I have an '89 7.3. Can anyone tell me how the GP controller senses engine temp.. I am wondering because my wts time is down a little with new GPs in and I realized that this could coincide with installing an auxilliary temp gauge, sender in the temp light port. I will look in my repair manual but it's not handy right now.

 

I think that your new glow plugs are doing their job better then your old ones. When you say there a little faster, how much is a little?

 

I believe the controller goes by the resistance in the plugs. The warmer they are the greater the resistance the shorter the glow time. Thats why you get very short glow times when you have a burned out plug.

 

About 8 months ago my GP cycle abruptly dropped to a few seconds so I tested GPs and found several had to be replaced. I decided to change all of them as I bought this truck used some time ago and figured that if some were going the rest couldn't be far behind. I could only get four at that time so I ordered four more(Bosch, made in Japan. I know, i know now). I swapped out the four and when the rest showed up I put them aside. Weather has been warming lately and I am not plugging in regularly so I noticed starting was a little harder. WTS time about 8 seconds. Now, as I said, I installed an auxilliary temp gauge to verify the stock gauge, about 6 weeks ago. Being that I was plugging in, WTS time was. reduced anyway so I didn't notice any change at that time. Yesterday I had some time to kill so I decided to change out the ramaining GPs. The old plugs ranged through a Beru, a Champion(burned) and the rest were Bosch, made in Germany. Anyway this morning outdoor temperature was predicted to be about 12F but wind came up overnight and was about 22, still a good test. WTS time was about 3 seconds, RATS. Plugged in and fired up the old gasser to head off for a job. I got to thinking that maybe a couple of the GP plugs were not making good contact so I checked them all when I came home at lunch and having been plugged in for a few hours WTS time was about 6 seconds. I have read about controllers sensing engine temperature and something about a probe so I got to thinking about the sender I took out and wire I have disconnected to install the mechanical temp gauge. Kind of a windy post but trying to be thorough.

 

Did you test the 4 that you put in 8 months ago? Some of them ****ty plugs will go out on the first try. I don't know about the temp sensor. When there all working they should come on for at least 12 seconds, first thing in the morning.

 

Yeah, I tested all of the plugs for continuity with the test light method. I ordered beru's from rockauto but I won't put them in until I do injectors and return system. I can always plug in for an appropriate length of tme until then. This engine temp thing has me wondering is all. WTS time is noticably less when plugged in.

 

You can keep going round and round with the controller, and you might finally get it. Check the connector on the pass side inner fender and see if the two large yellow wires are melted in the plug.

When you finally get fed up with it, just convert it to a manual switch. It's the best thing I ever did to my truck, and I saved another little f350 dump from being sold by putting a manual glowplug switch in it. The owner comments all the time how it starts so well now with the pushbutton I installed.

 

The only thing sensing temperature in the engines with the new style controller is the glow plugs.

Resistance gets higher as the temperature increases.

That is also why the new style controller is so picky about glow plug resistance.
A glow plug with a resistance measurement of 5 ohms will still light a test light.
But it will contribute to a glow time short cycle since the resistance is so high.

Ideal glow plug resistance for the new style controller is between .5 and 1 ohm at room temperature.

 

Thanks all. I have some time this week to tesy my way through plugs, wiring etc.. The momentary switch sounds like an excellent alternative.