My truck has trouble starting in temps below 45 degrees. If it's too cold, my truck won't start unless the block heater is plugged in, or if I spend ten minutes turning the key and pushing the gas pedal. When it fires up it creates a cloud of white smoke, and occasionally the truck idles so rough that it jumps as the tach bounces between 500-750. From what I know this problem is either due to bad glow plugs or a bad glow plug relay. How do I determine which is the culprit. Would it be a good idea to replace all 8 plugs? Also, does a bad glow plug result in decreased performance and fuel mileage? How much will it cost to fix the problem?

 

Jump the Relay from big post to big post for 10-15 seconds then fire it up, if it fires good, chances are it is your relay.

 

If you look at the top of this forum there is a glow plug and hard start trouble shooting guide. It will more than likely answer all of your problems. If you have a more specific question ask it. welcome to FTE

 

You can test each one individually through the wiring harness (valve cover gasket) with a volt meter. Outside pins on connector to positive on battery (inner pins are injectors). If the voltage is less by a volt or more than the battery voltage, you have a bad plug. If you are going to replace a plug on one side of the engine, do all of them on that side at the same time while the valve cover is off. One out, you probably won't notice. Three or more out it will start hard.

All the glow plugs do is get the engine running. After 30 sec - 2 min they shut off and do not affect engine performance. Nor do they affect fuel economy. The smoke and rough idling are from all the unburned fuel left in the cylinders. The cost is just under $10 per plug from Autozone - Use ONLY Beru/Motorcraft plugs! Glow plug relay is usually the culprit. Part# GPR 109 from Napa + or - $35. If you ask for the specific year and make truck, $60 - $90. Use walt1968's method or volt meter between two large terminals on relay when key is first turned on to check GPR. No voltage - turn on key - battery voltage for up to 2 min - back to no voltage would be a working relay. Sometimes they work intermittently before completely going dead.