GP's or Controller???

[coletrain777]

Quick question,
I know I could search, but I am just too tired tonight and I need a fairly quick answer so I can order what I need tomorrow. My 94 IDI either has a bad GP controller or GP's but I don't know which. The WTS light is only staying on about 4 seconds at the most, and if you turn the key off and back on the light goes immediately off (doesn't stay on at all). It also clicks after it turns off. Do you guys think this is the controller or the GP's. I don't really have time to test the GP's so I was just wondering about your guys thoughts.

 

[NCheek]

On the solid state controller, glow time is controlled by plug resistance. Bad plugs lengthen glow, bad ground makes glow shorter, the combination of the two results in a bad start but seemingly normal glow times.

It's probably plugs, but you should look into your problem more before you just throw parts at it.

 

[coletrain777]

so it could be bad plugs even though the cycle is shorter rather than longer. Didn't you say that bad plugs lengthen the cycle ??? Not trying to sound smart (my previous sentence looks like I am being a jerk to me), just trying to understand. I always thought that the cycle with the WTS light would be shorter if you had bad plugs. If it's just bad GP's I already have a set of ZD-9's sitting on the shelf. I guess I need to ohm them huh?

 

[Metalmacguyver]

What is considered a normal or good glow time?

 

[NCheek]

Coletrain: I would say go ahead and ohm them, and check all your GP related connections just for good measure.

Macguyver: Normal glow for a 7.3 which has the solid state glow system will normally be about 8-10 seconds unless it is really cold. It will also do some shorter, one second bursts known as "after-glowing" once the engine is running to reduce white smoke and aid warm-up.

 

[Agnem]

Ncheek has the right idea, but said it awkward. Anything that increases the resistance will result in a shorter glow time. So a bad ground, or bad plugs will short cycle the contactor. When voltage is first applied to the plugs, you should see about 6 or 7 volts at the #2 glow plug location, measured with the glow plug attached. As the on time lengthens, the voltage will climb until nearly battery voltage at which time the controller will begin to cycle. So if you measure the voltage and see like 10 volts right away, it's going to short cycle and you've got bad plugs for sure. With a bad ground, the voltage will start out low as usual, but the controller will cycle anyway. That's a good way to tell which is the problem.

 

[NCheek]

I should have added a disclaimer stating that I am by no means an expert on the 7.3 system, but it seems like I had heard it described that way before with bad plugs shortening time and bad ground extending it?

 

[Agnem]

From an electrical perspective, since the electronics sense the current draw of the glow plugs with ground as the reference point, introducing additional resistance in the ground path will result in the circuit seeing that restance added in the current draw path. More resistance = less current flow, so short cycling should result from either event. In fact one of the most attractive features of the 7.3 system, is that any failure mode seems to result in NO glow plug voltage, where as the 6.9 system could fail and leave them turned on permanently.