No voltage at glow plugs

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cwill
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No voltage at glow plugs

Postby cwill » Wed Mar 25, 2020 11:17 am

I've cleaned all the connections well. I've tested for continuity at the dropping resistor, fusible link, and the hot wire that goes to the bus bar. All passed. I have continuity at the two wires for the thermo switch, but there connection in the housing may be suspect. Both relay 1 and 2 click on almost simultaneously when the coolant temp. is cold. I think 1,closer to the front of the truck first, followed by 2. I haven't verified that the relays themselves work properly and I haven't checked continuity on the glow plugs. Those two things are next. Any other tests I am missing?
~Chris
82 Chevy Luv
2.2 Dsl
4spd & 4wd

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puttputtinpup
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Re: No voltage at glow plugs

Postby puttputtinpup » Wed Mar 25, 2020 12:22 pm

If one or more glow plugs are bad, the controller will cycle the 1st relay on, then off almost immediately. The clicking off may be what you're thinking is the 2nd relay coming on.

If you have a test light, you could clamp the one end to the bus bar the run a jumper from the point to ground. See if the light goes on then off quick when key is turned on.

There's one other place to chk. A plastic connector on the firewall that has a few wires going thru in. Clean it up hood. Also a bad ground near that corner firewall corner I think. I forget exactly where. This was recently posted by a member and found to be the culprit is his situation.

cwill
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Re: No voltage at glow plugs

Postby cwill » Wed Mar 25, 2020 2:26 pm

In your second paragraph, do you mean clamp the test light to the bus bar, then run an additional wire from that point on the bus bar to the negative terminal on the battery. Cycle the plugs and if the light goes on then off immediately this means what?
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puttputtinpup
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Re: No voltage at glow plugs

Postby puttputtinpup » Wed Mar 25, 2020 4:05 pm

cwill wrote:In your second paragraph, do you mean clamp the test light to the bus bar, then run an additional wire from that point on the bus bar to the negative terminal on the battery. Cycle the plugs and if the light goes on then off immediately this means what?

My circuit tester has a springy cord with a clamp on it that normally clamps to a ground. The tester is plastic with a bulb inside and a metal point. Basically I'm suggesting reverse the pos & neg by clamping cord to the bus bar, don't let it touch anything ground. The pointed end cram it somewhere into the NEGATIVE battery clamp so it stays put on a good known ground. Have a good view of the tester bulb from the cab. Turn key on and is light goes on a split sec and back off, in synch with relay clunck, it's likely one glow plug is bad.

cwill
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Re: No voltage at glow plugs

Postby cwill » Wed Mar 25, 2020 5:30 pm

I removed the busbar and tested each glow plug for continuity while still in the block and all four passed. I charged both relays one at a time at the small spade ends and tested for continuity across the big spade ends and both relays passed. I cleaned the ground connection on the passenger side inner fender. It seemed clean but I made it cleaner. I'm thinking the only thing left is the two wire thermo switch. Both wires broke years ago, and I crimped two eye ends on the end of each wire and put a screw through both of them through and into the resin. I'm thinking the screw may no longer be making good contact. Is there a test for this? The glow light does come on and cycle as it should.
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puttputtinpup
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Re: No voltage at glow plugs

Postby puttputtinpup » Thu Mar 26, 2020 12:31 am

Good. On the right track. The sensor in the thermostat housing I'm pretty sure is only to tell the controller if the engine is warm enough to not need glow plugs. It defaults to run the glow cycle if it thinks temp is cold. Either way, you can fix it. I usually dremel out some epoxy from around where the wires broke and expose some metal. Solder new wires on and attach to existing wires. The section of wire nearest the sensor will be dry & brittle. Cut that off. Fill in dremelled part w jb weld.

The heavy connectors at drop resistors and fusible link, etc may spread and be loose. I removed the spade and female end from the plug, cleaned em up and closed the female end up w plyers to bite the spade better.

cwill
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Re: No voltage at glow plugs

Postby cwill » Thu Mar 26, 2020 2:49 pm

Thanks, I've seen that method mentioned before on this forum as a fix and I will do that also. On the off chance that does not solve the issue, I'm thinking the QOS controller may be faulty. I doubt it, but I figure it is possible. Is there a good test for this controller?
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puttputtinpup
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Re: No voltage at glow plugs

Postby puttputtinpup » Thu Mar 26, 2020 3:22 pm

I'm not quite sure about an actual controller test. Before this forum began, I had issues with my white pup. Thinking the 1st relay was bad, I ran a Ford starter solenoid in its place and used a toggle switch to manually activate the glow plugs.

