Glow Plug question

BHarrison · Mar 19, 2002

Hello All. I just bought an old toyota diesel pick, and the glow plugs are not working. Well, I can replace them easy enough. One thing I find myself asking is, how do you know when one goes out? It's pretty obvious when 3 or 4 go out, (on a 4cyl)
but how do you tell if you lose 1 or 2?
I guess you could measure total current, but I don't have anything that measures 80 amps!

Thanks

HalseyGreen · Mar 19, 2002

Here's how I check the glow plugs on my F350 - I have a wire with alligator clips on both ends, attach one to the positive terminal of the battery and they touch the other end to the glow plug, if I get a spark I know the plug is working somewhat, if not spark, then I know its open and should be replaced. On the Ford, the glow plug controller depends upon the resistance in the glow plugs to function correctly. If a glow plug goes, you notice the controller cycling faster then if all are working. Don't know about the Toyota. Hope this helps.

BHarrison · Mar 19, 2002

There is a controller, and some sort of resistance measurement happening. The glow plugs have power for about 90-120 seconds after the key is first turned on. I have ordered the OEM service manual, and will learn more when I get it, but I'd like to attack the glow plug issue promptly.

Will it hurt the engine spinning over without the glow plugs on?

cowboydoc · Mar 19, 2002

Ben,
You can check them just like Halsey said. Also it won't hurt to turn it over without the glow plugs on.

BHarrison · Mar 19, 2002

Is there a way to tell if you have one out while it's still in the engine?
What's the first indication that one is out?

Anonymous Poster · Mar 19, 2002

<font color=blue>...Is there a way to tell if you have one out while it's still in the engine?...</font color=blue>

Simply disconnect the B+ lead going to each individual glow plug terminal and ohm it out from that terminal to ground. {Warning... Not all glow plugs operate on 12volts... some operate much less (the controller pulses the B+)... so it's not advisable to "just hook up 12 volts and test for smoke...?"}

A good glow plug will read ~~1-3 ohms {or a very low resistance}. A bad glow plug will read open or infinity. A glow plug is nothing more than a "miniature heating element" with a controlled "on" time.

While the B+ wire is off you can check for voltage at that plug with the switch on.

Hard starting is one indication a glow plug or a few are out...

TWINKLE_TOES · Mar 19, 2002

Ben,

If you have a voltmeter capable of measuring millivolts, you can measure the drop in the wire to the plug when the glow plug is on. At ~10-15 amps/plug you should be able to see a few 10's of millivolts for a plug that is operative, zero if it's not.

Al