Al Spiker

My 96' 4.9 starts but "diesels" when hot. You can floor the gas and do whatever but it won't do anything but idle rough. Then it just "pops" and smooths right out and you are good to go until you cut it off again.Starts cold every time, just when it sits and heat soaks. Replaced coil, took IAC off and cleaned out, bypassed egr but nothing has helped. Any thoughts out there on how to fix this. Engine code suggest running too lean.

raski

Check for present and past stored codes. Some possibilities to "test" for are drippy injectors, coolant temp sensor (for pcm) sending the wrong information when warm and O2 sensor(less likely). On a 96, you should be able to see all this information on a scanner.

justintendo

almost guarantee weak fuel pressure. need to check it

raski

Weak fuel pressure would be more problematic on a cold engine where fuel demands are higher.