Glow Plug Resistance Test
- Start engine and allow to warm up; then remove all glow plug wires. Using idle speed screw on side of injection pump, adjust idle to roughest speed (but do not exceed 900 RPM). Allow engine to run for 1 minute.
- Attach jumper wire between voltmeter ground lead and engine lift point on left side of intake manifold. DO NOT use any other point for ground connection. Check resistance by touching positive lead of voltmeter to glow plug terminals (with engine running). Write down values obtained in firing order sequence (1-8-4-3-6-5-7-2).
- If ohm reading on any cylinder is about 1.2-1.3 ohms, make a compression check on that cylinder before continuing fuel injection diagnosis. Most cylinders should measure between 1.8-3.4 ohms. If more than 0.3 ohms difference is observed between 2 consecutive cylinders in firing order, remove injectors and check opening pressure.
- To improve rough idle, switch nozzles as necessary. Install nozzles with a higher opening pressure to lower ohm reading, and a lower opening pressure to raise ohm reading. A change of about 30 psi will vary ohm reading by 0.1 ohm.
- Repeat procedure to confirm idle improvement. Be sure to check glow plug resistance at the same idle speed both times. If no improvement is observed, injection line replacement or injection pump calibration may be necessary.