There are a couple of small wires at the rear of the bus bar (the curved flat metal.... measures the resistance?) and where the hot wire connects to the bar. Make sure they're attached.
Paul has more knowledge about how the controller works. I have a shortcut somewhere here about a problem component in the controller. I'll try to find it and post here.

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puttputtinpup
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Re: No voltage at glow plugs

Postby puttputtinpup » Thu Mar 26, 2020 5:49 pm


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puttputtinpup
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Re: No voltage at glow plugs

Postby puttputtinpup » Thu Mar 26, 2020 5:55 pm

This thread has a hand made schematic and a picture of the board. There's a component on the board that I'd read about years ago that was commonly found to be bad. I wanna say it's the r100 resistor circled bit not 100% sure
viewtopic.php?f=1&t=23913&p=154736#p154736

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Paul
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Re: No voltage at glow plugs

Postby Paul » Thu Mar 26, 2020 9:43 pm

cwill wrote: Both wires broke years ago, and I crimped two eye ends on the end of each wire and put a screw through both of them through and into the resin. I'm thinking the screw may no longer be making good contact. Is there a test for this? The glow light does come on and cycle as it should.


It's not clear to me exactly what you did here. So, I will point out that if the two thermo switch wires are connected together they will disable the glow controller. Might want to check for this. Also, the glow controller will be disabled if the yellow wire gets grounded by your screw.

Does the glow light actually stay on for 5-7 seconds? I cannot think of how this can happen if the glow plugs are not heating normally.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

cwill
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Re: No voltage at glow plugs

Postby cwill » Thu Mar 26, 2020 10:25 pm

Sorry, I misspoke. Of the two wires on the thermo switch, the wire on the driver's side broke and that is the one that had an eye crimp put on the end of it and a screw put through it into the resin. It worked for years until recently. The passenger side wire broke after I was having GP problems. I did the same fix and put the two together in the resin. The QOS controller though, did not seem disabled because I could here it clicking. That makes me think that the screw was no longer in contact with anything electrically functional. I'll make the proper repair then report back. Thanks,
~Chris

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Paul
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Re: No voltage at glow plugs

Postby Paul » Thu Mar 26, 2020 11:31 pm

cwill wrote:Sorry, I misspoke. Of the two wires on the thermo switch, the wire on the driver's side broke and that is the one that had an eye crimp put on the end of it and a screw put through it into the resin. It worked for years until recently. The passenger side wire broke after I was having GP problems. I did the same fix and put the two together in the resin. The QOS controller though, did not seem disabled because I could here it clicking. That makes me think that the screw was no longer in contact with anything electrically functional. I'll make the proper repair then report back. Thanks,
~Chris

Actually, I misspoke too. The sensor with two wires are for the idle speed step up. The glow controller disable sensor has just one yellow wire that gets grounded (with a hot engine) by the switch in the sensor.

You can disconnect the yellow wire from the sensor to see if that is disabling the controller.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

cwill
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Re: No voltage at glow plugs

Postby cwill » Fri Mar 27, 2020 4:57 pm

I soldered both wires to the two wire thermo switch. Since the switch was removed, I tested it like the manual says by putting it in water, slowly raising the temperature, and then checking for continuity. The manual more or less says the switch is on when the temp. is 50'C or lower and turns off when it's above 50'C. I checked continuity on the sensor body hot and cold and it passed both times. I checked continuity at the terminal ends, hot and cold, and it failed both times.Finally, according to the manual, I checked continuity from each spade of the terminal to the body of the sensor,hot and cold, and it failed all four times. If the switch is on when it's cold, I figured there would be continuity, and then as the temp. rose, continuity would be broken and the switch is turned off. I feel like I'm in the market for a new two wire thermo switch. Am I missing something?
~Chris
82 Chevy Luv
2.2 Dsl
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puttputtinpup
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Re: No voltage at glow plugs

Postby puttputtinpup » Fri Mar 27, 2020 6:16 pm

That 2-wire switch, as Paul indicated, is for the fast idle circuit. It throws 12v to the little black vacuum switch on the left fender near the baffle box that routes vacuum to the fast idle servo at the back of the injection pump.

The single wire sensor is for the glow plugs.