Yet Another Glow Plug Issue

[steelheadguy]

My truck has always had glow plug issues. When I bought the truck the plugs were bad. Ive now put 2 fresh sets of Beru plugs in and they just burn out within a couple weeks. I thought my first set went bad because of the controller cycling sporadically while I was driving.

This time Im puzzled as to why they have burned out. I have a momentary switch wire to the relay, and the controller not connected at all. 8 fresh plugs with 2 fresh batteries. The last time I took the bad ones out I tested the resistance of the plugs and non would give a reading, I tested them next to the new ones, all the new ones gave good readings.

The first week I installed the new plugs they worked fine. I also noticed a hum under the hood while they were glowing. Something I never heard before.... My last start with them I heard no hum and could tell only a couple worked because the truck stumbled to start. Now, no matter how long I glow, no start.

My only guess is to replace the glowplug harness and all wires. Figured Id ask here for any help and insight. Should I upgrade to the 7.3 harness? Thanks guys!

 

[79jasper]

I would look at the relay first.

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[Thewespaul]

Yep, and double check your wiring to make sure it’s not shorting and causing the relay to trigger while driving

 

[TahoeTom]

Look at the GP harness plug between engine and chassis. The two large orange wires (maybe yellow) carry lots of load and the plug tends to melt or corrode and the plug is a weak link.

 

[franklin2]

How long are you holding the button down to glow the plugs?

 

[steelheadguy]

How long are you holding the button down to glow the plugs?

Usually it only would take about 8 seconds. I tried 15-20 seconds and still nothing.

The relay still clicks on and off, is there a way to test if it is good or bad?

 

[franklin2]

15 to 20 seconds is too long, that could burn them up.

I am not sure you have a older truck, but do you have any type of voltage gauge on it? Mine is a 89 and came stock with a volt gauge in the dash. When the plugs are working, that gauge will go down to about 8 volts. When all 8 plugs are working they really pull the system down, I guess that is one of the reasons for two batteries.

If you could somehow tie a meter to one of the glowplug wires, and hook the other lead to ground, you could monitor the actual voltage getting to the plug harness.

 

[steelheadguy]

I would look at the relay first.

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Can a bad relay burn out the plugs? or would it just not glow them?

I pulled one plug out so far and resistance says 10 ohms. Thats a bad plug.

 

[79jasper]

Could do either.

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[steelheadguy]

Duh. Could get stuck on...
I cant think when Im worried about the truck. I dont know what Id do without this forum and all it's members.

 

[gerlbaum]

All I can say is I've been through every glow plug problem. Finally I 1) fixed the connection as.notrd above 2) built a new glow plug harness (to spec, don't over size wires if using 6v plugs) using 6.0 harness 3) new relay 4) push button. Fixed everything. It really is amazing how easy it is to start when it's cold and a proper working system. I really thought it was just a myth. Spend a weekend building a new harness (or if you're lucky buy one), new relay, and new glow plugs. That one weekend will save you headaches down the road, and time.

 

[steelheadguy]

OK the new relay is in. Im about to put the new plugs in and test the harness before the first cycle.

OK so now I have fresh batteries connected to the fresh relay.
The relay is operated by my momentary switch.
Two wires connected to 4 motorcraft glow plugs each.
This seems to be the most simple glow plug setup our trucks can have, what can go wrong?

The only kicker is.... I have a fuel line heater just before the fuel filter. It is wired off of the glow plug harness. What problems can this cause? I will test the resistance.

 

[79jasper]

Just unhook it. Not like it works anyways. Lol

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