Article By: Jim Oaks
I had problems with my 1989 F-250 7.3L diesel stalling after start up on a cold start. It would start and run for about (3) seconds and then stall out. Afterwards, it was very difficult to re-start. Once the truck was running for a while, it would re-start fine, but if it had been sitting for a few days, it was difficult to start. After searching the internet for answers, I decided to post what I found here.
Mechanical Fuel Pump:
This can be a symptom of the mechanical fuel pump (lift pump) on the engine losing it’s prime. One way to determine this is to park the truck with the front facing down a hill. It should start fine if pointed down hill. The fix, if this is the only problem, is to replace the mechanical pump. Fortunately, it is easy to do and not expensive. This is a good upgrade irregardless. My F-250 already had this conversion, so it was on to something else.
Sending Unit:
Now if the electric pump doesn’t solve the problem it’s time to drop the tanks and check/replace the sending unit/pickups. There is a plastic extension on the bottom of the pickup which contains a one-way valve and the filter/screen. Unfortunately, this plastic part breaks off and or the one-way valve rots (rubber). This allows the fuel to drain back into the tank whenever the engine is shut down. If the plastic has broken off at the top where it attaches to the metal tube of the pickup (as both of mine were) you’ll run out of fuel at about the 1/4 tank level. The new sending unit/pickup is a Ford dealership only item, and costs ~ $95.00 each and the front and rear units are different with different part #s. While the tanks are down check carefully for rust/pinholes that are about ready to start leaking fuel. Again, parking the truck pointed down hill can help by preventing the fuel from draining back in to the tank.
Air Leak:
Take an air compressor and blow air in to the filler neck of the fuel tank. Use a shop rag to hold around the hose to try and seal it. Have someone check the fuel lines under the truck for fuel leaking out or air hissing. You may also choose to remove the fuel filter, place a container under the filter mount, and blow air in the tank again. Fuel should come out of the filter mount.
Return Lines:
Check all return lines, T’s and O rings. Someone reported finding an air leak on the return line setup right below the fuel filter. They changed O rings and hoses five times before finally changing the cap itself. Come to find out that the cap had a pinhole that would not leak diesel out, but would let air in when the truck sat for more than 30 minutes. Letting the truck sit downhill kept diesel in the fuel lines without an air intrusion. Once the truck was parked level the fuel bled back into the return line.