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Discussion Starter #1 (Edited)
I just finished getting the 4b in my boat restarted after having sucked air from the fuel tank. This is the second time I've done it in recent years and am surprised at how long it takes to get it to fire after confirming fuel through the high pressure (HP) pump. After the first time sucking air, I installed a rubber squeeze bulb on a shunt to hopefully make this an easier process. Using the bulb I can apply low pressure on the system and confirm no air at the 1) Racor, 2) Fuel filter intake, 3) fuel filter outlet, and 4) bleed valve on the HP pump. After this, I crack the injectors and turn the key. Typically it takes a total of 30-60 seconds for fuel to start leaking at the loosened injectors.

How much cranking following this should it take to clear enough air in the line for a start?

I went through 6 or 7 sessions of cracking all 4 injectors, turning the key 2 or 3 times for 10-15 seconds, tightening the injectors, and then trying for a start before it started. Is there anything I am missing here? Is this pretty normal? Thanks in advance.
 

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Which injection pump are you dealing with? Is this your original 4B engine in the first boat or a different one. One recommendation would be to add a fuel pressure gauge to your instruments if you don't have one. You could have a weak lift pump or a restrictive fuel filter. The rotary injection pumps like fuel pressure in the 7-10 psi range, although they will run on less. The inline P pumps like around 30 psi. If you've cleared the air out of the lines prior to the injection pump, you should get more than a dribble out of the high pressure lines at the injectors.
 

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They will normally start on their own with 30-60 seconds of cranking if you have the fuel system bleed properly on either the inline or rotary pumps in my experience. It seems every once in a great while I get one that just doesn't want to start at all, not sure why but it happens. Had one once I actually convinced myself I sheared the key off somehow, pulled the pump back off and it was intact just as it should be. I installed it again and bleed the fuel system again and after about two minutes of cranking again it finally took off.
 

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Discussion Starter #4
All good information and feedback, thanks for the responses. Here is a picture of the business side of my motor showing the hp pump and spin on fuel filter.

I am surprised at how little fuel I ever see coming from the loosened injectors. At the end of the process, there seems to be less than 1 tablespoon in the area of each of the injectors. Given that at operating rpm (2100) I burn 0.85 gph, converting to ounces, dividing by 60 minutes, then dividing by 4, each injector should be getting about 0.44 ounces per minute, or just under 1 tablespoon per minute. I have never seen spraying fuel at the injectors while cranking, only dribbles. Still seems as if there should be more fuel around during the process.

I'm trying to get a good handle on this so if this ever happens when I am in the middle of nowhere, (I live in Alaska) I'll be able to restart and get home. Below is a picture of my rubber bulb shunt that I set up after my first air in the fuel system event. Having it in place greatly sped things up yesterday.


Thanks again for the feedback.
 

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I use a 12v electric fuel pump to purge. You should be getting more pressure at injectors. When I wasnt, my pump was out of spec. Rebuilt and juice hits the hood when inj are cracked. I rarely have to do more than one injector bleed session to start now. 6 or 7, somethings wrong.
 

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That is a Lucas CAV injection pump. Not one most of our guys will see since it wasn't used on a a road engine. Typically, when you crack an injector line once the fuel is there, it would hit the ceiling because it's under so much pressure. You might have one or a number of issues at work. Weak lift pump, weak injection pump, or injectors that need rebuilding. If the injectors aren't popping at the correct pressure, the don't allow the pump to build pressure. You can pull them and have the checked. Usually not an expensive deal. If they check out then you've eliminated that as an issue. Weak lift pump can mean hard starting or engine stopping after it's fired up. If it has the diaphragm type lift pump, those are notorious for short life. One problem that can happen is when the diaphragm fails it leaks diesel into the oil pan. Those pumps are inexpensive and carrying a spare isn't a bad idea, especially on a boat. A weak injection pump can have some of the same symptoms as the other two. Working on the IP can get into a lot more money. Another thing is check all your fuel fittings and lines to make sure you're not sucking air somewhere. I see you have some clear fuel hose and that is an excellent idea. If you see air in the line then you have a problem before that.
 

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I have no experience with the CAV pump but from what I see you have a lot of system volume on the inlet side. The greater the volume the tougher & slower is the bleeding.
 
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