Went to start the old blue beast this morning and found the glowplugs to be out again and of course i had no cosby juice since it started percect since the new gp. i just recently bought motor craft ones from oreilleys worked great till now nothing. They dont even pull amprage usually you could tell it was working. Any how..... any ideas on why it ate a set of gp so fast? also its on a manual switch never run longer than 10sec since installed
Ate 2 sets of gps in a month or so
- Thread starter Azidiguy
- Start date
Austin86250
Full Access Member
did you use ether plus glow plugs? it can blow them up
also really advanced timing can cause loss of glow plugs
also really advanced timing can cause loss of glow plugs
Nope no either with plugs only once they failed. I dont currently have timing equip any symptoms of advanced timing? It seems to run pretty good does smoke though
Manual on a button
SkylabTech86IDI
Full Access Member
A shot in the dark here but Is there any chance of the manual button having loose internals causing the plugs to intermittently come on while running? Swapping to a new toggle button could help isolate the problem.
Could be ill look into it
Or is it possible the switch or something has failed and they're not getting power? I've been there before.
Not likeley as the gp relay audibly clicks and shows its passing voltage on a meter
IDIDIDIhoDhoDhoDO
Registered User
Did this problem start about the time you wired in a manual switch? Is the system still original otherwise?
Had the switch since its been running truck is a 460 to odi conversion. No idea how it was set up before.
gnathv
Full Access Member
It could still be your relay. You can have volts but no current. Put one lead on the power lug and the other on the load lug and see if you’re dropping any voltage across the relay contacts. If no voltage drop, check resistance on a couple of glow plugs.
IDIDIDIhoDhoDhoDO
Registered User
The first thing I'd eliminate is if the glow plugs are being over-volted. At the relay/controller unit there is a wavy Z-shaped shunt resistor that connects the outlet post of the relay to a post on the controller. The end of that resistor at the controller post is where the wiring harness for the glow plugs themselves takes power. You'll need a new set of functioning glow plugs but once they are installed then connect the + of a DC voltmeter to that post (the bottom connection of the Z-shaped shunt resistor) and the - to a good ground on the motor and then hit the glow plug switch.
You should see the voltage start at around 8 or 9 and go up in a few seconds to around 10. It should creep up to maybe 10.5 by the end of your 10 second cycle. If the voltage goes higher than this, to say 11 or higher, then you are likely over-volting the plugs.
Also, if the shunt resistor is missing and someone simply connected the glow plug harness straight to the output terminal of the relay it could also cause this.
Are all your glow plugs reading infinite resistance or just a few of them?
You should see the voltage start at around 8 or 9 and go up in a few seconds to around 10. It should creep up to maybe 10.5 by the end of your 10 second cycle. If the voltage goes higher than this, to say 11 or higher, then you are likely over-volting the plugs.
Also, if the shunt resistor is missing and someone simply connected the glow plug harness straight to the output terminal of the relay it could also cause this.
Are all your glow plugs reading infinite resistance or just a few of them?
Was this the case even on a 6.9? I know my 7.3 had the wavy thing. Will test resistance in the morning when i get back to the truck. I also have a new in box gp relay ill put in for good measure.
IDIDIDIhoDhoDhoDO
Registered User
That I don't know. I've never worked on a 6.9, but the 6.9 and 7.3 use different glow plugs.
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