85-93 Glow Plug Controller Modification

[ElGracho]

I'm having the warm start issues that many people have mentioned here in the past. I have new batteries, new starter, a good glow plug controller and new AC-60G glow plugs. When my truck (86 1/2 ton GMC with C code 6.2) is cold it starts fine. When it's hot it starts fine. When it sits for 30 minutes to 3 hours, it needs the glow plugs to cycle but they don't.

I have the 2000 article reprint compilation and plan on modifying my glow controller as it suggests. In the article it mentions not only replacing a resistor to lengthen the first glow cycle, but the possibility of replacing a second thermistor to allow warm glow cycles. The article says an update will be given when the author knows for sure. I searched the archives online and never found the update. Was this ever experimented with?

Thanks.

Joe

[crash9]

I

[Jgreemo]

A few users have recommended just shorting the two green (or yellow as the case may be) on the GP inhibitor. Just clip them and tie them together.

It seems the inhibitor duplicates a function of the controller to shut down the system at around 125*. I haven't done it yet myself as my GP problem was a balky relay. It also gave some problems like you described and with it replaced, the system works like a champ. Also, those high current parts tend to corrode fairly quickly, so you might want to check it.

jon

[ElGracho]

Thanks for the replies, but I'm not talking about the temp inhibit switch external to the controller, I'm talking about the thermistor inside the controller that prevents it from operating when hot.

[crash9]

Looking at the diagram in my manual doesn

[dieselbegreat]

crash9:
that sounds like a pretty good mod. I had a problem with my temp inhibit switch connection (no glow sometimes at all) so I just shorted the two wires together (yellow and orange I think) and I get similar results to you. The glow plugs now behave more often like they're cold, and when the engine is medium warm and the air is cold, they will light for about several seconds, go off and not cycle at all.

[More Power]

The simplest method to lengthen glow cycles is to add a 5 to 10 ohm 2-watt resistor inline with the Pin C lead (yellow) on the controller connector. This'll add somewhere between 4 and 8 seconds to the 1st cold glow duration.

However, this won't solve a no glow when warm problem.

The most often reported cause of a no start when warm (without glow) is "low cranking speed" due to a bad starter/cables/batteries (affects injector pop pressures & cylinder compression pressures), or a worn fuel injection pump/injectors. In other words, the finely atomized injector fuel spray isn't what it ought to be, and can't combust properly without glow.

MP