Glow Plug Resistance Test
CAUTION:
The following test requires a high impedance ohmmeter (J-29125 or equivalent). Select scale values as follows: Left-hand switch - "OHMS" position; Right-hand switch - fully counterclockwise (200 ohms); Slide center switch - left position ("DC-LOW")
- Start engine, turn on heater and allow engine to warm up. Remove all electrical feed wires at glow plugs.
- Using a magnetic pickup tachometer (Mag-Tach J-26925 or equivalent), adjust engine speed. Turn idle speed screw on side of injection pump until engine idle is at roughest speed. About 860 RPM is desirable, but do not exceed 900 RPM.
- Allow engine to run for 1 minute at roughest idle. Thermostat must be open and upper radiator hose hot.
- 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. This ground wire must remain in position until all tests have been completed.
- Check resistance by touching positive lead of voltmeter to glow plug terminal (with engine running). Record value obtained in firing order sequence (1-8-7-2-6-5-4-3).
- 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 .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.
- 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.