This problem started a couple weeks ago after i pressure washed the engine to find an oil leak. The engine idles fine, but when i accelerate from a stop it stumbles and unless i give it more than half throttle then it takes off like normal. I did find a couple vacuum hoses that were degraded so i replaced those, but still no help. I changed both fuel filters with same result. I also have a slight stumble when i accelerate at highway speeds. It feels like im driving into a very strong headwind when it happens. Im stumped at where to look next??? Please help

thanks
Eric

 

Are you using only Diesel Fuel?
Does the problem seem worse when the Fuel Tank is closer to empty?

There could be a problem with the Fuel Supply System.
If it drive normal with the Fuel Full Cap off your Fuel Tank Vent is restricted.

It could be that the Fuel Supply/Lift Pump is not up to par

The Fuel Injection Pump Pressure Relief/Overflow Valve could be no up to par

I am not sure if a restricted Fuel Tank Screen would cause your symptoms or not. But, it is easy to check for that.
Make sure you have at lest 1/2 tank of Fuel and swap the under the positions of the Fuel Inlet Hose with the Fuel Outlet hose where the hard Tubing’s come off of the Fender Well. That will bypass the Fuel Tank Screen and draw Fuel from a higher position in the Fuel Tank.

For good measure clean out you Crankcase Ventilating Tubing. The Crankcase Pressure can have an effect on you Vacuum Shutoff Valve.

 

Ive replaced all the filters (air and both fuel) thinking it was a bad tank of fuel. but no help. It has the same symptoms weather the tank is full or almost empty. Im leaning towards a vacuum leak of some sort?? like i said it all started after i washed the engine.

Ive been tracing all of my vacuum lines and found a couple hose ends that were broken, those have been replaced. What is the black box on top of the valve cover control?

What are the specs for lift pump pressures/volumes?

Thanks
Eric