I have a Cat DP30 forklift with a 2.3l diesel engine. I have replaced the fuel filter housing, fuel filter, all the rubber hoses, even the fuel level sending unit inside of the tank. I have used an air line to pressure up the tank and sprayed a soap leak detector on all of the lines and can not fine any type of leak what so ever. yet it will lose prime every day and sometimes several times per day for a few months and then I will not have any problems with it for a few months. Any thoughts on what else to check? I am wondering if I have an internal leak inside of the injector pump.:Banghead
Not sure what type of fuel pump is on it, but that's a possibility, is there an inline fuel filter or a screen somewhere inside a fitting you haven't found, I've had it in the past, when the line in the tank has a crack, it can suck air when the fuel sloshes in the tank. I've also had to replace all the copper washers in the fuel system, they didn't leak under pressure, but would suck air somehow and lose prime that way, if there are any in the system, replace them all. I've had to in the past, reseal the fittings that hooked everywhere in the system in order to solve this issue. Not sure I was any help, since I'm not familiar with this machine, but most fuel systems are similar.
Does the fuel cap have a vacuum on it when you open it. If there is a vacuum on it then the vacuum on the tank might be draining the fuel system and therefore losing prime.
When it loses prime what do you have to do to get it to start running again ? Is it possible that the engine is being shut off by an intermediate problem with an electric shut off ? Possibly even an ignition switch problem if the engine has an electric solenoid or lift pump. When the lost prime situation is present is there fuel being delivered to and through the fuel filters ?