How much resistenance should a good glow plug have. the truck is a 89, F250, with a 7.3 IDI.

My "wait" light use to be on for 15-20 seconds and now is only on for 5+- and it is a bear to start wihout a little either

 

i'm going to make a suggestion. DON'T USE EITHER!!!!! Using either in these engines is like throwing a gernade in you cylinders. A normal 7.3idi from what i read on here is like a21:1 compression and using either can really raise havok on everything. don't know what resistence is supposed to be. I need to check mine. I think my controller works alright but i think i may have a couple bad glows. Seems that when it's cold it takes a few turns to get it to fire. Once it's warm it fires right off.

 

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

 

all 8 glow plugs on my 88 tested good with the test light, and ohm meter this spring.
when i pulled them, i tested them all with straight 12 volts. only one lit up, and that one only lit 1/2 of the plug.
so you can not entirely trust the test light or ohm meter either.
at a cost of only $9.99 each, if in doubt, i replace them.

 

If one is going bad - then replace as a set. Just like spark plugs. Why take a chance of not starting some cold day at work with nobody left there to give you a lift.

 

PLC - What black wire to the valve cover. Where does it source from.


Thanks
Ken

 

Black wire labeled ground.
The silver end of the black wire is a ring terminal side view, I did not notice it was turned the wrong way when I took the picture.
On some trucks it was installed on the mounting bolt for the controller in the rear center of the intake manifold.