Hard Start, Glowplug Light Not Coming On - Testing
 

Had a hard start yesterday; knew something was going on with the glowplug system as the glow plug light on the dash wouldn't light up every time I turned the key.
I put a new fuse in cause I had one and they're cheap.
Then I searched here & read that the light won't work if there are two or more plugs not working. I pulled the harness plug from the glowplug controller on the driver's side fender wall just behind the headlight to test my plugs, connecting one probe of my multi-meter to the battery ground and the other to each of the five numbered ports. (I also checked voltage at the pins on the controller to be sure they were getting 12V when the key was at the #2 position - they were, so the controller is good)
Here's the readings I got:
1- 202
2- 0.8
3- 220
4- 0.8
5- 0
I will pick up three new Bosch plugs today at Autozone.
I am wondering why all three went bad all of a sudden as the car always fired immediately every cold start before yesterday :confused:

Doesn't bad things happen in threes?

Veg,

Are you sure you don't mean infinite resitance for #5 GP. Its almost impossible to get 0 ohms because there is always the contact resistance and resistance of the wires. If there was 0 ohms (short circuit) the fuse in the GP relay should melt and open the circuit.

To get 2 GP with readings of about 200 ohms is weird. Did you try connecting these 2 GP to the battery to determine if they glowed?

P E H

...........further supporting the case that a glow plug is not a light bulb. ;)

At work we don't do ohms tests on glow plugs. We just scratch a jumper from the battery to each plug (unplug the connecter of course) if it sparks..good injector, if no sparks...bad injecter. On my car the light would not come on after 2 glow plugs failed.
Not sure if it's my controller though but lately the glow plugs work great in the morning but after the car sits in the sun all day they won't work and the car cranks a bit before starting. I'll look into that another day.

_________________
83 300sd
3 Fords

Probably 3 didnt go bad at once. It just started ok with 1 bad, then 2 bad. The same thing happened to me 2 weeks ago. The part store I use only sold them in fours !! So my glow plugs are 80% replaced.

I think I need a new battery in my multi-meter... Changed out #1, new one tested at 0.9-1 ohm, checked the rest of them and #5 now magically tested 0.9-1. Anyway changed out #1 & #3, the dash light would come on now and this morning it fired right up. :)
Tested the two across the battery - they are definitely kaput.
In the archives I read one post that said the plugs should be ~0.8 ohms, another said they should be ~1.2. On my truck they were 1.2-1.6.
Anyway it works now, 0.8-1 ohm seems to be the number on these plugs.
I like BenQ's test.

Brian,

I thought the ~200 ohm readings were extraneous resistance readings. So I still say 99% of GP are like light bulbs: they burn out completely.

I did have one loop type GP that did short out to ground. That was the 1% that didn't go open like a burned out light bulb.

P E H