This just started a few days ago. When I first start the engine it runs smooth.
After it warms up it starts to tap. I bought the truck used and I am not sure what regular maintenance was done. Could this be the lift pump, Valves?
Does anyone have any suggestions????

 

fill in your signature so we can know what year and model and mods you have to the truck..... then we can help you more....

 

Sorry,
Basically everything is stock. 1998 12 valve dodge diesel. Straight exhaust. THats it.

 

that tapping noise can be due to a bad overflow valve. Mine tapped until i replaced it, i've also seen a bad lift pump as well.

 

lift pumps will sometimes make a ticking noise while they are starting to fail. It is just a plunger pump with 3 one way check valves that beat themselves apart (non replaceable). Use a hose about 1/2 in or so (heater hose is fine) about 2 feet long. Hold one end to the pump and listen in the other end (the clean end). You will hear the noise loud and clear if it is there. If not, keep going around the eng until you locate it.

 

They are easy to test if you have a fuel pressure gauge.

SFB