
+| B | Br/w | Ground | Ground |
+| C | Pnk/b | Signal | 11.3V (A+C) |
+| A+B | - | Power+Ground | 10.7V |
+
+---
+
+#### CKP (Crankshaft Position Sensor) - Green Connector
+
+| Pin | Wire Color | Function | Voltage (Good Van) |
+|-----|------------|----------|-------------------|
+| A | Green | Power | 12V |
+| B | - | Ground | Ground |
+| C | - | Signal | 10.8V (A+C) |
+| A+B | - | Power+Ground | 11.3V |
+
+---
+
+#### ICM (Ignition Control Module) Voltage Readings
+
+**Good Van (2002 Chevy 3500):**
+| Test | Voltage |
+|------|---------|
+| ICM A+C (12V on) | 12V |
+| ICM A+C (10.2 start) | 10.6V |
+| A+B on ICM (0V off) | 1.2V |
+| A+B on ICM (12V on) | 12.1V |
+| A+B on ICM (7.4V run) | 10.6V |
+| A+C on coil plug (6.3V run) | 0V |
+| A+C on coil plug (0.5V off) | 0.5V |
+| A+C on coil plug (0V on) | 0V |
+
+**Bad Van (2002 Chevy 1500):**
+| Test | Voltage |
+|------|---------|
+| ICM A+C | 12.15V / 10.6V |
+| A+B on ICM | 0V (off), 1.2V (on) |
+| A+B on ICM | 12V (on), 7.4V (run) |
+| A+C on coil plug | 0V (run), 0.5V (off), 0V (on) |
+
+---
+
+#### Key Analysis
+
+**CKP Power Supply: ✅ GOOD**
+- Bad van shows 10.9V on A+B (key ON) vs 11.38V reference
+- CKP is receiving power (slightly low but close)
+- Ground appears good (0V with key OFF)
+
+**CKP Signal: ⚠️ NEEDS CRANKING TEST**
+- A+C = 10.35V in bad van (vs 10.8V in good van)
+- Slightly lower but could still be OK
+- **CKP is magnetic sensor - needs AC signal test while cranking**
+
+**CMP Sensor: ✅ GOOD**
+- Red (A) = 12V power
+- Br/w (B) = Ground  
+- Pnk/b (C) = Signal at 11.3V
+- **CMP has power and ground**
+
+**ICM Trigger Signal: ❌ PROBLEM IDENTIFIED**
+- Bad van shows 0V on A+C coil plug (run) vs 6.3V in good van
+- **ECU is NOT sending trigger signal to ICM**
+- Even though CKP has power, ECU isn't firing coils
+
+---
+
+#### Conclusions
+
+1. **CKP sensor has power** - The 10.9V reading indicates sensor is receiving voltage from ECU
+2. **CMP sensor has power** - All voltage readings good
+3. **ECU trigger to ICM is 0V** - This is the root cause
+4. **Possible causes:**
+   - CKP sensor not producing AC signal while cranking (need to test)
+   - ECU not processing CKP signal correctly
+   - Internal ECU damage from water intrusion
+   - Bad ECU (the eBay replacement is also bad)
+
+---
+
+**Next Critical Test:** Measure CKP AC signal while CRANKING - should see 0.5-2V AC if sensor is working

 ## 🎯 Theories & Root Cause Analysis

@@ -157,6 +267,14 @@
 - **[Date: Unknown, Few Months Ago]:** Initial diagnosis began - confirmed NO SPARK at all 8 spark plugs
 - **[Date: Unknown]:** Tested spark at ignition coil pigtail to distributor - NO SPARK
 - **[Date: Unknown]:** Removed connector from ignition control module (ICM)
+
+### Diagnostic Data Analysis (2026-03-22 18:13 EDT)
+- **[2026-03-22 18:13]:** John provided detailed voltage readings from notepad comparing good van (2002 Chevy 3500) to bad van (2002 Chevy 1500)
+- **CKP Power:** ✅ GOOD - 10.9V on A+B (key ON) vs 11.38V reference
+- **CMP Power:** ✅ GOOD - 12V on red wire, ground on Br/w, signal on Pnk/b
+- **ICM Trigger:** ❌ PROBLEM - 0V on A+C coil plug (run) vs 6.3V in good van
+- **Root Cause Identified:** ECU not sending trigger signal to ICM
+- **Next Critical Test:** Measure CKP AC signal while CRANKING (should see 0.5-2V AC)
 - **[Date: Unknown]:** **CRITICAL FINDING** - Grounded the signal pin from ECU to ICM → SPARK RETURNS
 - **[Date: Unknown]:** Confirmed ground is present at ICM connector
 - **[Date: Unknown]:** Confirmed battery positive is present at ICM connector