While it is cranking but not starting, are you getting any smoke from the stack? A total lack of smoke should indicate a lack of fuel flow through the injectors, and we can go from there. I am operating under the assumption that the truck is cranking with sufficient speed and isn't suffering from some other malady such as overheating... That also goes for the quality of the fuel. While Multi's by design are not overly picky about fuel quality, anything can get sticky if left to sit long enough.
First, make sure the electric lift pump in the tank is running. This switches on with the main power switch on the dash, and can usually be heard standing right by the tank. I seem to recall that one other member here has reported a hot start issue because his fuel pump wasn't operating correctly. Its rare but not totally unheard of for the pump impeller to fail, leading to a loss of pumping action even though the pump motor still runs. A bit later in the diagnosis, it might be wise to crack a bleeder and cycle the pump to see if its pushing fuel. Might be a good time to throw on some new filters too... Is the fuel new and fresh?
Does your shutdown lever (it looks like a plunger on the injection pump) travel correctly? Its conceivable that it could be sticking out a bit when hot, perhaps holding the rack out of place.
If the truck is at the right temp, cranking well, and pushing fuel to the injector pump, that pretty much leaves the injection pump itself. Like most any petrochemical fluid, the hotter the fuel gets, the more it thins. A worn pump may not be able to build correct injection pressure at cranking speed with thinned fuel. The increase in RPM from the ether might be enough to get it over the crest, so to speak. A pump plunger or governor linkage stuck from extremely old dry fuel might act the same way, exacerbated by the heat.
A buddy of mine called me recently about this exact problem with an old loader he's got. A tank of fresh fuel treated heavily with 2 stroke oil and fuel treatment has him going again, your results may vary...
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