glow plugs wont stop cycling

[dylank]

on my last road trip with my 84 gmc rally stx van, i noticed about halfway through that the glows plugs had either kept cycling or started cycling again after about an hour of driving. the battery meter always reads full after it turns over and cycles a couple times and stops, but this time it was staying in the middle like i was cold starting and then dipping down to about 1/4 when the glow plugs would cycle. it kept doing it the whole time till i got home, it drove fine, but the glow plugs kept cycling. just had the glows plugs and controllers replaced about a thousand miles ago, also put in two new battteries 500 miles ago. havent had this problem before, but ive only driven the van about 5000 miles. ideas?

[NH2112]

Dr. Lee is going to say it, Britannic is going to say it, and at least 1 other person is going to say it, but I'm going to beat ALL of them to the punch - upgrade to an 85-93 glow plug controller!

The early glow controllers were pretty complicated pieces of equipment - a 12V feed from the alternator caused a thermal switch to open, de-energizing the glow plug relay and keeping the plugs from glowing. The usual problem with this setup was that if the alternator diodes were bad battery voltage would get through and keep the circuit de-energized when it should be energized. Continued glow cycles are an indication that A) voltage is no longer coming from the alternator to keep the thermal switch open (bad wire, bad connector, bad alternator) or B) the controller itself is bad. The 85-93 controller doesn't run much over $60, which is a lot less than the older style goes for.

[ 09-07-2003, 06:53 PM: Message edited by: NH2112 ]

[Low_Bridge]

Because of the great information on this forum and being a contol freak I yanked that stuff out. Put in all new 60's glow plugs and a momentary switch. On a hot day I don't even need glow. That controller stuff is a real syndrom!! Kinda like windows 3.0. I now know, "what it is to control the glow" Thanks Diesel Page!

[dylank]

ok thanks, a couple more questions..how tough is it to install the glow plug controller myself? where would you reccomend getting it? also, my van has a rebuilt 85 engine in it, would this mean that it is already utilizing the newer glow system, or does it probably have the 84 system still in it? thanks.

[NH2112]

I'd recommend getting a genuine AC Delco controller, they're available at the dealer or you can check if any parts stores carry them. As far as whether or not your engine already has the newer style, the best way to tell is to look at the rear of the driver's side head - if you can see a light grey controller, without a separate relay mounted on the left fender or inner fender, you have the new style. Installing the new one in an old-style truck is pretty simple, nothing more than a matter of hooking the original wires up to the proper pins on the new controller (you'll need the 5-pin connector for the new one as well.) I posted a procedure after comparing the schematics one day but I'm not sure if it survived the crash of a couple weeks ago. I'll see if I saved it on my PC and repost if so.

[burbans2]

Please also tell me how to convert to the newer style controller as I have gone thru at least 4 of the older style controllers myself. the present controller that I have works well when the engine is cold, but sometimes shuting down the engine and restarting in a few minutes on a hot engine will cause the glow plugs to begin cycling again. I just raise the hood and unplug the relay on the drivers side inner fender and replug when the engine is cold. Thanks