On my 87 e350, I'm having a heck of a time figuring out why my glow plugs aren't working right. On a cold start, I get about 4 seconds of the wts light, and usually have to run the plugs twice to get it to start. Sounds like bad plugs, sure, but they all passed a test with a test light, and since my multimeter had bad leads I couldn't test resistance with it, so I hooked up each plug individually to a battery charger for a couple seconds, and all of them pinned the ammeter of the battery charger to its 15a limit, maybe more.
I've previously upgraded the wire supplying battery power to the glow plug relay, it's now a 4ga wire the whole way. Relay looks ok. I've also tested for power to all 8 glow plugs and they all get power.

So I'm not sure where to go from here, any suggestions better than blindly throwing parts at it till I get lucky?

 

Disclaimer: I'm an electrical engineer, not a gear head, and never designed stuff for similar applications....so my knowledge may be a bit off what guys with more practical experience would tell you....believe them if we disagree.

My new glow plugs all measured around 0.1 ohm on my meter....ohm's law sez that should suck 120A from a 12V battery. Ohm's law also sez that 15A at your charger would mean 0.8 ohm resistance, which sounds high to me, although it would acceptable from what I've read.

I don't think that the actual current for one glow plug would be 120A....but I expect it would be more than 15A, so that test may not be enough to show one operating marginally.

My glow plugs had mostly failed (3 with 0.1~0.2 ohm; 5 effectively open, kohm or megohm resistance), and my WTS light went out immediately....and the van didn't want to start. New ones fixed all that. And I realized that they had been slowly dying over the years, and it had been getting harder to start....and I had been using the block heater more and more....until it was completely failed.

I believe that the WTS circuit confuses failed (high resistance) glow plugs with resistance increasing due to actual heating, and turns them off earlier and earlier as more glow plugs go bad.

Does it start better if you use the block heater?

 

i never check glow plugs with ohm meter, i have seen way too many "test good" but not light.
if glow plugs are questionable, i replace them for the simple peace of mind that they are new.
the proper motorcraft glow plugs are under $10 each at rock auto.

 

I'd be looking at the controller at this point. Your charger test is 'good enough'; note that as a GP warms up, it's resistance changes(increases when temperature increases).

This is also how the controller senses the temperature increase, btw - by looking at the current draw, which is determined by the resistance.

One idea - make sure that the relay on the controller isn't creating a bit of resistance itself - get a working voltmeter, and put it across the big terminals of the relay while someone turns the key on. With the relay off, you should see a full 12V across it(the ground being provided by the glow plugs). With the relay on, that should drop to almost 0. 0.3v or something is good, 1v+ is bad.
I had a relay like that once; probably corroded contacts internally.

 

I have never seen one that passed the test light test not work. Only been at this for 55 years.

 

Good to hear from you, thought we lost you after all this time.

If you have some wire and a momentary switch you can hook them up to manual activation and run them as long as you like that way. (I've had mine manual for about 5 years)
It's also a killer test to eliminate the controller. If the van doesn't start with the switch then you've eliminated that as an option. And vice versa, if it fires right up then it's the controller that's bad.

The short version is: replace the white wire on the relay with the wire that goes to your switch, which must be grounded. Done!

Just make sure it's a momentary switch, if you bump a rocker they can burn out or maybe worse...

 

Thanks for all the input guys! I'll be testing the relay this weekend and see where that leaves me.
I'll post back with an update in a couple days.

And to clarify from the original post, it's not that my plugs pulled exactly 15a each, it's that my battery charger gage only has a capacity of 15a, and was pinned to its limit testing each one.

 

Ok, I finally got some answers here. I believe The controller itself has failed.
I tested the relay and found a voltage drop of only 0.1v across it, so thats good. I also tested the supply wire to the relay by comparing the voltage at the relay against battery voltage under load, and only lost 0.4v
However, while testing, I noticed that my relay clicks on, stays on for a couple seconds more than the wts light, maybe 6 or 7 seconds total, then clicks 3 or 4 times quickly, then stays off, not cycling like it should. That's what indicated to me that the controller failed.

I realize I can save a few bucks by running them on a push button instead of the controller, but I'm thinking of keeping it with the stock style controller. Bwd is the only brand listed at oreilly's, and they're generally respectable, but has anyone here used one and can attest to the quality?

 

BWD is not acceptable. Motorcraft/Navistar/Beru only.
I long ago gave up on meter or test light testing glows. I pull each one and power it up with booster cables. Then you know what is happening.

 

I already know that for the plugs themselves, it's Motorcraft only, but it's good to know that about the controller as well. Last night I wired up a pushbutton to the relay, but left the controller connected as well, simply adding a wire to the control terminal. I found it interesting this morning that as I held my pushbutton for ten seconds, the wts light stayed on for about 5 seconds, then went off, but my engine started easily. I don't really understand that, but it seems to work well, I just don't understand the light.

 

that is why i do not trust the in-dash light and run my own glow plug light off the output terminal of the glow plug relay.

 

I'm back to feeling confused on this one. Tonight I went to start it after work, held the button down for ten seconds, light stayed on 4 seconds, went to start and it was like my plugs weren't working. Took a couple more tries to get it going. I must be missing something

 

drop from R or M almost to bottom, two needle widths to the left of N [ of NORMAL ].
I can see that the controller holds the g.p.'s on for 20 seconds typically.
Twice what you are doing at 10 seconds. You should hold your override button on for 20 seconds, not 10. I sometimes do two g.p. cycles before cranking, for extra heat when needed.

This uses the dash volt meter as an indicator of "GP's ON". They aren't on unless the voltage has dropped significantly, like from 12 to 9.

At night I also use the cabin light the same way.
1. Key off, cabin light on, the light is bright.
2. As soon as I switch to RUN, the gp.s come on, voltage drops to 9, and the cabin light dims noticeably.
3. I just wait for the light to go bright to know that the g.p.s are off/done and its time to crank.

You should confirm that while the button is held, the voltmeter is to the left of N, or the cabin light is dim.

 

light in the dash, or a light you added?

 

The light in the dash is the only light I'm focused on here