Combines Air in fuel filer Hard starting problems

Did you change filtersIJ Did the problem start all of a sudden, or gradually over time has gotten worseIJ Is your water separator above or below level of fuel tank. If above their should be a check valve to keep fuel from draining back. You could have a chunk of debris holding it open. The check valve should be a fitting between fuel tank hose and filter head, usually mounted on the filter head. Had this happen on the 4 wheel drive. If and hoses have hose clamps tighten could suck air. Hope this helps.

Another thing to check is the fuel tank filler cover. Air holes have to be open to let air displace fuel as it gets used. Remember, if air gets in the system, your problem has to be above the level of fuel in the tank otherwise, there would be a visible fuel leak.

I agree with Tom. Check fuel filler cap air hole. It must be clear. We used to put a small tin can over the filler cap to prevent dust blocking the air hole. I have seen air sucked pass an O-ring fitting on a fuel line into a fuel system when the air hole was blocked but when the engine stopped the O-ring relaxed into its original seat and no leaks were obvious. If a small amount of air is getting into the fuel while running, there will be a reduction in power which may not be obvious until the leak is fixed. A second possible problem area is that I think [ but am not sure ] a small metal mesh filter is located in the fuel tank on the fuel outlet pipe. This may be able to screwed out through the fuel tank outlet or may be accessed by hand through the filler cap. If this filter is partially blocked this will have the same effect as a blocked vent.

This is a real puzzel. The restriction should NOT come on because of air, just the opposite. Therefore if the sending unit is ok then you have a restriction somehwere in the line. If it were in the filters it would come on under load. Also IF the water separator is in stock location it is below the tank. Therefore it is impossible to have air migrate downward ( assuming you do not park the unit upside down - ) logically the air would come from the fuel pump side then. When changing the fuel filter last time the old gasket sometimes used was not left on the filter baseIJ I would remove all the lines, flush them and inspect for bad tube seals, loose crimps if yours has the flexible lines, replace the seals and check the filter bases for warpage or leaks. If your unit has the fuel filter plug on type there is a roll pin on the bottom of some filter bases than needs to be removed as this caused a restriction. let us know what transpires.

I'm thinking you have Ambac fuel pump (I believe all l3s did). You can check fuel tank screen by reaching down threw fuel fill cap an pulling screen off of fitting. It could be restricted which could cause air to get by gasket on bleed screw of water seperator filter. If screen is missing you could have chaff stuck in fitting or fittings between bottom of tank and first filter. You likely have the spin on water seperator filter and it would likely have the seal washer with rubber on its ID. I have had to use sealant on these washers to get them sealed up tight. It may not leak from static fuel pressure but suck air while at slight vacuum. Fuel restriction sender is on final fuel filter head on these systems and is looking for some charge pressure so this may all make sense. Good luck