Disabling Glow Plugs
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Mountain Pass
Joined: Mar 2004
Posts: 102
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From: Wilmington, NC
Disabling Glow Plugs
To disable the glow plugs for purging air out of the fuel system, which wire is the ignition to relay that needs to be unhooked? Thank you. All plugs reading about .6 ohms. Replacement time?
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
No need to disconnect/disable GPs for fuel purging... they will just cycle as normal with no harm. If you do not want the start then disconnect the FSS on the IP.
If you have 2 or more bad GPs, the controller may not cycle at all.
Two problems that occur with the solid state ( 1987 to 1994 IDI engines ) GP systems. If a GP burns out ( circuit resistance goes up ), the controller cycles the GPs at a faster rate which doesn't let them get to max operating temp. If 2 or more GPs fail, the controller may not cycle the GPs at all ( very rapid or no clicking heard ). When you check the GPs, use an ohmmeter. A high resistance ( not necessarily burned out ) GP can cause circuit resistance to go up and the controller will then cycle the GPs too fast. You probably will not find this problem with a test light. Resistance spec for GPs = .5 to 1 ohm cold. Second problem. A poor controller ground ( black wire attached to valve cover stud ) will cause the controller to leave the GPs on longer, often damaging or failing them. If you are having mulitple GP failures, I would check closely the controller ground. Now the confusing part. Bad ground --> longer GP on time ( slower cycling ). Burned out GPs --> faster cycling If you have both situations, it may appear that the controller is cycling the GPs at the proper rate. Bad ground slows it up while the burned GPs speed it up ---> normal cycling. The system acts/sounds like it's working normally, but you have a hard starting concern.
By........DieselDon
Glow plug torque is 12 ft lbs, I always use antisieze on the threads.
If you fellas put up truck info we could help you find things...
If you have 2 or more bad GPs, the controller may not cycle at all.
Two problems that occur with the solid state ( 1987 to 1994 IDI engines ) GP systems. If a GP burns out ( circuit resistance goes up ), the controller cycles the GPs at a faster rate which doesn't let them get to max operating temp. If 2 or more GPs fail, the controller may not cycle the GPs at all ( very rapid or no clicking heard ). When you check the GPs, use an ohmmeter. A high resistance ( not necessarily burned out ) GP can cause circuit resistance to go up and the controller will then cycle the GPs too fast. You probably will not find this problem with a test light. Resistance spec for GPs = .5 to 1 ohm cold. Second problem. A poor controller ground ( black wire attached to valve cover stud ) will cause the controller to leave the GPs on longer, often damaging or failing them. If you are having mulitple GP failures, I would check closely the controller ground. Now the confusing part. Bad ground --> longer GP on time ( slower cycling ). Burned out GPs --> faster cycling If you have both situations, it may appear that the controller is cycling the GPs at the proper rate. Bad ground slows it up while the burned GPs speed it up ---> normal cycling. The system acts/sounds like it's working normally, but you have a hard starting concern.
By........DieselDon
Glow plug torque is 12 ft lbs, I always use antisieze on the threads.
If you fellas put up truck info we could help you find things...
Last edited by PLC7.3; Nov 20, 2007 at 10:28 AM.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
At .6 ohms the power the glow plug draws is 20 amps.
That is 4 amps lower than what they would draw at .5 ohms.
The higher the resistance, the lower the current draw gets.
Remove the connectors from all the glow plugs, but try to not disturb the harness much.
Now see what you have for an ohm reading on the harness.
There must be a short somewhere.
That is 4 amps lower than what they would draw at .5 ohms.
The higher the resistance, the lower the current draw gets.
Remove the connectors from all the glow plugs, but try to not disturb the harness much.
Now see what you have for an ohm reading on the harness.
There must be a short somewhere.
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