tbrumm
Full Access Member
I have been having some trouble with starting the truck after it has been sitting all day in the cold (below 10°). It starts very fast when plugged in, but can be very hard to start if not. I have new batteries, a new glow plug harness (oem) to the plugs, and each plug is in working condition. I seem to have a glow plug issue given the fact that the truck starts fine plugged in, so I did some diagnosis on the GP system. I checked all the wires from each glow plug back to the controller and all have continuity, which I expected because I put the harness in this summer. At the power terminal at the GP controller relay, I get 13v, which is the same voltage as the batteries. I should mention that my truck has a single large gauge wire running from the GP controller relay back to the fender solenoid with two fusible link wires connecting the cable to solenoid. This sure looks like a factory setup to me, so maybe Ford finally did away with the two overworked yellow wires through the wire harness connector in the last year of IDI production When the key is turned on, I get the full 13 volts at the other large terminal on the GP controller relay (where the metal "z bar" resistor is attached). I also checked the ground from the controller to the intake manifold bolt and that was fine, although I cleaned the loop connnector up a bit just to be sure. Resistance to the GP controller ground loop connector back to neg post on battery was 0.1 ohms. Finally, I pulled the connector of the No. 2 GP (easy to get to) and checked voltage at that connector while my Wife turned the key. I got a little over 9 volts, and I guess I expected 12v What should be the voltage at each GP connector if the system is working properly? I would guess that "z bar" resistor is stepping down the voltage? Anyway, I had a spare GP controller so I installed that just to see if that made a difference. With that controller, I got 10 volts at the No. 2 GP connector. I did notice that the "z-bar" resistor on the first controller was a bit discolored - very ligh bluish tint. Do those "z-bar" resistors go bad? Can't imagine it would as it is just flat piece of metal after all. The WTS light has been staying on about 10-12 seconds with either controller, but the spare controller does seem to be heating the plugs a little better - haven't tested it yet in temps below 10° yet. Sorry for the long explanation - just trying to give you all the details I can so you can help me diagnose this. I am not sure what else I can check now. thanks! Todd