How to test glow plugs on diesel engines 

Check the fuses, is a simple start. Do the glow plugs still operate?

No, you're testing the current draw of the glow plugs themselves, disconnected from the rest of the system. If you turn the ignition on the rail or the wire disconnected from it will become live and may arc on an earth and blow a fuse.

This is the fast way to do it. We're also not testing for continuity, we're testing for current draw. If you were to do that with multimeter, you would connect in series into the circuit for each glow plug. This is a quick test we use in the workshop to prove glow plugs are dead. If this didn't give us the results we were expecting, we would then go into more in depth testing (as explained in the video).

On cold starts the motor will start rough, misfiring and blowing smoke out the exhaust

@@gettingitdone1 ok thanks I'm getting them symptoms misfire rough start but no black smoke and po674 code thanks

First two things to look at. Are you fitting genuine glow plugs? I know we've had some aftermarket plugs that have short life spans, generally made in China. Also make sure everyone using the vehicle knows how to use the glow plugs properly for the full amount of time the light is on. If they aren't used properly they can get damaged on start up.

Yea usinging boch plugs from supercheap or Part Master, have used a different brand aswell incase it was that reason. I'm the only one driving it so im starting it correctly. The head got replaced in 2018 by a mechanic and the glow plug issue started after that. It's a 2006 2.5lt courier. The plugs look really black and sooty though. Seen this before?

@@kyle2956 haven't come across issues after head replacement. Can't think what would cause that, unless maybe it has leaking injectors? I prefer to fit NGK to couriers as that's what Ford use, and the do have a lot of issues. Next time I'd try getting a set from a Ford dealer and see how they go. Also check that the light isn't going out too early. Can you hear the relay click off when the light goes out?

@@gettingitdone1 My ‘99 Ford E450 was having starter trouble where sometimes there was no cranking on its old ignition wire so we ran a separate line directly to the ignition system and installed a momentary button in parallel and it started right up… but now that I read this could our “hot wire” solution be causing damage to the glow plugs because it bypasses the computer and any protective temperature sensors? Because this week my “engine died” (!) at 220,000 miles some of the indicators for bad plugs along with less and less power until now it just barely creeps at 1 mph. My mechanic wants to replace the engine but I’m wondering if we’re abusing the glow plugs into a bad state. Any thoughts?

No spark plugs in diesel motor. Only glow plugs which do a completely different job. Are you looking for spark plugs in a petrol or diesel vehicle?

Not quite sure what you mean there?

There might be some rare ones rated that low, but this technique is still perfectly fine. It's a very brief touch and the high current draw of the plug will easily absorb the spike.

Even if you did accidentally catch an earth somewhere, the chances of damaging an ECU like that would be extremely minimal. Maybe if you were dumb enough to hold it to the earth for a long time, even then you'd probably burn your hand first.

It's really not. Not sure what you think would be dangerous about it.

Touching the body ground with hot wire :D

I can never tell if these comments are pointing to something misspelled in the closed captions, or just a dig at my accent. But that's a lot of question marks. Is there an actual question here?