I have an old Caterpillar 950, 73J3158M, that is hard to start when it's cold. I have had it for a few years, and it didn't used to be this bad, it seems much worse this winter. After a long glow, like 30 or 40 seconds, it takes a lot of cranking, during which time it coughs and fires and sounds like it is trying to run on one or two cylinders, then stops, more cranking does the same again. Repeat the glow, crank again, more coughing and half firing, before eventually starting up. It sounds like one cylinder is missing a bit at the start and then soon picks up. Once it warms up, it runs fine. I have tested the glow plugs individual current draw, one at a time with a jumper wire. They draw between 5.1 and 6.3 amps. They are all receiving power from the wiring loom. I have not tried to remove them. Is it possible for them to draw current but not heat up? How are you supposed to know how long to glow them for when there is no indicator light or timer? Can you burn anything out if you glow them too long? Anything else common to look for? Fuel draining back?
I don't know about the 950's but the instructions for my old 980B's Are for 1 to 3 minutes depending how cold it is. I would just run the glow plugs longer . How cold is it when starting?
I've got a newer Kubota that requires a minute or more when it's below freezing and used to have a Hino that required cycling the glow plugs 3 or 4 times. Also putting to full throttle helps. As soon as it runs healthy put to idle. The Hino I had to hold full throttle for about 20 seconds until the RPM's got to about 1200. Then I could let it off to idle.
I don't have an owner's manual, so I don't know what the instructions are. Perhaps I could let it glow for longer, but I was concerned that it might burn them out. 30 to 40 seconds has been sufficient for the past few winters, so something has got worse this year. The coldest it gets is about zero degrees Celsius, but even later in the day when it is say 10 to 15 degrees it struggles as I described.
I was gonna ask how cold is cold, 0 Celcius is cold enough if everything is a little worn like it will be on something old. What happens if you crank it five seconds with no glow plugs? watch the exhaust and see if you get nice even white foggy puffs from the first crank, or if they're mixed foggy and clear? you could try operating the primer pump a minute before cranking it to see if that improves the initial evenness of the puffs. Otherwise, old summer fuel will make some start real slow. What elevation is this thing at? How's the cranking speed? batteries in good shape? cables getting hot anywhere after cranking for a while? Sometimes an old starter just gets worn out and dragging, take it apart and sometimes it's easy to see what's wrong and fix it before the starter is burned out. Or, another popular choice is a brand new gear reduction starter, I don't know what's available for that engine. Other than that, a poor spray pattern from the injectors or poor compression would make it hard to start. How's the air filter and piping? a dusted engine is the most common way to lose compression quickly without noticing it.