3B Air in fuel line

Joined
Nov 16, 2010
Messages
365
Location
Squamish, BC
Stumped on where the air is coming from... the long description of situation as follows:
The vehicle:
My daughter's 1984 LHD Canadian spec 60 series 3B with 530,000km. Idles smooth at ~725 rpm. Valves recently adjusted, and compression measures 420 psi across all 4 cylinders (+/-10 psi), so not worried there. Engine was installed into LHD 1989 FJ62 about 15 years ago by previous owner, and has the FJ62 fuel tank with blocked off return line going into the gas tank fuel pump assembly. There is no diesel return line to the tank; no provision for it in the diesel fuel system components. Fuel/water separator was cleaned out recently and is sealed well. All soft fuel lines have been replaced with clear to try to track air leak.
The problem:
The air bubble always and only shows up on the soft line from the firewall hard line (left side) to the primer pump on the left side of the engine block. There is no fuel leakage at any of the banjo fittings on the primer pump, fuel filter, or injector pump (all copper washers are new). There does not appear to be any fuel leakage at the primer pump, which has had the manual Toyota hand pump replaced with a Bosch unit at some time by previous owner. The bleed bolt on the output line of the fuel filter was weeping diesel even with a new bleeder bolt. and so it has been temporarily sealed with a NPT cap (I know that's bad but it's really close to M10x1 thread, and the Toyota bleed banjo is NLA so this is temporary until I can find a M14x1.5 bleed banjo (new by other or used Toyota). With the cap, this area is no longer weeping. There are no bubbles in the soft line on the right side of the engine between the hard line at frame and firewall, none on either of the soft lines into and out of the separator, and none in the soft line from the tank to the hard line on the frame. There is no visible leakage on any of the hard lines.
The system can be successfully bled at the fuel filter outlet, and the bubble disappears (usually run about 1 liter of fuel into a container to make sure the air is out). The vehicle runs well, but after a 10-15 min test drive the bubble comes back (just like the Cat! Check out NFB Canada if this doesn't make sense). When the bubble gets that large, the truck has a really hard time getting up hill due to loss of power (particularly off road). The size of the bubble can vary; last night it was about 6-7cm long, this afternoon after driving less than 10km it's 3cm long (see photo). I've been trying to solve this for about 2.5 months and I'm :bang:. I have a spare FJ62 tank with the fuel pump (gasser - I'm told it can be used, and this is what hers has now) that has good hard lines. I have not dropped the tank because I have not seen any bubbles being drawn in from downstream of the line into the primer pump (being the only line with a bubble), so I'm not sold as the tank output line being the problem, and I really, really don't enjoy dropping the tank.
The current solutions to try:
I will try to test with a container of diesel directly feeding the soft line into the primer to see what happens, to bypass and isolate sections of fuel line.
Question:
Can a leaky injector allow air into the fuel system that will work it's way back to downstream of the primer? Can it get past the injection pump and/or priming pump?
In the meantime, any help or suggestions are appreciated. Please chime in, and ask if there is any other info you need.
Thanks very much in advance.

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Squash

SILVER Star
Joined
Dec 8, 2006
Messages
1,607
Location
Sudbury, Ont. CA
Everything before the pump is sucking and even the tiniest crack/fitting etc will allow air in and leave bubbles.
You could try putting the fuel cap on lightly in case of excess vaccum....
The return line is used to help cool the IP and should be utilized.
Injectors are pressurized and would only leave fuel behind.
Again double check all fittings and remove/loosen the fuel cap as a test.
 
Joined
Nov 16, 2010
Messages
365
Location
Squamish, BC
Hi @Squash. Thanks for your quick reply and suggestions. I checked the fuel cap for vacuum, and it didn't exhibit any sucking when I opened it. I'm re-checking all the hose clamps (worm style, not my favorite and I'm going to source a better type) and all the hard line ends were clean and smooth so those connections should be good. There is a return line from injector #4 back to the primer, and one from the back to front of the injection pump too. There is no provision for a return line to the fuel tank though. I've heard that some systems do have a return to the tank, but neither this one or my 2H do.
 
Joined
Mar 3, 2012
Messages
1,034
Location
Adelaide, South Australia
The water separator is such a common source of air/restriction.. was it actually disassembled for cleaning? Regardless, its the first thing I bypass when chasing air in fuel on a B or H engine.
 
Joined
Nov 16, 2010
Messages
365
Location
Squamish, BC
Thanks @duncanrm & @stevebradford.
I cleaned the fuel/water separator thoroughly since it was full of sludge. The top seat was clean and not corroded, and I could try a pressure test on it.
That hose is different on our 3B; our soft tube goes down about 15cm to a hard line and back to the primer. Is this the same as you've indicated? This hose hasn't been changed out.
- Oops! Steve, disregard, as I see on zooming in that your arrow points to the pipe end off the 4th injector!
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stevebradford

In the shop
Joined
Nov 7, 2016
Messages
2,106
Location
Langford. Victoria bc
Exactly, that’s the hose to check. It gets hair line cracks that can suck air but not leak diesel that you can’t see until you take off and flex it. I had the same issues you describe and that hose was the culprit.
 
Joined
Jan 9, 2004
Messages
1,667
The fuel line from the tank also looks fairly rusty. The pickup in the tank is a common place to check where the tube comes out of the tank. Unfortunately, dropping the tank is the only way to see if it is wet/leaking and sometimes dropping the tank is enough to crack the line itself if you are not careful. Using an alternate fuel source at the primer pump is a good way to see if that is the issue.
 

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