Wile E. Coyote
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Unfortunately there are many variables here. Next time it short-cycles, don't go to START, but return it to OFF. If you have a set of jumper cables handy and someone to serve as Soldier B, clip one end of one cable to a clean chunk of metal on the engine block, and have Soldier B hold the other end to the clean and shiny top of one of the 7/16" head control box mounting bolts near the main electrical connector under the hood just in front of the driver. Turn the switch to RUN. If the WAIT light stays on this time, you very likely have a grounding issue (very, very common.)I just had the short cycle light on a cold engine. Garage is 40 degrees
engine started well though and I was able to use the truck. I left it running the whole time. It is 9 degree Fahrenheit outside.
Ugh. So I’ll be crawling through all this info as well. Should it have started so earsily if the PCB box or relay box failed?
I've had boxes that didn't turn on the WAIT light or short-cycled the WAIT light despite the fact the system was still cycling the glow plugs correctly. If you suspect that might be the case (because the machine started after all) - next time you try from cold and the WAIT light short-cycles, look and see what your instrument panel voltmeter is doing. You can usually detect the glow cycle by the change in alternator note coupled with the action of the voltmeter (and the headlights will dim a bit if you have the old sealed-beams), and after the initial glow period most boxes will continue to cycle the plugs a few seconds on, a few off, and on again for the Afterglow period.
Have a look under the dashboard behind the steering wheel at what type of control box you have fitted - specifically the label. You need to note the label color and manufacturer at the very least, and a p/n if you can see one without having to remove the box. That will tell us what generation of PCB/ EESS/ S3 box and system you have. If you still have one of the original Prestolite silver-label things that the USMC stuck with for years while everyone else tried other things - those are 30-plus years old now. I have a stack of them with failed mechanical relays.
The other boxes that work with or without a temp sensor are all solid-state except for one model with one relay, from what I remember, but the solid state ones don't like uneven glow plug loads (which is why they say to replace all the glow plugs as the same time you install one of the newer type boxes - so the spectre of that particular problem never crops up.) For those boxes, when you have a few burned-out plugs, some types of them will short-cycle the glow light. At that point sometimes you get away with just changing the glow plugs out (as a set) and trying again - and sometimes - you don't (like pretty much every KDS Green Label box I've ever come across which blows the SCRs like expensive fuses.)
As a matter of course I would measure all the glow plugs with a meter if you have one. Pull all the orange hoods off, pick a low Ohms range on the meter, put one probe on the tip of the glow plug and touch the other to a clean ground. Bad ones will read 0.00 (or whatever you meter usually reads to indicate infinity) which indicates the heater coil is open. Willing to bet you have 3 or 4 bad ones.
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