1990 W250 difficult starting

[Ironforger]

Does anyone know the best way to purge the air from the injection pump? Is there a bleeder screw anywhere? My 2nd gen VP44 has a schrader-like bleeder screw on the side of the IP case which makes it easy, but I don't see one here on my first gen.

I'm going to need to purge it once I install my new lift pump.

thanks!

[DodgeFreak]

crack the fuel lines, there is a bleeder screw to bleed the air from the filter, then once the air is out of there pump the fuel some more then crack some of the fuel lines and crank it over.

[Ironforger]

crack the fuel lines, there is a bleeder screw to bleed the air from the filter, then once the air is out of there pump the fuel some more then crack some of the fuel lines and crank it over.

Tried this, still not starting.

I changed the lift pump. Seems like I'm still getting air somehow. So, I took off the fuel supply line at the IP, submerged it in fuel a clean clear bottle, pump the lift pump and it's still pushing air bubbles.

So, now I think I may try to rule out a cracked or leaking fuel line between the lift pump and tank. I'm going to take off the supply on the suction side of the lift pump, and dip it into a full plastic bottle of diesel then pump the lift pump to see if its still puttin out air.

Thats the only thing I can think of for now. I feel like I gotta rule out why the it's putting out air bound fuel.

Any other suggestions greatly appreciated!

[opiebennett]

Could have a crack in the line feeding the lift pump, so when the lift pump pumps, it's pulling fuel from the tank, and air in via the crack.

I'd expect a crack between the lift pump and the ip wouldn't add air to the fuel, as the fuel would be pressurized, so air wouldn't get in. However, fuel would get out, and you would see it (leak).

With a crack before the lift pump, the fuel line is a vacuum with respect to atmosphere, so air would be pulled in.

[Ironforger]

Ok, so it's finally warming up here in NJ. I'm going to work on it this weekend.

If I'm able to rule out a cracked or leaking pre-lift pump supply line & it still wont start, my next test will be to rule out the fuel solenoid on the IP. I read in my shop manual of a method to test it by removing plunger and spring. Then if it starts up I can kill the engine with the mechanical shut down lever.

Any other suggestions welcome.

[Ironforger]

Fixed.

Diagnosis: Supply line leak pre-lift pump. Supply/suction line was rusted. There was a small hole at the first bend off the tank.

I ran a new rubber fuel line (Diesel compatible of course) from the tank to the lift pump. Luckily didn't have to drop the fuel tank. Being skinny and working from the driver side rear wheel well I had just enough room to reach up under the body to remove old line from fuel tank and clamp on new rubber line.

Once the new line was in I purged everything as follows: loosen the inlet banjo bolt on the fuel filter housing, operate hand lever on lift pump until fuel squirts out, tighten banjo. Next, removed fuel supply line at injection pump & place in small plastic bottle (spring water bottle). Operate lift pump hand lever until clear bubble free fuel squirts out. Replace fuel line, but don't tighten. Operate lift pump again until fuel leaks out around fuel line nut. Tighten nut. Next, cracked all injector lines on the head and cranked engine until fuel squirted out all lines. Tightened all injector lines & truck started up. Runs fine now.