glow plug test

[tomcat]

looking for any help on glow plug replacment. I'd like to test (resistance) first but need to know which wires feed glow plugs. any help appreciated. I'v got a '99 f-250 7.3L here in Colorado that doesn't start w/o plugging in on these cold days

[mschn99]

Originally Posted by tomcat

looking for any help on glow plug replacment. I'd like to test (resistance) first but need to know which wires feed glow plugs. any help appreciated. I'v got a '99 f-250 7.3L here in Colorado that doesn't start w/o plugging in on these cold days

just to the passanger side and a little behind the fuel filter housing will be a relay that looks just like a starter relay. you are testing the two bigger posts on that relay. check it with the key off.....only one of the two bigger posts will have power. then have an assistant turn the key on while checking the one that did not have power.....it should get power when the key turns on and hold it for well over a minute if the relay is working properly. this is usually the culperate, although it could also be injector o rings, especially if this truck has sat for a long period without being started.....but that is way rarer than the glow plug relay..............Marc

[tomcat]

Checked the relay and test light stays lit for long time (minute or so) after key is turned on, and even after starting. I'm wondering if it's possible to check each glow plug (ohms) at the plug coming out of valve covers? I'd rather know for sure before I pull off valve covers and replace glow plugs.I'm sure they could use replacing by now anyways (104,000 miles).

[mschn99]

Originally Posted by tomcat

Checked the relay and test light stays lit for long time (minute or so) after key is turned on, and even after starting. I'm wondering if it's possible to check each glow plug (ohms) at the plug coming out of valve covers? I'd rather know for sure before I pull off valve covers and replace glow plugs.I'm sure they could use replacing by now anyways (104,000 miles).

go to the tech files under general forums. i posted a generic testing method for each individual glow plug there......but the answer to your question is yes, you can test each glow plug without pulling the valve cover. remember during your testing that it may not be a glow plug causing your problem....although it is a likelihood........dont just condemn that as your problem for sure.......Marc

[trrun]

Is it true if you start your truck before that glow plug light goes off it will shorten the life of your glow plugs? I owned a 01 dodge cummings and the manual for that said the manifold heaters would automatically shut off once ignition was started. Just wondering if glow plugs operated that way? Just wondering how many times fishing buddies started my truck without waiting, HAH,HAH. Tim

[mschn99]

Originally Posted by trrun

Is it true if you start your truck before that glow plug light goes off it will shorten the life of your glow plugs? I owned a 01 dodge cummings and the manual for that said the manifold heaters would automatically shut off once ignition was started. Just wondering if glow plugs operated that way? Just wondering how many times fishing buddies started my truck without waiting, HAH,HAH. Tim

your glow plugs do not operate once the motor is started. you will not hurt them by starting it before the light goes off, because they stay on even after the light goes off. the light is just an "edjucated" guess by the PCM as to when the plugs are hot enough to efficiently light the fuel......Marc

[trrun]

Thanks for the info Marc

[giafran]

i have a 2000 f250 7.3 i replaced glow plug relay last year.Bought two optima batteries two weeks ago, turn over great now i have to cycle it three to four times before it starts.I am afraid of it not starting at all is this normal or do i have a glow plug problem. ANY HELP FROM ANYONE WOULD BE GREATLY APPRECIATED

[95powerstroke5spd]

Your glow plugs are on from when you turn the key on to about 40 seconds after the engine is started. The glow plugs are the two outside pins on the valve cover harness connectors, resistance should be .5 to 2 ohms.