I've been thinking about the manual control mod that several folks around here have done and am debating doing something similar - but with a little twist.

The biggest problem with the stock controller is that when they go bad they have a tendancy to cycle the glow plugs on while the engine is running, and this damages the glow plugs, right?

Well, the idea of replacing the controller with a hot wire directly to the relay is a good one, but I see 3 minor drawbacks to it.

1) you never know for sure whether you need to use it or not - i.e. whether the engine is still warm enough to start without them, and
2) you never know if you are turning them on long enough, too long, etc., and
3) you don't get the benefit of seeing the controller short-cycling to tell you when some of the glow plugs have gone bad.

Here's my solution. Instead of just bypassing the controller with a hot wire controlled by a pushbutton, why not simply cut the wire from the controller to the relay, and splice your pushbutton into the wire where you cut it. I'm also thinking of mounting an LED somewhere up higher on the dash and wiring it in parallel with the existing "Wait to start" light bulb. That way it will give me a better heads-up visual indicator.

This way the controller can cycle all it wants to, but the relay will only energize when I'm holding down the pushbutton. Of course the heads-up LED indicator will only light when the relay is energized.

The way it would work is that whenever you're starting the truck you push the button (just like a manual control) but the glow plugs will only turn on if the controller would have turned them on due to temperature, and they will only turn on for the amount of time that the controller would have cycled them on. You just hold the button until the indicator light goes out, and once it starts you let go of the button the controller can't keep energizing the relay. This way you still get the use of the startup timer and temp sensing functions of the controller - without having to worry about it malfunctioning and burning out your plugs.

Of course if the controller ever stops functioning altogether, converting this setup to a straight manual control will only require moving one wire - from the controller output to the battery. What do you guys think? See any potential problems with this idea?

 

I've wanted to try something like that for a while now, just never had the chance. Problem is when you get around to doing the button, usually the plugs and controller are all burnt out already, so most people don't want to spend the extra $$$ to get a new controller. I say if you can catch it before it's all gone bad it should work.

The only drawback is sometimes on the old trucks it isn't just the controllers that take out plugs. Sometimes you can get weird ground loop problems that will burn out plugs by just bearly lighting up the 'wait' light. They say it's usually from bad wiring in the engine harness or a bad diode in the alternator. In any case make sure the ground wires from the engine to cab are clean and tight and the wait light wire isn't connected directly to the glow plug wires on the solonoid.

Another problem area on the old trucks is the engine harness connector, make sure the glow plug wires aren't burning up the plastic of the connector.

 

Well, except for the problem with cycling them on & off after its running (when they don't need to be) the rest of the system seems to be in good shape - now that I've replaced the plugs and the relay (everything BUT the controller)

 

Sounds good to me.

On really cold days you will need to afterglow or the cylinders will cool off during idle and the engine might stall. This is the reason the factory controller cycles even after the engine is running.

For what it's worth, I have yet to have a problem with my controller. All my glow circuit problems were always glow plug related.

About the only time I don't like the way the controller glow the plugs is in the spring and in the fall when the temperatures are just above the set temperature where the controller would glow for longer periods of time. During these times starting gets a little bit more difficult as the plug just don't glow long enough it seems.

Seb...

 

The 86 and earlier glow plug controller does not short cycle when the glow plugs are bad. No resistance feedback to set the heat time. Engine coolant temp below 115 degrees and a timer controls how long the glow plugs stay on. Afterglow is also controlled by a timer that starts when it recieves current from the alternator after a start sequence. Those timers don't care if there is 1 or 8 glow plugs working.

The 87 and later system uses glow plug resistance to determine the length of the glow time and will short cycle if some plugs are burnt out.

The first problem I had with my 86 system was the controller. At that time a new one was 200 dollars. Went to manual control and never looked back. The only disadvantage to manual glow plugs is someone else driving your truck. You will develope a feel for how long and when you need them.

You could wire something like that up, but the wiring would be different for the two systems.

 

Hmmmn, that's weird. Mine behaves like there is more to it than just a timer, Dave. It comes on for a set time at cold start, but then after that the frequency and duration of how long the glow plug light comes on seems to vary with conditions. Sometimes it cycles off and on for a few seconds at a time for a couple of minutes. Sometimes the on cycles are longer than others. Maybe it is just operating erratically. Either that or it is more complicated than what you describe.

 

I have a book here that goes into the 83 thru 86 glow plug diagnostics. About 10 pages of them.

Great system till it goes bad, then it is nothing but a nightmare.

The new style system on the 87 and newer ones has 1/2 page.

 

jeepers check your ground on the controler and the relay mine was aslso doing the samething then after new grounds on both now works fine

 

I don't suppose the two systems use the same controller either do they? Just wondering if it might be possible that mine is a "late" 86 that got the 87 style system....

 

do you have spade or bulet type gp some have done the solid state conv to there ride as soon as i get the cash flow back my way thats what i plan on doing so ya never know about these old but faithfull beast

 

Mine has spades....

 

BTW, that part sounds like a good "theft and unauthorized use deterrent" system to me!

 

Nothing on the 86 and older glow plug systems was used in the 87 and newer systems.

They are completely different systems.

Yes it could be a theft or unauthorized use deterant, but it may cost you a starter.
Until I lowered my compression I never used the glow plugs at all when the temp was over 60.
Now I give it a couple seconds just to make it easier on the starter.