Truck will not start unless we use starting fluid hot or cold

Check the glow plugs:

. Testing. Use an ohm (Ω) meter to check for continuity, which will tell you if the glow plug is shot, has continuity, or is worn. Ohm out each plug through the harness. Good glow plugs will have a resistance between 0.6 and 2 Ω. If you get infinite resistance on any plug, it is either bad or the connector under the valve cover is loose.

. Removal and installation. With the engine "stone cold," disconnect batteries, remove valve cover, disconnect glow plug connector, remove glow plug with a 10mm deep socket, install new glow plug (torque to 13 ft.-lbs.), and reattach connector. After finishing the remaining 3 glow plugs on that bank, clean valve cover, install new gasket, and reinstall valve cover (torque to 97 in.-lbs.). Do the same thing for the other bank of glow plugs and reconnect batteries. Not a difficult job--should take several hours.