Uploaded May 2026 | Updated September 2026, 3 weeks ago

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Testing covered in this case study includes fuel pressure bleed-down checks, pump response during snap throttle testing, injector current ramp testing with a low-amp probe, checking for fuel pressure regulator leakage, interpreting early GM scan data, and using integrator/block learn fuel trim numbers to understand what the ECM is doing.

We also get into airflow sensor data, default strategies, substituted scan data, circuit operation from the wiring diagram, relay-controlled burn-off operation, scope testing power, ground, and signal circuits, and why before-and-after testing matters when dealing with intermittent symptoms and replacement parts.

This is a great example of slowing down, proving what is working, identifying what is not adding up, and being careful not to let trouble codes — or even a brand-new part — dictate the repair.

Part 2 will continue this case with a question every technician has faced: what do you do when the original repair only fixes part of the problem? Do you assume the diagnosis was wrong, work for free, or explain the next step and continue testing when a second issue shows up?


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0:00 Preview
0:30 Hot restart / long crank complaint
0:55 Fuel pressure testing begins
4:39 Checking for shorted GM injectors
7:40 Hot soak restart testing
9:25 Connecting to GM 12-pin DLC with an OBD2 Scan Tool
11:20 OBD1 MAF data and fuel trim analysis
15:18 Unplugged MAF default strategy testing
20:27 MAF burn-off circuit wiring diagram review
25:25 Scope testing the MAF burn-off circuit
29:44 MAF signal and ground testing
36:52 Rechecking the start/stall complaint
37:42 MAF replacement and throttle body cleaning
45:00 Testing replacement MAF sensor data — bad new part?
1:03:37 Used MAF sensor testing
1:11:07 Final Test Drive with Beau
1:13:10 Fuel Delivery Test using O2 at WOT
1:15:43 Importance of proper customer communication
1:17:37 What Did I Miss! There is another problem here

⚠️ Disclaimer:
ScannerDanner LLC is not responsible for misuse, unauthorized changes, or incorrect application of any information provided. Always follow proper safety protocols when using tools, equipment, or procedures discussed in this video. Use this content at your own risk.