How to test glow plugs?

While I am in the midst of testing things how do I test the glow plugs to see if they are working?

The simplest way is with a test lite. From the positive and either battery directly to the glow plug electrical connecter. The other way is with an ohm volt meter. The digital type works better.

Am I just testing for continuity? So if I touch the test light to the end and it lights they are good, no light they are bad?

Need to use ohm meter. I cant remember what the reading should be for the good ones off the top of my head. Someone else will chime in but if not I will go out and test some of my new ones I have and post later.

forcefed said:

Need to use ohm meter. I cant remember what the reading should be for the good ones off the top of my head. Someone else will chime in but if not I will go out and test some of my new ones I have and post later.

Click to expand...

i thought as long as there was resistance they were good, if they're open they've gone south?

-Jon

That's what I am trying to figure out

the less ohms the beter shape they are thats what i was told today by a diesel shop

I didn't make it out to test but you should have no more than 3 ohms I would say. Like said above the the lowest ohms are good and if you have no reading at all they are bad.

Or if your stuck in the woods, just get a wire on to the battery + and with other end of the wire just strike it like a match on the GP terminal. if you see small sparks its working if not its dead

icanfixall said:

The simplest way is with a test lite. From the positive and either battery directly to the glow plug electrical connecter. The other way is with an ohm volt meter. The digital type works better.

Click to expand...

with the key on or off

Don't you have to unplug the GP and touch the top of it with the test light....if you don't do each one individually unplugged, the other's will provide a ground to light the test light up.

Volt meter on DC amps, hook black negitive on the positive battery post, unplug the wire to the glow plug, touch the red meter lead to the top of glow plug, meter should read 4 amps.

Hold for 5 seconds, good amp draw = good plug under load.

The amp draw will spike up to like 6 amps then level down, the hotter the glow plug gets the lower the amp draw, ohm's law, 12 divided by 3 = 4 amps.

I've always tested them out of the truck but I hate pulling the things only to find out they are good. So I'm going to try Tim's way of doing it. Hopefully this way I'll be able to find a couple bad ones with no need to pull all of them.
My truck started terrible this morning because it was -10* and after the 3rd time of attempting a start and having it die a couple seconds later I let everything cool down and did a 20 second burn, and then still had to hold onto them for another 5 seconds or so after it fired up to keep it running. I think I fried some.

I check them the way ford has me test them and it has never failed. The test light trick will work in a pinch but isnt a proof positive ( I have had non-beru plugs light the test light but not get hot)

Using a volt meter (digital preferred) set it to ohms (resistance). Place one lead on the block and the other to the tip of the glow plug where the electrical connector goes. You should get 0.3 -0.8 ohms resistance for our trucks. I would think some glow plugs for other applications (gm's continuous duty cycle perhaps) would be higher but this test works for mercedes, volkswagen, peugot, idi, powerstroke, and isuzu. Thats what I have tested so far.

Tim, where did you get the test you recommend? I have never heard of that (I do find it interesting though). I know the gps resistance changes under load and have always kinda wondered how to check it. I do wonder about the setup though. 12v / .3 ohms = 40 amps, which is above the limit of my dvom (internal fuse is 10 amp).

punk

Punk has the proper procedure outlined above. But make sure you disconnect the wire attached to each GP before you check resistance. Since they are connected in parallel you would be checking resistance thru multiple GPs if the wires weren't disconnected for the test.

Regards,