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FYI, before you replace that injection pump...


New Recruit
Fleet Manager
I'm feeling generous since Hino 123 helped me resolve a problem. So, I'd like to pay it forward with a little tip. Did you know there's a little strainer inside a banjo bolt on the injection pump? One more place where fuel can be restricted. Customer's Hino crank, no start. Fuel rail pressure wasn't getting up to commanded pressure. Checked fuel filters, filthy! Replaced them. Even replaced the "bubble separator" (see below for more about the bubble separator). Now it starts and you can rev the engine all you want. But when put under load, like actual driving, you can throttle up for a split second and then it loses power. Graphed rail pressure again, Fuel Rail Pressure (actual) and Target Rail Pressure (desired/commanded), and found actual rail pressure would meet target for a split second, then drop off. So, it still seemed like there could be some sort of restriction. Hooked up a 12V lift pump with a hose at the farthest point possible, after water separator, before injection pump. You can use a hand pump. You can use your mouth, but you'd have to be willing to drink some diesel. You'll want to pump enough to make sure it can sustain unrestricted fuel flow. I pumped out 2 gallons of diesel with no problem. So the problem has to be the injection pump, right? (Technically could be the suction pump as well, as it's bolted on the injection pump as if they're one unit.) Well, there's one other thing, the SCV (suction control valve), mounted on the suction pump portion of the injection pump. This is basically the fuel pressure regulator. We replaced it. Still same problem. Started to remove banjo bolts to the suction pump / injection pump in preparation to replace the pump. Then we found A STRAINER INSIDE A BANJO BOLT. We pulled it out of the bolt with pliers. Completely clogged. Cleaned it out. Reinstalled. Problem fixed. Someone told me there is a strainer inside another banjo bolt in that area; either on the injection pump or one of the bolts to the bubble separator.

Bubble separator: That's the thing that looks line a small spin-on fuel filter just above the injection pump. On some trucks, it's just an empty can; nothing inside at all. But if you get a replacement filter, they now have an actual filter element inside. So, it's another place for fuel to get clogged and another thing that needs to be serviced periodically. They originally didn't design this to be replaced often, though. To remove the filter, you have to remove the housing. To remove the housing. It's 2 mounting bolts and 3 (or 4?) banjo bolts. Then (the fast way) you have to bend the fuel lines out of the way. Or (the slow way) loosen or remove the other ends of the fuel lines. The slow way will take you 1 hr more if this is your first time. Personally, if I find out mine is the empty can type, I'd put it back and never worry about removing it again.
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Seasoned Expediter
Nice post moocowman. I just wanted to add 11-14 Conventionals have a “bubbler filter” with no actual fuel filter element in the cartridge. On 2015 and up Conventionals (not a cab over and has a hood FYI) there is a filter element in the filter. The service interval is 84 months or 240k miles! I personally advise to replace them every 2years or 100k miles. As far as installing a new filter on a old 11-14 truck it is not recommended. The reason being is you are essentially now installing a restriction (5micron filter) where previously there was no restriction. Also is you replace just the filter and not the complete housing on a 11-14. The fuel “dink” actually interferes with the bottom of the 15-current. There have been reports of it actually chaffing a hole in the bottom of the filter and loosing fuel pressure/ fuel. Just wasn’t to add that.