Glow plugs
 

The relay can drive you crazy...That thing uses a magnetic reed switch and a comparator circuit to try to tell the driver something...inside it senses the current through GP#1 and the total current through GP's 2 through 5 as they are all tied together inside the relay/timer to switch the lamp on or off independent of whether the plugs are glowing or not...It is an over-complicated device that confuses more than it helps....most of the time it has the problem and the driver is going insane trying to figure out what it is doing.....It is trying to do too many things with just a lamp indication....It is easier to learn Morse Code than it is to unwrap the mysteries of the glow plug lamp...I am going to put ammeter shunts on the plugs with bar graphs just for fun....Like the previous post says...I have changed my GP'S around so much...they just jump in there when I whistle...I would ream the prechamber if I had a reamer but have not had any problem with either the old series or newer parallel type with installation or removal...somewhere there is a post about using an allen wrench as a homemade reamer....Just a hint...sometimes it helps to tighten the plugs just a wee bit before backing them out all the way.....work them back and forth some as you remove them just to keep the threads from packing if they have been in there a while...

Glow plugs
 

Almost forgot.....Yes you can bench test them in a vise but I just let mine hang on the feed wires still in place with the tips in the air and the shells of the plugs grounded with jump wires....(parallel plugs only)....Series plugs just ground last plug...
This way you are looking at the plugs as they are actually being heated with the cars glow system and wiring....more of a (real Time) test.....
I just let them get hot enough to see how they are doing and then (shut them off)...
I have heard that running them for long times in the air could overheat the plug because you do not have the heat sink of the head as in normal installed use....I do not know this to be true ...but it sounds like it could be...so I stop them after a good visual check....no problems so far.....

I don't even put them in a vice. I grab a set of jumper cables and just hold on to the plug with them.

Scott

My experience tells me that GP's may fail intermittently, meaning you cna ohm them out, but after they start to heat up they open. My car went through a period where she ate GP's. I replaced the one's I had with store bought Motor craft GP's which really suck. Thank God the Ford plugs have a 2 year warranty. I also believe that when a GP fails, the others are stressed more (higher voltage due to the remaining GP's which shortens their lives)

Replace the one that's burned out to buy you time. Then replace all of them , saving the old ones for a cold rainy day.

Well, looks like I might have to play the plug pulling game this weekend then, I have 4 spares from my old engine, one original MB (has the star on it) and 3 fairly clean and fresh looking bosch. This will be interesting to see how it turns out. Of course, this will be if I have time after the tractor gets fixed, had that one apart for 2 yrs now :eek: , FINALLY got past the hurdle I've been beating my head on (with help from cold weather), got all the remaining parts I needed today, so this weekend it's on! I'm bound and determined to get that spot on my shop floor back so I dont have to grade the driveway by hand anymore....and get my better half to stop reminding me daily of it...:D
...All I wanted to do to it was fix the brakes....then the trans went out...DOH!

Great Idea. Save a lot of headaches. I recently replaced 2 glowplugs, and two weeks later, both dead. I have since replaced with "BOSCH" no aftermarket for me anymore. But will be nice to know if all areworking without having to test "once a week":idea2:

my glow plug system "sticks" on too, then it will blink. she starts up fine, the glow plugs will shut off when the engine has started, but when glowed the light goes out, the plugs stay on for a minute or so, then shut off. they all work. does this indicate a failed temperature sensor to tell the plugs how long to stay on. im talking about a 1980 240D by the way, so there are 2 sensor looking things between plugs one and two and plugs two and three. should those be checked?

as I understand it, it seems to be a perfectly operational system.

the relay will get a signal from the ignition switch when you start the car(search violet wire mod) which will then shut off the plugs. if you do not start the car, the plugs stay on, but the "wait to start "light will go off sooner or later, depending on temps.

your right on the the 2 sensors- one is for the gauge on the dash, the other for the GP system.