Write up for replacing LPOP.
 

ok, 97 f350 psd, 296k

Whats been done:
new water fuel seperator/fuel bowl along with regulator and wiring harness/fuel bowl heater
fuel regulatorr is bumbed up with the old "BB behind the regulator spring"
Mechanical Fuel pump
One High pressure hose from the HPOP to the passenger side head (old one let go about 2k ago)
New sealing ring from mechanical fuel pump to the high pressure fuel lines (ring around the big banjo bolt)
Truck has a DP tuner with 6 stages, normally left in 80hp economy daily driver.
3" MBRP downpipe to custom 4" straight pipe


This just started about a week ago. go outside in the morning after the truck has been sitting all night, let the glow plugs cycle, and hit the key. the truck will fire up, cranking normally, and after about half a second, sputter and die. hit the key again for about 2 seconds and she fires right up and runs for the rest of the day. issue doesnt return until the following morning. so after warming up from driving a little bit, ill come to a stop, rpm's fluxuate from normal idle, slightly lower and rougher, above normal just ever so slightly, and comes back down and repeats, not a steady pattern, it can be faster or slower. Put the tuner back in stock mode AND IT ALMOST DIES when you come to a stop from 30mph or higher, or having the torque converter locked up. (i dont have a manual tc lockup switch, its whenever the truck says to lock it up.)

Now i am thinking either the HPOP is becoming weak after 296k, or there is a check valve that is failing, letting an air pocket develop either in the fuel system or oil system?

any ideas? i know theres a check valve in the fuel lines thats cheap VS the 600$ minimal HPOP.

PS there is no check engine light.

If you unplug the ICP sensor and start the truck, does it do the same thing?

haha i cant believe i havent tried that yet haha. i will try that tomorrow :tu:

but last time i had a scan tool hooked up to it i did look at that, seemed to be working right...

Another thing to check before starting the truck next time, Pull the plug on the HPOP res... Check the level of the oil inside. Should be 1/2" from the top.

I had the same issue. It is your LPOP. When you fire up the truck in the morning, the injectors are being fed by the oil in the HPOP reservoir. After running for a few seconds, they have used all the oil in there before the LPOP has come up to enough pressure to refill it. The problem is exaggerated in the morning because the oil is cold and does not flow as well.

I changed my LPOP for a Melling unit and its been great ever since. It seems to be a more common issue in trucks with more than 200K. Best price I've found is here: Riffraff Diesel: Melling Low Pressure Oil Pump LPOP

I attached the write up I did on the replacement. Its easier than it looks. Should take no time at all.