Ford 4400 Injection Pump Update

Bryce Frazier

Well-known Member
Okay, so today, I cracked the 5/8 return line banjo loose on the back of the pump, it immideatly started flowing fuel. I completely removed the bolt, and there was a steady/constant, medium paced stream of fuel coming out of the pump. I inspected the banjo for an obstruction, but I couldn't see anything, and I could easily blow air through it. I put that back together.

Then I checked both of the fuel supply lines going to the pump, they both had about the same, constant and steady fuel stream. Not a whole hose full, but a seemingly plentiful amount.

Next, I removed the return line from the 1 / Forward cylinder. It had diesel in it, but wasn't full. I fired the engine up, and ran it to about 1/2 throttle, and after about a minute, it was just sitting there like, drip drip drip, but not a steady stream (was waiting to see if it needed to refill the line after I had removed it at the pump earlier and let it drain out). It continued drip drip dripping for about 2 or 3 minutes, then I pushed the hose back on and called it quits for the day.

SO. The injection pump on this tractor is only about a year old? Maybe a little more? What I don't completely understand is WHY there is fuel returning to the tank. Is it like when the pump starts to wear out, it will start to have blowby, and return more and more fuel? And does that explain why my brand new pump, doesn't return any fuel?

Also, if that is not the case, how worried should I be that it isn't returning fuel, and what are more tests I can try? Thanks!
 
On the pump side there's a two bolt cover, with a return line on it. There's a spring loaded ball check fitting inside that cover to pressurize the housing during running. If that valve is damaged or missing, pump won't have housing pressure, AND also won't force fuel out the top banjo bolt as it should. If I recall the banjo bolt side orifice hole is .020 inch in size, Perkins used on similar on there engines, but also had a supply feed pump Ford CAV DPA pumps don't use..
 

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