glow plug controller

[toytec]

im just wondering if it is possible for bad glow plugs to take out the glow plug controller? i have never heard of this but a ford guy told me that. i've always thought that a bad controller will take out the glow plugs but not vice versa. anyone clear this up for me?
also whats the resistance spec for the glow plugs? mine are all around .8 of an ohm which i think is fine, but what is the max? and is there a min, can u have too little resistance in a glow plug? i don;t believe so but this guy seemed to think so.
thanks

[BuilderBob]

i've always thought that a bad controller will take out the glow plugs but not vice versa.


A bad controller will allow the GP's to remain "ON" for too long and cause them to burn "Open".


also whats the resistance spec for the glow plugs?

No one has published exact ohmages for GP's, follow this advice,
Open = Bad
Continuity = Good
Ford, in the manual, recommends test with a test light, not a meter. Remember
Open = Bad
Continuity = Good

and is there a min, can u have too little resistance in a glow plug?

Well yes & no, if the resistance go down, then current goes up, too much current will cause too much heat, and the GP will burn OPEN, all of this happens in milli seconds.

The GP circuit is protected by fuses, better described as "fusible links"

If you currently have 8 open GP's, I would suspect a bad controller (rare).
If you have 1 or 2 bad GP's, I would suspect old GP's. Remember nothing last forever.

No matter what you must have 8 good GP's for the the system to work correctly

[cdnsarguy]

This info is from a Ford expert.........

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.
DieselDon