Slow cold starts and persistent white smoke can be caused by failure of one or more glow plugs on indirect injection (IDI) engines. Test individual plugs with the ignition off and a low-voltage ohmmeter connected between the plug terminal and a good engine ground. Most draw about 2 !1 hot, and nearly 0 !1 cold. If the heating element is open, resistance will be infinite.
An open supply circuit denies power to all glow plugs and makes cold starting virtually impossible. Check for blown fusible links verify that the relay, often a solid- state device with an internal resistance that drops glow-plug voltage to 6V, is func- tional. EMS glow-plug controllers vary plug on-time with ambient and coolant temperatures. See Chap. 11 for details.
Excessive backpressure can prevent starting, cost power, increase exhaust tem- perature, and color the exhaust. Water locks—exhaust pipe risers to block water entry on marine installations—should not be used with turbocharged engines.
Look for damaged mufflers and flattened, crimped, or improperly sized exhaust piping. Trouble codes should be flagged if the EMS senses a clogged particulate trap or catalytic converter.
If excessive backpressure is suspected and the source is not obvious, drill and tap a 11/32 in. hole on a straight section of exhaust piping 6–12 in. downstream of the tur- bocharger. Tap threads for a 1/8 in. pipe fitting. Connect a manometer and, with coolant temperature normal, apply the maximum possible load to the engine. While backpres- sure varies with the installation, readings higher than 3 in./Hg are cause for concern.