1989 F-350 Diesel Glow Plug Problem

My glow plug light comes on, but for only 6-7 seconds. After that, the relay on top of the controller starts clicking about once every second until you turn the key off. If you crank for an extended perior of time, the engine will start, but it smokes for a few seconds, I assume from all of the unburned fuel it is dumping into the engine. I was told it was the glowplugs. I checked and I had three of them that were bad and I replaced them. It started fine and I drove it that night. The next morning when I got in it to go, it wouldn't start. I checked and all of the glow plugs were bad. I checked even farther and there was constant voltage to all plugs even when the key was off. I took the advice of a friend of mine who is a "mechanic" and have replaced the glow plugs, controller and relay without any change in the situation. I have received other advice from the same mechanic, but before I replace anymore expensive parts for no reason, I was wondering if anyone has had this same problem or may know what I should do. This is a great truck in great shape with only about 100,000 and I hate to get rid of it. HELP!!!!! jwise271@yahoo.com

After you changed the controller and relay do you still have constant power to the glow plugs or is it that the bad glow plugs don't work. This makes a difference on what could be causing the problem.

I checked the voltage to the glow plugs and now it does not seem to have constant voltage. When the key is turned, it still lights up the plugs for about 7-8 seconds or so and then the relay begins to cycle on and off about once every second, continuing to do so until you turn the key off and will not let the engine start, it just cranks. I don't know what else to check. Could it be something as simple as a sensor or something??? Thanks in advance for your help.

Jon

I will try again tomorrow to find my manual as this Ford's system is different than I'm used to working on. I have worked on your trucks type and it is different.

Use a 12 volt test light hooked to the battery positive. Touch the tip of each glow plug the light should light.
With ignition switch in off position remove leads from glow plugs. Check continuity between glow plug terminal and power source.
Squeeze sides and lift check continuity between glow plug lead and test terminal.
Connect ohm meter between ground eylet and ground post on each battery.should be less than 1 ohm
Ignition switch off position check voltage at control unit power terminal.
If less than 10 volt service wiring.
If you have a fax machine send me a private email with the number and I will fax you a copy. It has about 12 pages and will eat up more than your email space.