Glow Plug Test?

[HammerDown]

Hey fellas, refresh my memory on how to test a used GP with the resistance method.
I have an older BluePoint digital multimeter; where to put the meter leads and Meter-settings and what resistance number to look for.

Reason...I can tell from a dead-cold start I know I have one bad GP but, I have several used GP's that were 'good' when I replaced all-8 Motorcraft/Beru's 3 years ago.

*Not wanting to replace all 8 of them again $$$$ and would rather try one of my 'good' used GP's in the bad hole and would like to test the used batch for the better used GP. I also don't want to put one NEW GP in with the older 7.

(I usually test while in the engine with a test light) light on = ok, no light = burned out and in the trash it goes.
Thanks, Ray

 

[homelessduck]

I pull them out and hook them up to jumper cables.

 

[BeastMaster]

Personally, I like an old tester for this kind of thing I made from a tail light bulb and holder... a length of wire and alligator clips. The purpose of the light bulb is to draw SOME current, and show by incandescence that current IS flowing. I found this little device quite useful in troubleshooting 12V power circuits, a bad connection would often give itself away by dimming. Choose about a 1 to 2 ampere bulb. I used a 1156. They draw 2 amperes. The Dollar store around here had 'em.. two for a buck. The sockets, I had scrounged from some scrap. If you are desperate, its possible to solder the wires directly onto the bulb base. Use tape to insulate. But if you do this, don't use your test lamp for illumination long enough for it to heat enough to melt your tape.

https://www.rvledbulbs.com/v/vspfil...eets/performancechart12vincandescentbulbs.pdf

On the installed GP, remove the top connection wire. Place your bulb connections between the top connection of the GP and the truck battery positive. Grounding the other end of your test lead should bring the bulb to full brightness.

A good glow plug should be near a dead short, and the bulb should glow with nearly the same brightness as it did when you grounded it. The light bulb will prevent you messing up your glow plug by limiting the test current. Check each of em... they all oughta look identical by brightness. Check your spares too while you have 'em out. Hold the body against a ground bolt somewhere and touch your test lamp to the connector, so you are routing the current through your GP.

The only reason for removing the wire from the top the GP is to prevent the other GP's on the circuit from taking your test current and giving you a misleading reading. At least you do not have to remove the plug to test it. The engine provides the ground return circuit.

Once you have made your little tester, you may find it to be one of the handiest little quickie troubleshooters for tracing other faults in your power distribution circuits as well. If you break or lose it, oh well, its easy enough to make another. Things like this are a good use for those combination brake light/tail light bulbs when only one filament went. I have given more of these things away to my friends when I catch them troubleshooting their wiring, as the dollar store was also selling bags of clips for a buck, and I got so much wire out of an old washing machine that I have enough snippets of wire to last me a long long time.

 

[BeastMaster]

Oh yes, the resistance on a good GP is so low its hard to get a good reading without your test leads and connections messing you up. Homelessduck has a good way as well, power em up and see if they glow. Otherwise, look for a spark to indicate current is flowing. But don't hold it there too long .

 

[snicklas]

Ray,

With a DVOM, set it on ohms, if not an auto-ranging meter (I have a Fluke, and it only has VAC, VDC, Ohms because it auto-ranges) put it on the lowest setting. Put one lead on the hex and pull the bullet connector off the glow plug and touch the other lead to the bullet (the circuit path is bullet connector through the tip and out the threads/hex). A good plug should be only a few ohms when cold, something like 3-8 ohms. If you get 0 (a dead short) or you get meg-ohms or infinite or an open type response (my meter says O L) if there is an Open Loop because the plug is burned "open". So, a few ohms = good, 0 or infinite = bad. My guess is you will find a high resistance on one, a short would draw current and the controller would see that, and cycle more "normally" than an open, which is less current, which causes the short cycle and the quick after-glow clicking......

Or, if you have a 12 volt test light:

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Connect the clip lead to the positive battery post. Unhook the bullet connector and touch the tip to the bullet. If the bulb lights, more than likely the glow plug is good (unless it is a rare shorted plug). If the light doesn't light, the plug is bad (burned open). I have used this method and found bad plugs, that were confirmed after removal by ohm-ing them out, and they were either in the meg-ohm range or OL (open).

You may also find that just messing with the connectors they all start working. Might have a marginal connection, and just unhooking and re-connecting them gets everything cleaned up and working again.

 

[HammerDown]

I pull them out and hook them up to jumper cables.

Actually way back when I purchased my truck 'new'...and I would replace the GP's I would 'burn' the old ones out of the truck via 12v battery and two wires.
I would indeed notice 'some' lighting faster and hotter than others.
I just wanted to go through my bag of 'used' GP's and try the resistance test with a multi meter I have read some do...but not sure of how to do it.

 

[snicklas]

Actually way back when I purchased my truck 'new'...and I would replace the GP's I would 'burn' the old ones out of the truck via 12v battery and two wires.
I would indeed notice 'some' lighting faster and hotter than others.
I just wanted to go through my bag of 'used' GP's and try the resistance test with a multi meter I have read some do...but not sure of how to do it.

Ray,

To test them out of the truck, put one lead on the hex or threads, and the other on the bullet connector. A good plug should read just a few ohms, at least 2 or 3 ohms, but not much more than 10 ohms or so. That is what I found testing known good ones. Again, 0 ohms is bad because it's shorted, and meg-ohms or infinite resistance is also bad, since that is open. Using the above is how I tested several, and when the ones that tested good (just a few ohms) were put back in the truck, they worked.

 

[HammerDown]

Ray,

To test them out of the truck, put one lead on the hex or threads, and the other on the bullet connector. A good plug should read just a few ohms, at least 2 or 3 ohms, but not much more than 10 ohms or so. That is what I found testing known good ones. Again, 0 ohms is bad because it's shorted, and meg-ohms or infinite resistance is also bad, since that is open. Using the above is how I tested several, and when the ones that tested good (just a few ohms) were put back in the truck, they worked.

^^^ exactly what I did...and all my old used Beru's showed the same resistance as one 'new' never used GP.
As I mentioned prior, this time I don't want to spend $$$ on a full new set of GP's and I don't want to put a 'new' GP in with the old.
If I had a few that were dead then yes, I would replace them all. But for one or maybe two possibly three, I'd rather use-up a few 'good used' GP's that may have some significant life to them.

 

[HammerDown]

Interesting as almost 90% of the time when a GP fails it is the rear drivers side.
Also, has anyone else notice the Motorcraft/Beru ZD-9 GP's erode away at the bottom 1/4" ?
I installed a good old ZD-9 GP.

BTW, all new ZD-9's were installed in late 2013 (still have the receipt)

 

[Macrobb]

I test mine in the engine with a piece of 10ga wire to B+. A good glow plug produces nice sparks as you touch the terminal. A bad one produces really weak or no spark(usually no spark).
Very easy and can be done without removal.

 

[u2slow]

I use a DC clamp-on ammeter.